Must I log aircraft checkout flights as dual received?

Long story short, maybe. The FAA doesn't define "dual time" so it depends how you define it for your own purposes, but in practice most people use it to mean "training time". There's no definition of "dual" or "dual time" in 14 CFR part 1 or 61 and part 61 never mentions it, apart from a couple of references to "dual instruction". "Dual" is also not used in form 8710.

But "training received" is clearly defined, and 61.51 says you should log time in general if you need it to satisfy certification or currency requirements:

  (a) Training time and aeronautical experience. Each person must
  document and record the following time in a manner acceptable to the
  Administrator:

  (1) Training and aeronautical experience used to meet the requirements
  for a certificate, rating, or flight review of this part.

  (2) The aeronautical experience required for meeting the recent flight
  experience requirements of this part.

So in your example, do you need to log the time for a) certification/currency purposes, and/or b) as training received? And if you do log it, is it "dual"?

For certification/currency, it's usually best to log everything: even if you don't need to show the FAA something, your insurance company or FBO might ask you for details of your flying time.

As for training, in order for a flight to be "training received", the instructor has to endorse your logbook:

  (2) The training time must be logged in a logbook and must:   (i) Be
  endorsed in a legible manner by the authorized instructor; and   (ii)
  Include a description of the training given, the length of the
  training lesson, and the authorized instructor's signature,
  certificate number, and certificate expiration date.

That's a simpler case: if the instructor didn't sign your logbook then you didn't receive training.

But let's say that you decide to log the flight for one or both of the reasons above. Is it "dual"? Well, since there's no official definition of "dual" then it depends what you use it to mean.

Again, practically speaking, most people use "dual" to mean "training": my logging software uses it that way, and many paper logbooks seem to as well. So I only log dual if I have a corresponding endorsement from my instructor. (The software also has options like "instructor on board" or "introductory flight" that I can use for the scenarios you described.)

As a specific example, I did an FBO checkout ride in a new aircraft type a few months ago. I was already rated for the aircraft category/class and the instructor with me didn't endorse my logbook, he just updated the FBO's internal documentation to state that I'm now allowed to rent it. So I logged the time as PIC, but not dual.


Why are emergency vehicles needed for a runway excursion?

Why are emergency service vehicles necessary?

Something might have been damaged. What if something was and there is a fuel leak somewhere? Hydraulic leaks are also dangerous, and more likely as hydraulic lines run to the brakes and nose wheel steering. Better safe than sorry, so emergency services go check.

Sometimes, they also disembark passengers via the ladder if it looks like towing the aircraft to terminal will take too long and the aircraft is on unpaved surface where the mobile stairs have trouble going.

They can also help with moving the plane, especially on smaller airports that only have one runway and so have to close until the plane is moved away anyway.

  I would think the plane is more than capable of getting back onto the Tarmac, so why doesn't it?

No, it isn't. Aircraft not designed for unpaved surface will usually sink in somewhat, especially if the ground is wet, and require a lot of power to pull out. Sometimes, the tow truck is enough to get it out, sometimes they have to put planks under the wheels and sometimes they have to get out hydraulic jacks or inflatable support bags.

Even if the plane did not dig in and is easy to move, providing the power with the engines is not a smart thing to do, because the engines will throw up dirt and stones that could damage them, other parts of the aircraft, or something else around. Tow truck is much better for that job.


Can repeated call-signs be present in one day?

It is no problem to have the same call sign on the same day. As long as the same call sign is not uses at the same time there is no problem.

For VFR flights, the same call sign can even be used at the same time as long as it is not in the same airspace.

Many of the ADS-B duplicated call signs on a single are aircraft registrations coded in the transponder's aircraft ID field, typically from General Aviation flights


Where can I find data tables for lift and drag coefficients of airliners?

My first thought was: Abbott-Doenhoff. They wrote a book with lots of measurement data, and you can find it here. Of course, this was all long ago, but public data for the airfoils of today's airliners are not published.

A lot of data is also freely available in old NACA and NASA reports, however, you need to know what data you want to search for it efficiently.

If you want to focus on glider airfoils, the Stuttgarter Profilekatalog would be my next source, but unfortunately there are still people who want to make money from it even though the work was financed with public money. This is also quite old, and more modern airfoils from Delft University are similarly restricted.

Another great source is the UIUC airfoil database, but here the focus is on section data and not on polars. But it contains many useful links with airfoil data.

And then there is always XFOIL: Feed it with the coordinates, and you get very good simulations of what a wind tunnel would measure, at least as long as most of the flow is still attached. Lots of plotting functions will help to uncover what is going on in much more detail than any wind tunnel data could ever hope to do.


Which airport is featured in this Delta commercial?

It's Paine Field (KPAE) in Seattle. It has both 16L and 16R and has water (the Puget Sound) directly ahead if you're taking off from the 34s. 34L is also the only runway there large enough for most jet traffic, so that's what a Delta jet would be using if it were there.

It's also worth noting that this commercial is about flight testing and Paine Field just so happens to be the home of an aircraft production facility for some little company named 'Boeing.' You can see their Everett Production Facility on the North side of the airport in the Google Earth view and the aerial photo below. Interesting fact: that facility, originally built in 1967 to produce the Boeing 747, remains the largest building in the world by volume even to today. It's 79% larger than the next largest building and a full 3.63 times the size of NASA's Vehicle Assembly Building, the previous largest building in the world by volume, where NASA performed final integration of the Saturn V and Space Shuttle stacks and where it will do so for the SLS.

Here's the Google Earth view, and it looks like the two islands on the left in the commercial are Hat Island and Camano Island:

Sectional Chart Showing KPAE

Aerial View of Paine Field - Source: Wikipedia

Honestly, the claim of there only being 1 airport with any given runway number seems rather suspicious, since there are only 18 possibilities. Granted, the requirement of having parallel runways makes it a little less unlikely, but still many (if not most) large airports have parallel runways.


Why aren't 737s or A320s commonly used for transatlantic flights?

There are many factors that would increase the business cost for taking an operation across the Atlantic/borders:

ETOPS
Crew accommodation overseas
Acquiring airport slots in Europe
Aircraft cycles (two flights for one destination)
Cruise speed (being 10-12% slower is huge over long distances)
Geography, especially latitude.

I will focus on the sixth point, latitude. The comparison of types/distances and geography is a key point.

Looking at FlightAware for JFK to LAX from Sat 07:00AM EDT to Sun 10:43PM EDT, and copying the timetable into a spreadsheet, this is the types breakdown:

Clearly lots of narrow-bodies on that route. Let's do a distances check:

(gcmap.com)

So our best bet is the Gander option, which is 2,043 NM as the crow flies and is comparable to JFK-LAX. Doable, right? Here comes the latitude:

(wikimedia.org)

For most of the time, the polar vortex is strong and doesn't affect the contiguous US that much (watch jet stream forecast animation here). When it weakens, this is when the US weather makes international headlines, and the jet stream drops in latitude. So, for most of the year US transcontinental flights don't face fast headwinds, the story is different for the North Atlantic – compare below:

  When the polar vortex is weak, high pressure zones of the mid latitudes may push poleward, moving the polar vortex, jet stream, and polar front equatorward.

Back to the 2,043 NM distance. We'll add 10% to that for diversion and whatnot – a lenient ballpark figure. Now add 100 knots headwind, and the air distance has become 2,890 NM (at cruise speed of 447 KTAS for the A320).

From the A320 airport planning manual, the 2,000 NM permits almost the full payload of 20 tonnes (181 of 186 seats occupied). 3,000 NM on the other hand drops the utilization to 58%.

Our daring airline will now fly half-empty A320s, has to double the fare because of that, put the passengers through a technical stop, and take at least 80 minutes longer – because of the polar vortex. Add the other 5 factors, and it's a no-go for low-cost carriers.

One of the A321LR's (aka A321neoLR) key solutions is the additional fuel tanks and more efficient engines, giving an initial range of 4,000 NM. This range solves the payload problem, and this kind of specialization is a big deal at the moment, which may render this answer historic in the coming years.


What exactly happens when power is reduced in trimmed, straight and level flight?

This makes sense and is approximately what happens if you reduce thrust during trimmed straight and level flight. The aircraft will go though a series of damped oscillations, called 'phugoid' until it finds its new equilibrium state. The new state will be the original airspeed, but now in a constant descent.


why some airplanes have their exhaust gases vectored above the wing?

Assuming that both props are rotating clockwise as seen from the rear, the orientation of the exhaust pipes makes sense if the goal is to ensure that the exhaust gasses are kept clear of the wing.
The rotating propwash will tend to carry the exhaust from the right-side pipe (in rear view) of each engine well below the wing.  If the left-side exhaust pipes were similarly positioned, their exhaust would be carried up by the propwash to impinge directly on the wing.  The position we see in the photo helps ensure that the propwash carries the exhaust from the left-side exhaust pipe of each engine well above the wing.
A comment from another ASE member (John K) has stated that exhaust impinging directly on the wing can lead to galvanic corrosion due to carbon deposits.


What US airports have approaches with LAAS?

The Local Area Augmentation System was the FAA term for the Ground Based Augmentation System (GBAS), which is an International Civil Aviation Organization (ICAO) standardized system for local area differential systems.

The FAA has migrated to the ICAO term GBAS, though Several historical FAA documents still retain the LAAS terminology.

According to the FAA GBAS FAQ page,

  Currently, two U.S. locations have obtained operational approval for public GBAS use and support revenue airline traffic. These stations are located at Newark Liberty International Airport (EWR) and Houston George Bush Intercontinental Airport (IAH).

According to FAA, development of GBAS continues and,

  The FAA and other States are in the process of validating proposed ICAO GBAS standards to support Category III (CAT-III) precision approach operations. The FAA expects ICAO will approve GAST-D Standards and Recommended Practices in 2015

Also,

  The FAA continues to validate the GBAS CAT-III requirements as part of the Next Generation Air Transportation System (commonly known as NextGen). The FAA has currently deferred any Federal acquisition decision on GBAS.

Also, though GBAS and WAAS are mutually exclusive at present, some future aircraft like A350 are expected to support both GBAS and WAAS.


How was this airline (statistically) never had a fatal incident?

First of all, Ryanair has more than 700,000 flights per year now, but not during their entire 35 year existence. The total number of flights you give is therefore too high.

Assuming aircraft accidents are purely statistical (which is not true, of course), one can estimate the number of accidents you expect using a Poisson distribution: the probability of having $ k $ incidents with $ \lambda $ expected incidents is given by

$$ P(k) = e^{-\lambda} \frac{\lambda^k}{k!} $$

To get the expected number of incidents, we take the overall accident rate of 1 in 2.5 million flights (aviation-safety.net, for 2018, has been higher during the last 35 years) and multiply it with the total number of flights. For 25 million flights this would be $ \lambda = 10 $. This results in in a probability for 0 accidents of only $ P(0) \approx 0.004 \% $. Even when assuming 12.5 million flights in total (as suggested by David Richerby in the comments assuming a linear increase from 0 to 700,000 flights per year), one still obtains $ P(0) \approx 0.67 \% $ with $ \lambda = 5 $.

This means Ryanair is indeed safer than the average airline flight world wide, but so are many other EU or US airlines. Safety is not just a statistical coincidence, regulations are very strict in Europe and training is good resulting in higher than average safety records.


Is RTCA DO-260 Change 1 the same as DO-260A?

DO-260 change 1 is not DO-260A.

DO-260A released in April 2003
DO-260A change 1 in June 2006
DO-260A change 2 in December 2006

The releases marked as 'change' contain editorial changes, clarifications and corrections, but are effectively the same specification.
The alphabetical versioning is for subsequent releases of a new specification of the same system. In these releases the specification is changed, i.e. the behaviour of the system specified is different.


Why do tailplanes provide down force, if not for longitudinal static stability?

Because the safe situation is: a gravitational moment nose down, trimmed with an aerodynamic moment nose up. In all flight conditions. The critical situation is not cruise, but the conditions at low speed.

At TO and landing the Angle of Attack is high: a nose up attitude, commanded by a downward tail force. Velocity is low, so the large force is achieved by a large upward deflection of the elevator and/or a negative stabiliser incidence. The AoA range is from around zero in cruise, to 15-20 deg nose up: the required elevator range is from zero deflection to large up deflection (plus superimposed manoeuvre requirements down & up). The average required force is downwards.
You don't ever want the horizontal control surface to stall, but particularly not at low airspeeds = during take-off and landing, the most critical phases of the flight. Placing the tail at a lower average incidence angle than the main wing means that there is Angle of Attack margin: when the main wing approaches stall AoA, the tail surface has some AoA left before stalling. This implies that in cruise, if the wing has zero pitch angle, the horizontal tail has negative pitch angle.

But despite the lower incidence, the horizontal tail could stall or partly stall, for instance in a sideslip where a large portion of the horizontal tail is in the wake of the aft fuselage. If it does, we want the aircraft to have a nose down moment, not a nose up moment. If the wing is not stalled yet, the lift force is now not in n.p.$_{fixed}$ anymore, but in a.c.$_W$ And that implies that in the above situation, the nose moves up and the main wing will stall as well. Only when the c.g. is in front of the a.c.$_W$ and the tail force is downwards, will there always be a nose down moment in a stalled tail situation.
And in line with 2. and 3.: it must be certain that there is a stabilising moment in all flight circumstances, at all airspeeds, all angles of attack, all angles of sideslip. That is hard to guarantee when the main wing is optimised for cleanest aerodynamic flow and the stabiliser is in the wake of the main wing: efficiency of the main wing will be higher in all circumstances. By choosing an equilibrium state where the horizontal tail produces a downforce, and therefore less lift with increasing AoA, this problem is solved and the guarantee can be issued, without any additional analysis required. Very good in the olden days of aviation, before CFD.

Note that all above considerations are not really a huge concern in cruise: can the horizontal tailplane ever encounter a vertical wind gust with a velocity that can stall it? The velocity triangle says no, this is not likely to occur in 10$^9$ flying hours. A large aircraft can apply Relaxed Static Stability in cruise: pump fuel to the tail tanks and reduce average down force plus associated trim drag to a minimum, because AoA at cruise is very low. Or trim such that the stabiliser has an upforce, like in the drawing where there is static stability. But at start and landing, the trim tanks must be empty!

The additional burden for certifying this situation is a more elaborate analysis considering gusts at cruise altitude and the influence on static stability: are there any vertical gusts at a higher frequency than 10$^{-9}$ flying hour that can destroy the static stability? Such an analysis was impossible in the starting days of aviation, it is possible now of course.


When must delegated airspace be listed in the AIP?

Principles under ICAO agreements

Delegation of ATC services is contracted between ICAO members using bilateral or multilateral letters of agreement. Cases of such delegation exist typically to cover remote large airspace (e.g. Arctic agreement between multiple countries), or small areas (e.g. islands).

ICAO members are committed to fulfill the decisions of their constituent act, the Chicago Convention signed in 1944. Among the annexes to the Convention, annex 15 is related to the provision of aeronautical information services (AIS):

  Annex 15 defines how an aeronautical information service shall receive
  and/or originate, collate or assemble, edit, format, publish/store and
  distribute specified aeronautical information/data. The goal is to
  satisfy the need for uniformity and consistency in the provision of
  aeronautical information/data that is required for the operational use
  by international civil aviation.

Impact on AIP

Annex 15 includes these generic articles:

  3.1.1.2 Each Contracting State shall take all necessary measures to
  ensure that the aeronautical information/data it provides relating to
  its own territory, as well as areas in which the State is responsible
  for air traffic services outside its territory, is adequate, of
  required quality and timely. This shall include arrangements for the
  timely provision of required information/data to the aeronautical
  information service by each of the State services associated with
  aircraft operations.

and

  3.1.7 An aeronautical information service shall receive and/or
  originate, collate or assemble, edit, format, publish/store and
  distribute aeronautical information/data concerning the entire
  territory of the State as well as areas in which the State is
  responsible for air traffic services outside its territory.
  Aeronautical information shall be published as an Integrated
  Aeronautical Information Package.

I was not able to find the decision to use AIP ENR 2.2 (other regulated airspace), but it's a matter of fact the information is found here, e.g. in the Norway AIP:

  5: Delegation of Responsibility for Provision of ATS

  5.1: General Denmark, Norway, Sweden and the United Kingdom have
  arranged through the exchange of bilateral Letters of Agreement to
  transfer the responsibility for provision of ATS within parts of their
  own area of responsibility, to their neighbouring State.

  Procedures and communication within the said areas will be as if the
  airspace was an integral part of the FIR for which the nation
  mentioned is responsible.

Bidirectional scope

An effect of these articles is both the delegating and the providing states shall publish information about related areas. For example in the Spanish AIP, two cases are described.

Spain delegating to Portugal:

  By agreement between Sevilla ACC and Lisboa ACC, the air traffic
  service is provided by Lisboa ACC within the airspace defined by [...]

Spain receiving delegation from Portugal:

  By agreement between Lisboa ACC and Madrid ACC, the air traffic
  service is provided by Madrid ACC within the airspace defined by [...]


Is King Khalid International Airport in Riyadh actually very big?

It depends how you define the airport. I don't think your Google Maps method is sound, however; it depicts built-up areas, not the airport boundary. You couldn't draw the same map around LAX, say.

The standard for measuring the area of an airport appears to be the total land owned by the airport. And jet age airports, with their expansive noise buffers and office park reservations, tend to take as much as they can get. DEN is reckoned the largest airport in the U.S., at 33,531 acres (~136 km²), though only a fraction of this is developed.

The numbers for total land are easy to find, the numbers for improved land less so, but I found an informative Globe and Mail article about Montreal-Mirabel. When originally created, the land seized for the airport was larger than the city of Montreal itself— around 97,000 acres (~392.5 km²). The article notes that the airport perimeter itself was only about 5,200 acres (~21 km²). Still, it's the former number that is commonly bandied about, and the measure by which Mirabel was considered the largest airport in the world.

According to Kable, a London-based business information firm, King Khaled International Airport covered an area of 225 km² when it opened in 1983.

In 1999 it was surpassed by King Fahd International Airport, which occupies 776 km². This is roughly the figure given by the 2013 Guinness Book of World Records.


What are the ICAO equipment codes for those Garmin units?

For the GTN 6XX/7XX and GNS 4XXW/5XXW they are:

A1/B2/C2/D2/L1/O2/S1/S2

Source: garmin.com — scroll down to the link that reads: "Garmin Flight Plan Information Excel file".


How are VFR / GAAP approach points selected?

The reason for VFR approach points is to provide an orderly arrival procedure into busy or complicated airfields.

I’ll use the example of Bankstown airport, which is the primary GA airfield for Sydney. I have (very crudely) circled the two VFR approach points in green:

Two RN is the approach point when arriving from the south or west. This is identifiable from the air as a large radio tower next to the intersection of two major highways. To the north, prospect reservoir is even easier to see as a dam just south of another large highway. Easy identification from the air is a key requirement for a VFR point, so you don’t get lost.

Why funnel inbound traffic through these points though? Well firstly, much of the airspace over Sydney is Class C and reserved for the heavies in and out of YSSY to the east. You can ask to enter this airspace but chances are you’ll be denied. To the south you also have restricted military airspace over Holsworthy, and to the north-west (mostly out of this map) you have Richmond airbase, two no-go zones. As a VFR pilot you’re not allowed to use GPS as a primary means of navigating, so tracking via these visible approach points greatly helps in not avoiding these areas.

Using approach points also helps the Bankstown ATC. Firstly though I need to clarify that in 2010 all GAAP airports were converted to Class D airspace, which is more in line with international setups. The main change for pilots was that entering via VFR approach points isn’t actually mandatory anymore (unless otherwise stated in the ERSA, which is the case for Bankstown).

Anyway, Class D airspace has ATC but no radar. Therefore ATC relies on procedural separation – that is, pilots broadcast where they are now and where they are going, and ATC makes sure it will be X minutes before someone else says they are on the same path.  So, if two aircraft report passing Prospect within 30 seconds of each other, ATC would probably tell the trailing aircraft to slow down or fly an orbit.

You ask about the challenges of 'transition' but I'm not sure what you mean - these are the entry points for Bankstown, from which it is quick and easy to visually track to the circuit. For other Class D airfields, as I said before, now that they are no longer GAAP you don't have to enter via approach points unless otherwise stated. And if a procedure is stated, AFAIK it will always involve a VFR approach point.


Aircraft Identification: What single-engine, T-tail, commuter aircraft has a single prop but sounds like a jet?

Sounds like a Pilatus PC-12 to me.

image source: Wikipedia, photographer: Chris Finney


Could a flight ever be considered to be operating under Visual Flight Rules and Instrument Flight Rules at the same time?

No, you can't be both VFR and IFR at the same time. It would be like saying that a ball is both red and blue at the same time. You are either one or the other, never both.

If the pilot hasn't received an IFR clearance from flight services, then they are operating under visual flight rules, regardless of their intentions, capabilities, or flight plan. The sole exception is in class G airspace, specifically when they're flying a pre-set departure or arrival procedure from an airport. If a VFR pilot enters a cloud (and there's no emergency in progress), then they are breaking the law, and they can't just decide later that "oh, I was actually IFR at that time".

ATC is never going to inquire about which rule set you're operating under unless there's some kind of administrative foul-up. They're the ones that either did or did not issue you the clearance, so they already know which rule set you're operating under.


What does it take from the airlines to be ETOPS certified?

The requirements for ETOPS certification by the FAA are outlined in the following Advisory Circular:

  ETOPS QUALIFICATIONS. The unique nature of ETOPS necessitates an evaluation of
  these operations to ensure that the certificate holder's proposed programs are effective. The FAA
  will review the certificate holder's documentation and training programs to validate that they are
  appropriate for ETOPS. To receive approval to conduct ETOPS the certificate holder must
  satisfy the following conditions:

  a. Airplane. The specified airplane-engine combination listed in the certificate holder's
  application must have been certificated to the airworthiness standards of transport category
  airplanes and must be approved for ETOPS. Guidance for airplane ETOPS type design can be
  found in AC 25.1535-1 and § 121.162.

  [...]

  b. Flight Operations and Maintenance Requirements. The certificate holder must show
  compliance with the flight operations requirements discussed in paragraph 303 and the
  maintenance requirements discussed in paragraph 301.

  c. Training Requirements. The certificate holder should show that it has trained its
  personnel to achieve competency in ETOPS and must show compliance with the flight
  operations and maintenance training requirements discussed in paragraphs 302 and 304.

  d. Requirements For ETOPS Approval. Before the FAA grants ETOPS operational
  approval to an applicant for two-engine ETOPS, the certificate holder must be able to
  demonstrate the ability to achieve and maintain the level of propulsion system reliability that is
  required for the ETOPS-approved airplane-engine combination to be used (appendix P to
  part 121, section I, paragraph (a)). The certificate holder must also demonstrate that it can
  operate the particular airframe and other airplane systems at levels of reliability appropriate for
  the intended operation. This can be achieved directly by a successful in-service operational
  history or by successfully validating all the required ETOPS processes according to the
  Accelerated ETOPS Application Method in Appendix 3 of this AC.

  e. Accelerated ETOPS Application. An applicant for an initial operating certificate who
  is applying for ETOPS authority at entry into service under the Accelerated ETOPS Application
  method must comply with the same requirements for certificate holders outlined in this AC. It
  should be understood that validation of an applicant with no previous operational experience
  should be more robust than would be necessary for a certificate holder with operational experience. As is the case for all Accelerated ETOPS approvals, the Director, Flight Standards
  Service must be satisfied that the applicant can operate to the standards expected of an
  experienced ETOPS operator from the first day of service.

(FAA AC-120-42B)

The referenced paragraphs 301 to 304 can be found in the same document and provide detailed requirements for operations, maintenance and training.

The details may vary around the world, but other aviation authorities will have similar requirements for certification.


Why turn mobile phones off on take off and landing?

It is unlikely that phones and other personal electronics could interfere in a way that would significantly impact communications, navigation or other systems. But, the possibility is still there, and that possibility forces the FAA to impose regulation. In most cases, device-use regulations are passed down to the airlines, and it is the airline that sets rules for device use on their flight. It's quite possible they limit device use during critical flight phases like takeoff and landing to help ensure people pay attention to safety briefings.


This one is easy. Go read the primary cause of the horrific crash of two 747's at Tenerife in 1977, and why the F/O of the KLM aircraft did not override the actions of the alleged highly-experienced captain, Jacob Louis Veldhuyzen van Zanten. Everything can be tied to a systemic culture that severely discouraged such actions, even in the face of an imminent disaster. This accident led to many changes in virtually all western commercial airlines to address this specific issue.


characteristics copied from Airbus

More precisely, copied from the package developed for Airbus by Thales.

  Thales pioneered the development and certification of FBW technology on modern aircraft, starting with the Airbus wide-body A310 in 1983 followed by the A320 family (...)

To that regard, from an official brochure (PDF), the SSJ100's avionics are also provided by Thales. As for the flight control system, it's been developed by Liebherr (cockpit controls, computers, and mechanical components). (Cropped page below showing who has done what.)

Liebherr (headquartered in Bulle, Switzerland) has an official video about it on YouTube. Where the narrator says:

  (...) Liebherr supplies the entire flight control systems from the various controls in the cockpit, to the rudder of the plane. More clearly, the aerospace equipment manufacturer designed joysticks, or here more properly called side stick controllers, in-flight computers, brake levers, pedals, and slats and flaps activation systems for the Russian regional jet (...)


A transition is a branch of a Standard Terminal Arrival Route (STAR) or a Standard Instrument Departure (SID). ACO is the identifier for the Akron VOR/DME, which is a a navaid. It’s not surprising then that you would hear of an ACO transition for both KCAK and KCLE.
I would provide a chart showing where these are, but I can’t find any plates for the older VOR navigation. All the ones I find are RNAV which use GPS rather than navaids. Although the ACO VOR/DME is still operational, they are slowly being decommissioned. The FAA may have eliminated the VOR SIDS and STARs and are now only using the RNAV routes. It’s likely that the sim is using outdated plates.
If you are unfamiliar with SIDs and STARs you can check out This question.


Has any accident been caused by poor time management, despite a perfectly done checklist?

Time management generally means selecting the most important things to do given limited time. And in context of aviation that means following the common maxim “aviate, navigate, communicate”. Which is occasionally called a checklist, but usually not.

Aviate means keeping the plane under control and inside the flight envelope, navigate means knowing where you are and where you are flying, and communicate if there is someone who should know, meaning mainly the air traffic control. And most checklists, except some memory items, only come after these three.

So an accident due to poor time management means the crew got preoccupied with something and basically forgot to monitor the flight path—there is plenty of those—and despite correctly executed checklists means the distraction involved a checklist, probably a non-normal one (dealing with some failure)—I am not sure how close the accidents I can remember of the top of my head come.

Eastern Air Lines flight 401 on 29th December 1972 is probably the best known accident that comes to mind. The crew executed their before landing checklist, but that revealed one issue. And the crew became so preoccupied in troubleshooting it that they failed to notice they inadvertently turned off the altitude hold.
In some sense the Dana Air flight 992 on 3rd June 2012. The crew correctly configured the aircraft for best glide in response to a dual engine failure, but then the pilots kept trying to restart the engines and neglected to prepare for the possibility of forced landing. The checklist for engine failure does mention this though, so ultimately they didn't execute it correctly.
The Distraction in cockpit category on the Aviation Safety Network seems most relevant, but not sure which of the accidents qualify. Maybe this Avianca 727 on 17th March 1988 or this Sky Executive L410 on 21st May 2002?

There is probably more, but it is relatively hard to search.


Why does obstacle clearance area splay outward instead of being a rectangle?

Because the navigational beacons and the indicator instruments in the cockpit are such that the system is less precise at longer distances. Second the plane must find the initial fix or intersection while flying blind under IMC before becoming aligned and so the area acts like a funnel. In some areas the terrain may limit the radio beacon signal so a wedge is all that is available.

A rectangle isn't needed because planes can't make use of the inner corners and it would be both a wasted area and a hazard as a plane may be able to get in but not out. Directly over a VOR the signal is not useable and the turns in a route must be wide enough for a large-radius turn not a sharp angle precisely over the beacon. The political types like to minimize the zone of low flying aircraft noise and building restrictions on the ground dwelling tax paying voters.
STARS are higher altitude and so the design is more forgiving and can be of simple rectangles.


The reason is a temperature difference between the lift gas and the surrounding air, and probably water uptake by the hull when descending through clouds.

A given mass of hydrogen will create a constant lift force, regardless of pressure or altitude, when at equal pressure and temperature with the surrounding air. Therefore, a change in altitude will not change the lift a rigid airship creates. Ideally.

However, air gets colder the higher you climb. The sun heats the atmosphere from below, by way of heating the ground, and space cools it from the top. Therefore, on many days the temperature gradient is bigger than its adiabatic value - that is the way thermals work! L-55 stayed at altitudes where air is -32°C according to the Standard Atmosphere. When descending, the surrounding air got warmer and also warmed up the lift gas, but only slowly. This means that, depending on the rate of descent, the lift gas lagged behind in temperature relative to the air, and this temperature difference reduced its lift capacity.

Note that adiabatic heating will already heat a gas when being compressed. The lapse rate of the atmosphere must be above the dry adiabatic value for this mechanism to work, which it is on many days. Especially behind a cold front. Note that L-55 encountered strong winds - just what you find in and behind a cold front. So it is safe to conclude that L-55 flew in labile air, and when it descended, that motion became unstable, at least close to the ground.

Kapitän Flemming simply descended too quickly. Slowing things down would have warmed the lift gas more, and less lift would have been lost. But delaying the descent has dangers of its own: The gas bags back then were made from goldbeater skin and had a certain amount of seepage. To compensate, Zeppelins started their trips with several tons of ballast water onboard, which was progressively dropped during the many hours of a normal trip. Taking a detour over France delayed the trip, so he was running short on time.

Normally, a loss of lift can be compensated by dynamic lift. With some angle of attack, an airship can create up to 20% of its weight in dynamic lift - as long as all engines are running. L-55 was blown south during the night after attacking Hull and Birmingham, and found itself far more south than assumed when dawn allowed the crew to get a ground fix. When back over Germany, L-55 ran out of fuel and dynamic lift was no longer available to compensate for the lower lift gas temperature. It made a rough landing in the Thuringian countryside near Tiefenort and had to be written off.

Literature: Heinz Urban, Zeppeline der kaiserlichen Marine 1914 bis 1918


How is V_S0 calculated for anything less than maximum weight?

All aerodynamic forces are proportional to the dynamic pressure, which is the product of air density $\rho$ and half of the square of flight speed $\frac{1}{2}v^2$. If your flight mass is reduced, reduce the dynamic pressure proportionally to keep all other parameters the same. To express this in terms of speed, you need to multiply the posted speed in the handbook with the square root of the mass ratio, like that: $$v_{reduced\,mass} = v_{full\,mass}\cdot\sqrt{\frac{reduced\,mass}{original\,mass}}$$


$V_{mcg}$ is the minimum speed on the ground at which control is possible using rudder alone upon failure of critical engine. From FAR Part § 25.149:

  VMCG is the minimum control speed on the ground, and is the calibrated airspeed during the takeoff run at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane using the rudder control alone (without the use of nosewheel steering), as limited by 150 pounds of force, and using the lateral control to the extent of keeping the wings level to enable the takeoff to be safely continued.

As the center of gravity moves forward, the rudder arm increases, improving rudder effectiveness. As a result a forward cg results in a lower $V_{mcg}$. This is the reason the tests for $V_{mcg}$  is carried out at the rear most possible center of gravity. From Advisory Circular 23-8C: Flight Test Guide for Certification of Part 23 Airplanes:

  For rudder limited airplanes with constant aft c.g. limits, the critical loading for VMC testing is most aft c.g. and minimum weight.  Aft c.g. provides the shortest moment arm relative to the rudder thus the least restoring moments with regard to maintaining directional control.

as,

  There are variable factors affecting the minimum control speed.  Because of this, VMC should represent the highest minimum airspeed normally expected in service.


If a twin-engine airplane's propellers both rotate in the same direction, do they still produce a left-turning tendency?

Yes, for the most part.

Definitely P-factor will still exist and provide a yaw torque in the expected direction.  This is why twin-engined aircraft have a "critical engine".
Engine torque will still produce a roll torque in the expected direction.
Gyroscopic precession will still produce a yaw torque in the expected direction when the aircraft pitches.
The yaw torque from the spiralling slipsteam interacting with the vertical fin-- which is normally quite significant in conventional single-engine aircraft-- is the one effect that may be be greatly reduced in a twin-engine airplane of the usual configuration, since the fin is not located in a strong part of the circulation behind either prop.


How reliable is keeping flight maps on an iPad in the cockpit?

Electronic flight bags are plenty reliable.   I carry a primary and spare iPad mini on long-distance flights, in addition to my iPhone, all of which are loaded with ForeFlight.  I also carry a USB cable and car cigarette lighter adapter with me so I can power the tablets while in flight. I reason that the risk of a failure of both iPads combined was a failure of my iPhone is so low that it’s not even worth worrying about.

Keep in mind paper charts carry their own risks with them.  They’re bulky and take up a lot of space.  You can forget to pack the right ones, flashlights can run out of power making them useless in the cockpit at night, etc.

Airlines are going to have their own SOP’s for what shorts and other navigation aids are available to their flight crews, but by and large most airlines are going over to EFBs, in fact beginning to issue them to their pilots, primarily due to the reduction in weight and other costs associated with traditional printed charts and other resources.


Can an appropriately-fitted UAS (of any size category) be flown in Class B airspace?

In general, no, you can't.

Public (Governmental) Use

The FAA maintains a page on Public Operations of UASs. There are a couple of ways governmental organizations (excluding the armed forces) can fly a UAS:

It can fly in accordance with the limitations set out in Public Law 112-95 Title I, Subtitle B, Section 334 (c)(2)(C), which are that the FAA will:

  (C) allow a government public safety agency to operate unmanned aircraft weighing 4.4 pounds or less, if operated—

    (i) within the line of sight of the operator;
    (ii) less than 400 feet above the ground;
    (iii) during daylight conditions;
    (iv) within Class G airspace; and
    (v) outside of 5 statute miles from any airport,
    heliport, seaplane base, spaceport, or other location
    with aviation activities.

So, obviously, that's a no-go for Bravo.

It can apply for a Certificate of Waiver or Authorization from the FAA, which "permits public agencies and organizations to operate a particular aircraft, for a particular purpose, in a particular area." According to the FAA,

  The FAA works with these organizations to develop conditions and limitations for UAS operations to ensure they do not jeopardize the safety of other aviation operations. The objective is to issue a COA with parameters that ensure a level of safety equivalent to manned aircraft. Usually, this entails making sure that the UAS does not operate in a populated area and that the aircraft is observed, either by someone in a manned aircraft or someone on the ground to ensure separation from other aircraft in accordance with right-of-way rules. Common public uses today include law enforcement, firefighting, border patrol, disaster relief, search and rescue, military training, and other government operational missions.

So, unless you have a really convincing argument, it sounds like the FAA is very unlikely to include in your COA authorization for your UAS to enter Class B (or get anywhere near it, for that matter.)

Civil, Non-Hobbyist Operation

The FAA also maintains a page on Civil Operations of UASs. That page summarizes how civil UAS operations can be approved as follows:

  There are presently two methods of gaining FAA authorization to fly civil (non-governmental) UAS:

  Section 333 Exemption – a grant of exemption in accordance with Section 333 AND a civil Certificate of Waiver or Authorization (COA); this process may be used to perform commercial operations in low-risk, controlled environments. Instructions for filing a petition for exemption are available here.

Surely, operating in Class B isn't "low risk" (though I suppose you could argue it's "controlled,") so this certainly seems like a no-go.

  Special Airworthiness Certificate (SAC) – applicants must be able to describe how their system is designed, constructed, and manufactured, including engineering processes, software development and control, configuration management, and quality assurance procedures used, along with how and where they intend to fly.

    a. SAC in the experimental category – may be used for civil aircraft to perform research and development, crew training, and market surveys; however, carrying persons or property for compensation or hire is prohibited. FAA Order 8130.34 is used by FAA inspectors to issue experimental airworthiness certificates and special flight permits to UAS. For more information, please contact the Airworthiness Certification Service, AIR-113, at 202-267-1575.

    If the FAA determines the project does not present an unreasonable safety risk, the local FAA Manufacturing Inspection District Office will issue a Special Airworthiness Certificate in the Experimental Category with operating limitations applicable to the particular UAS.

    b. A UAS type and airworthiness certificate in the Restricted Category (14 CFR § 21.25(a)(2) and § 21.185) for a special purpose or a type certificate for production of the UAS under 14 CFR § 21.25(a)(1) or § 21.17. For more information, please contact the Los Angeles Aircraft Certification Office at 562-627-5200.

(Bold emphasis is mine, italics emphasis is from the FAA.)

For UASs with a Special Airworthiness Certificate, FAA Order 8130.34C specifies in Chapter 3, Section 1.3 (Flight Test and Operating Area) that:

  All proposed flight test and operating areas outside of restricted airspace must be approved by the FAA. Flight test and operating areas will be coordinated with the air traffic component of AFS-80.

and that:

  The flight test area and operating area must be over open water, or sparsely populated areas, having light air traffic. The FAA is required to evaluate each application to determine that the proposed flight area does not exceed that which is reasonably required to accomplish the program.

Certainly, Class B doesn't qualify as "sparsely populated areas, having light air traffic," so this, too, seems to be a no-go.


Why does manifold pressure increase when you turn on carb heat?

Because manifold pressure sucks! Seriously though, the manifold pressure measures how much the engine is able to reduce the pressure between throttle and inlet valve by sucking air into the cylinder.

When you apply carb heat the air gets routed over a heat exchanger that uses some of the excess heat from the exhaust system to heat up the intake air, however the reason it becomes less dense, is because the pressure stays the same. If you look at the so called ideal gas law, you'll notice that pressure is a function of density and temperature, if you have a closed system, where the density can not change, increasing the temperature would indeed increase pressure. This is not a closed system however, so the pressure actually stays more or less the same and the density decreases, and it's not the reason for the manifold pressure increase.

The thinner air leaves the engine with less oxygen to burn and thus it produces less power, the RPM drops, causing the engine to "suck" less air into the cylinder, this gives the air more time to sneak passed the throttle, and the manifold pressure rises. For the same reason the manifold pressure rises (slightly) when you reduce the RPM for cruise. Any reduction in RPM, for whatever reason – engine damage for example – as long as the throttle doesn't move (or if you have carb ice, which has essentially the same effect as closing the throttle), your manifold pressure will actually rise. Remember, it seems counter-intuitive, but the engine is fighting a battle with the throttle, trying to keep the manifold pressure down by sucking the air out, while the throttle is trying to increase the pressure back to atmospheric by letting air in.

When the throttle is anything but wide open, the situation looks like this (image borrowed from the linked article)

(source: avweb.com)

It's related to the fact that the manifold pressure gauge, when the engine is stopped, will read ambient pressure, i.e. 29.92 inHg on a standard day at sea level, which is usually interpreted as "full throttle", it doesn't matter how the throttle is positioned. So it's not really showing how much fuel/air mix you're shoving into the engine. In fact, we're not shoving at all, the engine literally sucks it into the cylinder as the piston moves out of the way during the intake stroke. In this particular case with the engine off, it just means that enough air was able to sneak by the throttle and equalize the pressure. It is not flowing nearly fast enough to equalize the pressure as soon as the engine is running though.


What certifications must one have to repair/alter propellers and instruments?

I believe you need to be an FAA Certified Repair Station approved to work on instrumentation, propellors etc. as noted here

  The FAA lists and approves ratings on a form called operations
  specifications. The operating specifications will also be displayed in
  the maintenance facility, usually right next to the certificate. Like
  other businesses, most maintenance facilities advertise on the Web and
  in trade magazines, so you have many ways to research what rating a
  particular repair station may have. There are basically six ratings
  that pertain to a repair station:

  •  Airframe

  •  Powerplant

  •  Propeller

  •  Radio

  •  Instrument

  • Accessory

To be an approved Repair Station the employees must conform to

  § 145.157 Personnel authorized to approve an article for return to
  service.

  (a) A certificated repair station located inside the United States
  must ensure each person authorized to approve an article for return to
  service under the repair station certificate and operations
  specifications is certificated under part 65. (b) A certificated
  repair station located outside the United States must ensure each
  person authorized to approve an article for return to service under
  the repair station certificate and operations specifications is—

  (1) Trained in or has 18 months practical experience with the methods,
  techniques, practices, aids, equipment, and tools used to perform the
  maintenance, preventive maintenance, or alterations; and

  (2) Thoroughly familiar with the applicable regulations in this
  chapter and proficient in the use of the various inspection methods,
  techniques, practices, aids, equipment, and tools appropriate for the
  work being performed and approved for return to service. (c) A
  certificated repair station must ensure each person authorized to
  approve an article for return to service understands, reads, and
  writes English.

They also must meet the requirements set fourth in:

  (b) Meets the eligibility requirements of §65.101.

which you can find here.

You can find the full regulations pertinent to becoming a repair station here


Why does a Thrust Vector Control System increase maneuverability?

The point of thrust vector control is post-stall maneuvering.
Control surfaces lose much of their effectiveness when the flow over them is separated. Pointing the jet exhaust in different directions works almost regardless of angle of attack. All that is required is good intake flow, and by placing the intake below the forebody (as done on the X-31, the F-16 or the EF-2000), this is still possible even at high angles of attack.
Post-stall maneuvering enables the airplane to point its sensors and weapons in the direction of an opponent within seconds of detection. Compare that to flying a turn at Mach 0.8 over maybe 150°. At 6g (= 80° bank angle), this takes 11.5 seconds, assuming a speed of 256 m/s (which is Mach 0.8 at medium altitude) and an instantly achieved maximum turn rate.
By attaining a very high angle of attack in order to slow down the airplane and thrust vector controlled rotation of the fuselage into the direction of the opponent (Herbst maneuver), an airplane can turn much quicker and, consequently, shoot earlier. This is critical for winning in air-to-air combat.


Would it be practical that nuclear-powered seaplane (only flying low over the sea) or hovercraft can be an alternative to cargo plane or ship?

There is a long list of other issues as well, but in order to avoid a too long post I stuck to adressing the points you made in the question.
As with most other things this boils down to the economics. If we assume that the technical challenges can be resolved and you're able to build something that fly according to your description, it will still cost a lot to develop and build. But how much does it cost to carry a full load from A to B compared to the other options, and how long does it take?

It may be a competitor to cargo planes or ships.

Ships are great for freight because they carry a lot of stuff at once cheap but slow. Aircraft are great because they go fast and high, and are less impacted by weather, but at a higher cost while carrying less.

The flying height of this aircraft is only one or two hundred meters.

One of the advantages of existing aircraft is that when something go wrong, you can trade altitude for time to troubleshoot. Flying at a few hundred meters means less time to troubleshoot; being powered by a nuclear reactor means that you will need a lot of redundancies to minimize catastrophic system failures. You'll also be more exposed to weather, which will increase the stress on the airframe compared to other aircraft.

Flying only over the sea and can landing on the sea.

This will expose you to more salt water, which will drive both R&D costs to make the aircraft more resistant to corrosion, but it will also increase maintenance costs in the long run.
Landing and taking off from water is harder in bad weather or at night. A land-based plane can usually count on having runway lights available, and a firm surface to land on. A seaplane has neither but will be affected by waves in addition to wind.
This will also limit the routes you can fly, and therefore also the potential customers for this plane.

And the speed is low. It can be safe enough.

Flying slow will make you less able to avoid bad weather; flying around it might not be possible before it overtakes you. While in theory you could be able to land instantly in case of problems if the cruise speed is close enough to the landing speed, you'll still have weather to contend with.
Crashing at 200kph isn't automatically safer than at 800kph. Using nuclear power will limit which countries would allow operations, as one crash would be enough to destroy an entire area.

Container-sized Small Modular Reactor can be under 100 tons.

This is less than the fuel weight of a 747-8F even if you add engines. According to this question electrical engines are likely to weight around twice as much as comparable turbine engines, so with a bit of goodwill and a lot of assumptions we can replace the engines and fuel load of a 747-8F with a reactor and 8 engines.
Even if this were to work, I suspect the maintenance costs would be huge, and you wouldn't really solve a problem. Chances are you'd go slower than existing aircraft but at a higher price and with a less reliable timetable.


How to calculate the induced drag coefficient?

There's no way to calculate $e$ without using computational fluid dynamics (CFD) since it involves the calculation of complex three-dimensional flow interactions with the wing geometry (lift loss due to wingtip vortices).

For most aircraft, 0.8 is a pretty good estimate, so this is probably the value you're expected to use. If you need a more accurate number for your particular problem, you'll either have to know the specific aircraft model (in which case you would likely have to calculate $e$ given $AR$ and ${C_D}_0$, $C_D$, and $C_L$ for a certain state) or be given a number to use for the problem.


Why the inward engines-placement on the An-124?

In general, designers would like the engines to be closer to the fuselage, more like the An-124. With the low wing on the 747, the engines have to be placed far enough out that they can still have enough clearance from the ground. This trades with the height of the landing gear and dihedral of the wing at the fuselage. With a high wing on the An-124 they have plenty of room and can place them closer.

Although the engines do provide some relief to the regular bending loads from lift on the wings, there are lots of reasons to keep the engines closer to the fuselage. Better handling with engines failed is one. But it also affects the amount of wiring and tubing you need to get to the engines, and there are other loads like hard landings that are easier to design for with the engines closer to the fuselage.


The A320-318/319 or the improved A320neo-319 share the market area around 107 - 160 passengers with the CSeries (now A220), two main differences are:

The CSeries is designed generally for carrying less passengers than the basic A320-family. The fuselage of the A320-family is stretchted or compressed, exemption is the A320-318, which has also smaller wings, but at some point strechting/compressing the fuselage becomes inefficient.
The CSeries is an entirley new plane, while the A320neo seems to be more some kind of improvment with new engines and some(?) modifications to the airframe.

Basically, the airframe, fuselage and engines should fit together, to make an efficient plane. The CSeries should be therefore more efficient with small numbers of passengers. The A320-318 will be not available as neo and the A320neo-319 seems to be market for special long-distance and hot-and-high (engines produce more thrust and consume more fuel) situations.


What was the normal flight path for a passenger aircraft from New York to Miami in 1955?

Probably not a whole lot different than today. You likely won't get a very exact answer to a general question like that unless you can narrow down specifically what kind of detail you seek.

Obviously GPS waypoints wouldn't have been used, but any NDBs in use at the time probably would be. My advice would be to search for a vintage chart from that era and plot the most direct route using depicted navaids.


Why do flaperons 'move down then up' on takeoff roll on a 787?

I found this 16-year old thread on airliners.net. The Boeing 777 has the same system, and at the time it was unique in that. (You can watch it here.)

When takeoff power is applied, hydraulic power is removed from the flaperons, as not to stress the actuators for an extended duration, which causes them to drop due to gravity. They are then slowly lifted by the rushing air. At around 100 knots, power is restored to them.

The stress being avoided is from the engine's jet blast. During ground runs for an engine, the flaperon is known to flutter.

The poster cites the B777 Maintenance Training Manual Rev 4 02/08/1997. The reasoning comes from this other 12-year old thread.


With current technology the L/D might go up to 70 or 75, and going higher would require an almost impractically large wing span. Gliders need to fly in tight circles to use updrafts, and the larger the wingspan becomes, the bigger the speed difference between inner and outer wing will be. Also, landing such a wide wing without dropping a wingtip will be very hard. Smaller wings with a high aspect ratio will have a low chord length, leading to smaller Reynolds numbers, which translates into a steep increase of friction drag if the aspect ratio is increased without increasing wing area. Therefore, only adding wing span will help, and this runs into a soft wall beyond the 30 m of designs like the Eta. In addition, the current mass limit of 850 kg will make bigger aircraft unattractive for competition pilots.

The Concordia (pdf!) is claimed to have an L/D approaching 75, but I have learned over the years to see theoretical predictions as invariably optimistic, and realistic performance, with bugs on the wing and all, will never quite measure up to the hoped-for ideal.

Werner Pfenniger proposed to use boundary layer laminarisation by suction (pdf!) to reduce friction drag and proposed glider designs with L/D ratios in excess of 100. Turbines at the wingtips would drive the suction pumps, so these would still be unpowered aircraft. But so far nobody has dared to turn his visions into reality.

While laminarisation avoids the increase in friction drag of a turbulent boundary layer, a moving wall would eliminate viscous losses altogether. Now the friction generation is between the moving wall (this could be a taut foil running between two cylinders at the forward and aft end of the wing) and the fixed structure. With current materials there is no hope of reducing drag this way, but who knows what tricks will be possible in the future.

A glide ratio of 100 or more looks rather unlikely in the next 50 years.


What exactly happened with the Flight Computers on XL Airways Germany Flight 888T?

Tl;dr it was in direct law because air data was inconsistent and the landing gear was down.

For a full answer to why the aircraft did what it did I'll answer a few questions one at a time.

Why did the flight computers reject the good sensor and use the frozen ones?

The values of the sensors are fed to the control computers by the ADIRU (air data and inertial reference unit). There are three ADIRU's, each corresponding to three redundant systems of sensors. Part of the ADIRU is the ADR (air data reference). The ADR is responsible for determining the validity of the values coming from the air data sensors (pitot tube, static port and AoA vanes), correcting those values from local AoA to airplane AoA and feeding the values to the control computers. (local AoA at the sensor location is not necessarily the same as the overall airplane AoA due to their positioning on the plane.) Each ADR uses two resolvers for each sensor and compares these values for consistency. Along with the value it also sends to the control computers an indication as to whether the values are valid or not.

The ELAC (elevator/aileron computer), which controls movement of the flight surfaces takes the values from each ADIRU and compares them against the median value. If a sensor deviates from the median value past a certain threshold it assumes sensor failure and rejects the input. It then uses the average value of the other two.

Unfortunately for the crew of XL888t this method anticipates a single sensor failure. When two sensors fail at the same or similar value the system will reject the working sensor. There is really no way to overcome this, but having two sensors fail at the same value is exceedingly unlikely.

Why did the control laws degrade?

This is really the crux of the question. The ELAC is what determines the control laws. It uses information from the aircraft configuration (flaps, slats, air brakes, undercarriage)and the output of the ADIRU to determine how to interpret the pilot's control inputs. It uses this information to determine the α protection speeds (α-prot, α-floor and VLS) and when to engage the automatic envelope protections.

Normally when the aircraft slows the AoA increases unless a nose down input is given. In the case of XL888t the pilots were intentionally trying to put the plane into a stall in order to demonstrate the α protections. The elevator and stabilizer were in full up position and the engines were slowed. The ELAC will allow this position until it reaches the calculated values for α protection. In this case the AoA was not changing. When the parameters the ELAC is using get so far out of their thresholds the ELAC can no longer make the necessary calculations, so the α protections are disabled and control law is degraded to alternate.

So why did it go into direct law?

The test the crew was performing at the time was low  speed  check  in  landing  configuration." Landing configuration obviously indicates that the landing gear be down. In alternate law roll control is in direct law, but pitch control is still as it is in normal law, with automatic trim, etc.,except without α  protections. But when the landing gear is down the pitch control shifts to direct law and autotrim is disengaged. The "USE MAN PITCH TRIM" warning is displayed on the PFD.  It's the pilots' failure to notice this warning that resulted in the crash.

As to why the control laws are designed this way I can't say. Maybe someone else can explain why Airbus made that choice.

Note: All of this information was taken from the BAE final report.


What are early/inside and late/outside turns (see, e.g., PBN Manual Order 8260.58A) and when do pilots perform them?

I think what you're talking about are what pilots refer to as "fly-past" and "fly-over" waypoints.
Up until recently, all waypoints in the world were "fly-past", ie you could cut the corner from one leg to the next and not actually fly over the waypoint itself. This is still the standard, unless otherwise stated.
But then some SIDs and STARs needed people to actually fly OVER the waypoint before turning onto the next leg, and so coding was included in FMCs etc to get the autopilot to not start the turn until AFTER the waypoint. The difficulty is that there's usually not any differentiation in the presentation on the CDU between "fly-over" and "fly-past" - you have to look at the produced track on the ND to then see whether you're cutting the corner or turning after the waypoint.


What does "zero offset between two waypoints" mean in ICAO Doc 4444?

GNSS units have the ability to fly an offset, meaning a track parallel to the one drawn between 2 waypoints. For example a left offset of 5 NM means the track is now 5 NM to the left of the original track and running parallel to it.

The lateral separation minima specified in 5.4.1.2.1.2 for two aircraft (both GNSS) on intersecting tracks require that neither be flying such an offset – since the tracks intersect at a common waypoint that is used for separation, an offset would change this common waypoint. Here's a crude representation (blue track is an offset):


Are go-arounds prohibited at St Barth (TFFJ)?

The video's description reads:

  After passing Eden Rock (min 02:39) it is prohibited to conduct a Go Around.

Below is at 2:39:

The official eAIP reads (link may die):

  AD 2 TFFJ.AD 2.22 Flight procedures

  22.2 Arrival flights:
  RWY 28:

  Going around is prohibited in short final.

If Eden Rock is that tiny island on the left, then it makes sense as the plane would be aligned and on short final after passing it, where a right break option is no longer available.

So the answer to the first two questions is yes.

The reasons are not on the chart, so possibly the clearance gradient was not met, was not demonstrated, or the risk to the road and community past the tiny hill is too high.

Also note AD 2 TFFJ.AD 2.21:

  Take-offs on RWY 28 prohibited.

(eAIP chart)


What does "RA" mean in the FAA Terminal Constraints?

-RA is the METAR code for light rain.

LOCIGS is low ceilings, and TSTMS is thunderstorms.*

* Air Traffic Management Glossary of Terms (faa.gov).


What is the procedure to follow for "traffic not in sight"?

Please don't use "Not in sight". Parts of radio transmissions, such as single words, can easily be cut off or missed, making it sound like you said "In sight". I commonly hear pilots use the phrase "Looking out" or something similar, which conveys a clear message: "I understood what you said, but I don't see the traffic yet".

ATC provides traffic information when there is a risk of conflict, or in the traffic circuit if we want you to follow another aircraft. No matter the reason, we will continue to update you on the traffic either until it is no longer a factor, or until you report having the traffic in sight. So, when you receive traffic information, keep looking until you see the traffic. We will keep you updated as long as it is still relevant. And please do report when you spot the traffic, that is a super helpful piece of information to us.

In the traffic circuit specifically, if you can't see the traffic being called out, you can always ask the tower to confirm you are cleared for base and final turn. When I have someone on downwind who can't spot the aircraft to follow, I will typically just tell them to continue downwind and then I will call their base turn when appropriate. But, as always, if in doubt, ask.


What is that decommissioned plane near Nadirgul Airfield?

This is right, this model is a C-47A-85-DL Skytrain, a variant of the "Dak" DC-3 selected by the US Army Air Force in 1941 as its standard transport aircraft.

Image from Le Bourget Air & Space Museum

It has been early used by Allied forces to drop paratroopers and equipment or to tow gliders behind the coastline for the D-Day and operation Overlord.

C47 from 439th Troop Carrier Group and Waco with their invasion stripes taking off from England for Utah Beach, June 1944 (source)

It had a long history and was everywhere until the end of the war and in the post-war conflicts, e.g. many of them participated to the Berlin Airlift:

C47s unloading at Templehof airport in Berlin, 1948. Source

Differences with the DC-3 include:

cargo door
hoist attachment
strengthened floor
shortened tail cone for glider-towing shackles
astrodome in the cabin roof.

You said the aircraft was standing at Nadargul airstrip. This information has been very useful to find the exact aircraft. It happens the aircraft did have a long story, throughout eras of war and peace, linking people of many countries:

A C-47A-85-DL airframe with c/n 20012, is manufactured in Long Beach, California, by Douglas (source) for the USAF (registration 43-15546).
In 1946, right after the war, it becomes the French government property (F-BAXK) operated for cargo flights under Air France colors.
Sold in 1950 to Portuguese government to be operated from Lisbon by Aéro Portuguesa (CS-ADB).
1953: Leaving Europe when sold to Lebanon, operated by Air Liban (OD-ABQ).
Finally moving further eastwards to India, bought by Kasturi and Sons (VT-DTS) to deliver The Indu newspaper in distant areas until it is decommissioned and transferred to Nadargul where it is used now by the Flytech Aviation Academy for ground training (source).

(Source)

A movie star

This aircraft is seen in the 1965 Hindi feature film, Gumnaam (video):

Stamps in Israel

The aircraft was used for the first aerial mail sacks sent in 1948 from Israel to European countries, when it belonged to Air France. Two stamps commemorated in 2008 "60 Years of Friendship between Israel and France":

  On June 9, 1948 an Air France DC3 airplane, registration number
  F-BAXK, landed Haifa, flown by pilot Georges Bernard and two crew
  members: communication technician Mr. Sortais and mechanic Mr. Boutet.
  The plane made an interim stop in Bucharest while en route to Israel,
  thus arriving with mail from both France and Romania. The plane
  subsequently left Haifa on June 11 at 6:36 a.m., bearing mail to
  France and other countries with which Israel had re-established postal
  ties: Bulgaria, Holland, Hungary, Yugoslavia, Poland and Switzerland.
  It also carried a mail sack bound for New York. After interim stop in
  Cyprus, Greece Italy and Nice in southern France, the airplane took of
  the next day towards its final destination, Le Bourget airport in
  Paris, where it landed on June 12, 1948 at 11:01 a.m. and delivered its
  mail sacks.

(Source)


Could the stick position be used as a Angle of Attack indicator?

For a given set of configuration parameters, CG, weight, power, G loading, you could theoretically use stick position as an approaching stall indication.  Problem is, the actual location would vary with all those parameters, so if you had a stall indicator device that was measuring and displaying stick position, you would constantly have to vary the calibration with power setting, flap position, G load, all up weight, and center of gravity.

So, take the apparatus you would have developed to go under the floor to measure where the stick is at, and move it out to the wing with a vane that gets blown on in the clean air flow, have THAT drive your indicator, and voila!  No need to adjust for any configuration variables and you know exactly where you stand relative to stall at all times and in all flight regimes.


Why do countries not bound by US law comply with the FAA's originate airworthiness directives?

International air travel requires compatible laws at both ends, otherwise a plane might be grounded when it arrived. A web of international agreements therefore exists to implement globally the directives of the major national certificating authorities such as the American FAA and European EASA.
Some planes made in Russia and China are not able to fly internationally to any significant extent because they do not meet FAA or EASA standards. Others have been certified by these authorities and do frequent Western airports.
The agreements are voluntary. For example the Boeing 737 MAX scandal led many national authorities to reject the FAA's judgement to let it keep flying immediately after the second crash, and to make their own judgements when the FAA re-certifies it, while the EASA has been negotiating hard to ensure that the fixes are also compliant with EU standards.


What are the rules for close/formation flying of civilian planes?

Pilots are allowed to fly as close as they want to each other as long as all parties agree to it and feel safe doing so.

Air Traffic Control cannot guarantee separation for planes in formation flight,So this will only be done under VFR and in VMC, where pilots can maintain visual separation from each other.

Many stunt fliers are civilian pilots and will routinely fly in close formation as well.

Other notable example of civilian formation flight include Mythbusters testing airplane fuel efficiency in formation and Airbus' publicity stunt with 5 A350s


Why is the nose of the Mig-21 shaped so differently compared to other fighter aircraft?

The nose design of aircraft, like any other part, is a result of optimization in response to a number of factors. The Mikoyan-Gurevich MiG-21 'Fishbed' is a supersonic, second/third generation Soviet fighter/interceptor.

The first jet aircraft to enter serice during the WWII, the Messerschmitt Me 262 'Schwalbe' and Gloster Meteor had twin engines in their wings. In these cases, the nose was designed to carry the cannons, which were the primary armament at the time.

"Messerschmitt Me 262A at the National Museum of the USAF" by USAF museum - http://www.nationalmuseum.af.mil/shared/media/photodb/photos/040820-F-1234P-081.jpg. Licensed under Public Domain via Commons.

The first generation jet fighters, like the F-86 and Mig-15 were subsonic and had engines buried into the fuselage to reduce drag. The nose, again carried the cannons (in case of Mig-25, in the lower fuselage).

"F86Sabre" by Kowloonese at the English language Wikipedia is licensed under CC BY-SA 3.0

However, the second generation jet aircraft were the first operational jets to go supersonic. The Mig-21 was designed in response to a Kremlin specification, which called for Mach 2 level speed (at altitude), while carrying a simple radar and option for future air-to-air missiles.

As the jet engines require airflow to be subsonic at entry, the flow has to be decelerated before reaching the engine. Early in the design (from Ye-50-3), Mig decided to use a conical centerbody for this purpose, as it was decided that the aircraft would be single engined with engine in the fuselage (the engine was supposed to be the Mikulin AM-9B, however, the aircraft ended up using Tumansky R-11).

This nose design decelerated the flow using two oblique shocks and a normal shock, giving improved pressure recovery at high supersonic Mach numbers. The center-body (cone) moved axially according to the Mach number. Also, the center body housed the radar and associated equipment.

The first generation Mig 21s only had a range finder, and the intake diameter had a smaller cone.

"Mig21F13web" by Newresid stephanelhernault@yahoo.fr - Own work work vector drawig travail personnel dessinn vectoriel. Licensed under CC BY-SA 3.0 via Commons. (Image cropped)

The following image shows the range finder used in early models of Mig 21.

"MiG-21F-13 radar Keski-Suomen ilmailumuseo" by MKFI - Own work. Licensed under Public Domain via Wikimedia Commons.

The photo you've shown are from the later versions (Mig-21 bis from IAF), which had the radars from the "Sapphire" family. To fit the radar antenna into the cone, the cone had to be made bigger, therefore the whole front fuselage had to be redesigned, the diameter of intake got more than 200 mm higher, and the cone itself got longer, wider and moved forwards.

"Mig21fishbedHfamilyweb" by Newresid stephanelhernault@yahoo.fr - Own work work vector drawing travail personnel dessin vectoriel. Licensed under CC BY-SA 3.0 via Commons. (Image cropped)

The following figure shows the enlarged nose cone section housing the radar. Interestingly, the nose cone seems to be made out of (metal tipped) wood to prevent interference.

Source: toad-design.com

A number of aircraft from that time had conical body inlets, like the British Electric Lightning.

"Lightning.inflight.arp.750pix" by Arpingstone - Own work. Licensed under Public Domain via Commons.

The F-16, on the other hand, has a simple normal shock diffuser. By the time of F-16, the radars had become bigger and more important (AAMs have become the primary combat weapon, replacing guns), and needed more space in the nose. As a result, the inlets of most of the aircraft had moved to the sides/downwards. The following figure shows the AN/APG-68 radar in F-16.

Source: defenseindustrydaily.com


Could propeller wash provide sufficient lift to take off - even in theory?

Yes.  The wing doesn't care what is causing air to flow past it.  Headwind, propwash, 747 wake, gopher sneezes.
If the airplane is restrained from forward motion, and the propwash over most of the wing is fast enough, let's say more than the airplane's stall speed, then the wing must generate enough lift to support the airplane, causing it to take off.
It's not so much a matter of designing the wing specially, as making the airplane tolerate the many large props needed, and the weight of the engines.  That much power is too much for efficient cruise.  But it's easy to implement with a one pound model airplane.


Should head stay level or inclined in a bank?

I am not a glider pilot, but the principle holds for flying any fixed wing aircraft1: you should keep your head level with the aircraft, as you described, not the horizon.

As your instructor explained, there may come—or will come—a time when you are not able to keep your head level with the horizon due to the nature of a particular maneuver or orientation, and that is a practical matter to consider. It is certainly difficult to incline one's head 60° to the side in a steep turn.

From my perspective, however, the more important reason is that your frame of reference needs to be the aircraft. You are used to viewing the world with the ground as your frame of reference; down is down, up is up. As you learn to fly, however, you need to learn a new way to view three dimensional space, or—more specifically—the way you move through that space in the aircraft. It might sound cheesy, but you really need to learn to become one with the aircraft and hold the same perspective regardless of the aircraft's orientation.

Now, that being said, as you gain experience and develop your skills, you may come to realize that this perspective shift does not always require that your head remain rigidly perpendicular to your shoulders. Rather, it is a matter of perception which will eventually be independent of how your head is oriented relative to the aircraft. At my first flying job I spent much of my time in maneuvering flight and my head was rarely still—much less level with the aircraft. I spent a great deal of time with my head on a swivel, looking up and down, side to side, craning forward to clear into a turn, looking back into the cockpit, etc.

At this stage in your training, however, it is probably important to train to keep your head straight within the aircraft; certainly follow your instructor's instructions, and you should do well.

1This probably holds true for rotorcraft as well, or any aircraft for that matter. I am only sharing what I am familiar with.


Why is there no 100% power in the POH power setting table?

There are no 100% power setting tables because it is impossible to cruise at 100% power with a normally aspirated engine.

100% power is rarely available, even at takeoff.

It is only available at sea level when the temperature is 15C and the altimeter setting is 29.92".


Do large non-pressurized metal planes have a maximum fatigue cycle?

Yes they do, and here is why.

Airplanes are made mostly of aluminum rather than steel. It is possible to design a steel part in such a way that it will never succumb to fatigue failure (crack propagation at a stress significantly below the yield stress) but this is not true of aluminum and its alloys. For this reason it is necessary to periodically tear down and inspect aircraft for fatigue cracking of their aluminum structure- in essence, safety is inspected into (aluminum) aircraft because from a design standpoint, it is not possible to design fatigue failures out of their structure.

During that teardown, any part that shows fatigue cracking (or corrosion, or physical damage, etc.) is removed and replaced with a new part that is certifiably fault-free. To some extent this means that a DC-3 with 40,000 hours on it has had so much of its structure replaced over the years that the joke is told that the only part that actually has 40,000 hours on it is the serial number plate.

Flexure of the structure during turbulence in flight is a more significant source of fatigue cycling than cargo loading & unloading cycles.


In short, the people sitting over the nose wheel use the ICAO codes, and the people in the back use the IATA codes.

The IATA is the International Airline Transport Association. The ICAO is the  International Civil Aviation Organization. While you are correct, the IATA does not have more than 17500 codes, their primary concern isn't creating codes for every airport including grass strips and private airfields. It is easy to think of IATA codes as being concerned essentially with identifiers that the passengers will need.

As far as ICAO is concerned, they contain a country identifier in their codes. They can even be more than 4 digits, as in the case of RU-2244 (Ukrainka Air Base). The vast majority are 4 digit or 5 digit, with the first 1 or 2 as the country code.

This allows ICAO to be available for every airport in the world. It is very common to refer to the IATA codes when flying locally, let's say within the USA, and refer to the ICAO if flying internationally.

I have a database structure of all airports in the world (or at least all known ones). This includes any grass/water/helipad/paved runways.

There are a total of: 46,465 airport/airfields including those that have been closed.

Source: http://ourairports.com/data/


Has any airliner ever collided with a glider?

Yes.  (I found this by Aaron Holmes's hint that he searched only English sources.)
On 1999 Feb 12 at 3:40 pm, a Grob G103 sailplane F-CGXB (possibly "in wave flight") collided with an Airbus A 320 F-GJVG at 8600 feet, near Montpellier, France.  Both landed safely with minor damage.  There were no casualties.
Summary: https://aviation-safety.net/wikibase/24140
Accident report, excerpted below:  http://www.bea.aero/docspa/1999/f-xb990212/pdf/f-xb990212.pdf

L'Airbus A 320 à destination de l'aérodrome de Montpellier Méditerranée est
autorisé à descendre vers le niveau de vol 80. Dans le même temps, en vol local
autour de l'aérodrome de Saint Martin de Londres, le planeur G 103 évolue vers
8 600 pieds dans une ascendance au-dessus de la montagne de la Seranne.
Pendant la descente, l'équipage de l'A 320 aperçoit le G 103 et effectue une
manœuvre d'évitement par la droite. Le bord d'attaque de l'aile gauche de l'A 320
et l'extrémité supérieure gauche de l'empennage du G 103 se heurtent. Les deux
appareils se posent sur leur aérodrome de destination.

L'extrémité arrière gauche de l'empennage du G 103 est arrachée.
Le bord d'attaque du bec n°4 de l'aile gauche de l'A 320 est enfoncé et déchiré.

English translation:

The Airbus A320, with destination of Montpellier-Méditerranée Airport, was authorised to descend to flight level 80.  At the same time, in local flight around Saint-Martin-de-Londres airport, the G103 glider rose to 8600 feet in a climb above the Séranne massif.  During the A320's descent, its crew spotted the G103 and executed an evasive maneuver to the right.  The leading edge of the left wing of the A320 and the upper left extremity of the empennage of the G103 collided.  Both craft landed at their destinations.

The rear left end of the G103's empennage was torn off.
The leading edge of slat #4 of the A320's left wing was dented and torn.


Would putting several small propellers on a wing be efficient?

It would provide pretty good STOL performance at low speed because there is a significant increase in lift with the wing in the slipstream of a propeller, especially with flaps down.  One of the biggest differences between a jet and a turboprop while flying a landing approach is that power settings have a direct effect on sink rate with a turboprop where a quarter or a third of the wing span is in the propeller slipstream; not so much on a jet.

Then when you speed up, the inefficiency of all those draggy nacelles and relatively inefficient smaller propellers, the weight, the maintenance nightmare, the fuel burn.  Yikes.  That's why it's not done.

There's a reason that airplanes are all built to a few near-universal configurations.  They are the arrangements that hit a sweet spot, in the balance of compromises game, for the airplane's mission, and they are timeless until some major new paradigm comes along.  That's not one of them.


Why do jet engine igniters require huge voltages?

In short, 40 kV isn't that much voltage for applications that are intentionally creating an electrical arc. Car spark plugs also use voltages in the tens of thousands of volts for the same reason, for example.
As for why that is:
In general, air acts as an electrical insulator. That is, electricity won't pass through air at normal voltages. Which is good because otherwise you'd have a constant arc to ground through the air from any exposed hot conductor and that would cause lots of problems.
As with any insulator, air has a dielectric strength, measured in volts per unit distance. For a given length of air (such as the spark gap in a spark plug,) there exists a breakdown voltage at which point the voltage differential per unit distance exceeds the dielectric strength. When a voltage equal to or greater than the breakdown voltage is applied to conductors on either side of said length of air, the air will suddenly ionize, creating a channel of plasma through the air. The plasma channel now has a much, much, much lower resistance than air normally has, allowing current to flow across the gap and quickly equalizing the potential (i.e. voltage) on each side of the gap.
As you're likely aware, plasma tends to be quite hot. The plasma channel created by the above process is the visible arc that you'll see between the conductors in a spark plug.
For air at normal pressures, the dielectric strength is about 3 MV/m. That is, if you want to create a 1-meter arc, you'd need 3 megavolts of potential across it. Or, in units more suited to creating ignition sparks (which are hopefully not a meter in length,) you need around 3 kV per millimeter. So, for example, in the winter when you take off a fleece coat and then experience a shock the next time you get close to a grounded conductor, the static potential that has built up on you is about 3 kV per millimeter (i.e. 30 kV/cm or around 75 kV/inch) of the maximum length of the arc you can create to such a conductor.
So, in summary, 40 kV really isn't all that much when you're trying to create arcs through air, especially not highly pressurized air, such as in a piston or jet engine. Even relatively small distances require quite high voltages in order to arc. Which is a good thing so that exposed conductors don't just constantly create arcs to ground. Or to grounded people, electronics, etc.
By the way, this ability of an electric field to ionize air is why switches for very high voltage transmission lines have to have much, much longer poles than what you'll find on normal switches. On a 138 kV line, for example, the electricity would simply arc across a switch that created a gap of less than couple of inches or so when open. Perhaps an even larger gap when humidity is high. And these switches do indeed arc while opening and closing. They can also create quite long arcs while opening, since the plasma channel is already in place. Here's an example of what that can look like at 138 kV:

Of course, in this case, you have a more-or-less continuous voltage source, not just a stored-up charge that is suddenly released, so the arc won't just be a brief flash, but will continue until the distance between the conductors becomes too high to maintain the arc.
And, of course, when the potential between the base of a cloud and the ground gets too high, you get lightning. And, yes, that's a very, very high voltage to arc across a kilometer or more. According to the U.S. National Weather Service, a typical lightning bolt involves potentials of around 300 MV. While that actually seems a bit low to arc across the typical distance of a lightning bolt, lightning normally occurs in thunderstorms where the atmosphere is already very humid and, thus, more conductive than normal.

As far as the ease of igniting jet fuel, while that's mostly unrelated to the voltage required to create a spark across a given distance of air, it's actually not that easy to ignite. At standard air pressure, you can drop a lit match in a bucket of jet fuel and it will just extinguish the match. You can also create a raging fire in the fuselage of a Boeing 777 and the fuel remaining in the tanks of said 777 won't burn. This is by design and it's one of the great things about jet fuel for aviation. While the energy density and specific energy of petroleum fuels is very high (by chemical reaction standards,) it actually requires quite high temperatures and/or pressures to ignite jet fuel, making it an ideal fuel for providing lots of energy per unit weight while not tending to randomly burn or explode at inconvenient times.


What is meant by a "congested area of a city/town/settlement" in FAR 103?

I could not find a definite definition of congested area.

As mentioned here:

  [...] neither the FAA nor the NTSB has ever provided [...] a precise
  definition of [...] a "congested area." Rather, a "congested area" is
  determined on a case-by-case basis. According to the Board, "the
  determination must take into consideration all circumstances, not only
  the size of an area and the number of homes or structures, but, for
  example, whether the buildings are occupied or people are otherwise
  present, such as on roads."

The same is echoed here:

  [For the definition of congested area,] FAA and the NTSB have opted
  for taking a "case-by-case" approach in determining how to apply
  certain terms.

AOPA states that:

  Congested areas. "Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of
  1,000 feet above the highest obstacle within a horizontal radius of
  2,000 feet of the aircraft." The FAA does not define congested area in
  the FARs or in the Aeronautical Information Manual. Interpretations in
  low-flight enforcement cases are not consistent for purposes of
  drafting a precise definition. Such a determination is usually decided
  on a case-by-case basis, and in the cases that we've seen, congested
  has been interpreted rather broadly. For example, a highway with
  moderate traffic was found to be "congested," as was a seaside area
  where 200 to 300 persons were sitting on the beach or bathing in the
  water.

The same can be seen here, and here, and here.


Could in flight folding wing tips lead to a safer airliner design?

A few issues make fold-up wing tips unfeasible:

Weight and complexity of a mechanism and control system for it.

Shifting CP forward makes the airplane less stable statically. In any case, if you want to reduce trim drag, just move the C of G aft to unload the tail to get the same result, and use computers to artificially induce static margins, which is already done.

The stall speed reduction from the extra wing area is quite small.  A wing tip that added  10% to wing area when dropped would only drop the stall by a few knots.  The stall speed reduction from adding flaps dwarfs the reduction you get from adding area.

At high altitudes, you want the extra span so you wouldn't want to retract the tips anyway.  On an airliner that cruises sub-sonic at high altitudes, there's no benefit to reducing span.  On sub-sonic airplanes, where you clip off the wing tips, it's to improve speeds at low altitudes (like the clip wing Spitfire, done to improve performance below 20000 ft - for the very high altitude versions used to take on JU-86s, they added span).

The only practical reason to have folding wing tips on an airliner is to reduce span on the ground, as an alternative to winglets (which are used to gain some of the benefit of added span without taking up space or adding to bending loads on the wing), but a winglet is a much cheaper solution.

Which, as always, is why you haven't seen anybody do folding wing tips in the last 60 years, whereas winglets are everywhere.


What you saw is called a speed brake, which is one of the functions of the spoilers. From the Boeing 737 NG FCOMv2 (9.20.5 Flight Controls - System Description):

  Flight Spoilers

  Four flight spoilers are located on the upper surface of each wing. Each hydraulic
  system, A and B, is dedicated to a different set of spoiler pairs to provide isolation
  and maintain symmetric operation in the event of hydraulic system failure.
  Hydraulic pressure shutoff valves are controlled by the two flight SPOILER
  switches.

  Flight spoiler panels are used as speed brakes to increase drag and reduce lift, both
  in flight and on the ground. The flight spoilers also supplement roll control in
  response to control wheel commands. A spoiler mixer, connected to the aileron
  cable-drive, controls the hydraulic power control units on each spoiler panel to
  provide spoiler movement proportional to aileron movement.

  The flight spoilers rise on the wing with up aileron and remain faired on the wing
  with down aileron. When the control wheel is displaced more than approximately
  10°, spoiler deflection is initiated.

  Speed Brakes

  The speed brakes consist of flight spoilers and ground spoilers. Hydraulic system
  A powers all four ground spoilers, two on the upper surface of each wing. The
  SPEED BRAKE lever controls the spoilers. When the SPEED BRAKE lever is
  actuated all the spoilers extend when the airplane is on the ground and only the
  flight spoilers extend when the airplane is in the air.

  The SPEEDBRAKES EXTENDED light provides an indication of spoiler
  operation in-flight and on the ground. In-flight, the light illuminates to warn the
  crew that the speed brakes are extended while in the landing configuration or
  below 800 feet AGL. On the ground, the light illuminates when hydraulic pressure
  is sensed in the ground spoiler shutoff valve with the speed brake lever in the
  DOWN position.

You noticed that the spoilers did not extend as much in the air as on the ground. This is intentional to reduce buffeting:

  In-Flight Operation

  Operating the SPEED BRAKE lever in flight causes all flight spoiler panels to rise
  symmetrically to act as speed brakes. Caution should be exercised when
  deploying flight spoilers during a turn, as they greatly increase roll rate. When the
  speed brakes are in an intermediate position roll rates increase significantly.
  Moving the SPEED BRAKE lever beyond the FLIGHT DETENT causes
  buffeting and is prohibited in flight.

The speed brake lever must not be moved above the FLIGHT DETENT while in the air. You can see it in the following image from the FCOM:

To answer your other questions:

  If it is brake, do an airplane need brake in the air?

Yes, sometimes. Ideally a flight profile is calculated that does not require the use of brakes in the air. That means the Flight Management Computer (FMC) calculates a so called Top of Descent point at which you can start an idle descent. So the engines are retarded to idle thrust and the aircraft maintains the target speed by descending. This will get you on final approach at the desired altitude. Two things can happen now:

Air traffic control does not allow you to descend when you want to. This usually happens when there is conflicting traffic and you have to stay at a higher altitude than the idle descent profile for a short while. Afterwards you need to descend faster, which may require the use of speed brakes. You can also try to just increase the target descent speed (since higher speed means more drag and gets you down faster), but if that is not enough speed brakes are needed.
Air traffic control gives you a shortcut. This happens quite a lot. Some Standard Terminal Arrival Routes (STARs) involve some complex maneuvers and turns, but if traffic allows you can get a shortcut. Now your distance to the airport has just been reduced, requiring a steeper descent. Again, use of speed brakes helps here, especially when you are close to the airport already because below 10,000 ft you have to maintain 250 kt or lower, so speeding up is not an option.

  If it is brake, is not more efficient to reduce the engine's power rather than to keep it constant power but brake to make it slower?

The engine will already be reduced to idle on a normal descent profile. Therefore using less power is not an option any more. Use of reverse in flight is usually prohibited for most aircraft, e.g. 737 FCOM:

  Intentional selection of reverse thrust in flight is prohibited.