How does induction ice form in and affect jet engines?

Induction ice can be a problem for jet engines. Other answers have explained how the ice forms. The air expands and cools in the inlet before entering the engine. The first stages of the compressor do not compress the air enough yet to warm it enough to prevent ice from forming. Low power settings can also make it easier for ice to form. Certain atmospheric conditions make ice more likely to form.

The FAA released AC 20-147, which "provides guidance and acceptable methods, but not the only methods, for demonstrating compliance with the applicable engine induction system icing and engine ice ingestion requirements." This describes different types of icing, and the effects it can have on engines. It also describes how engines should be tested to conform to the regulations for these conditions. Ice can form in various places:

The fan or compressor blades themselves
Vanes
Sensors
Bleed ducts

This ice can cause various problems:

The ice can come off and damage engine components downstream
The ice will reduce the effectiveness of blades, making it harder for the engine to compress the air
The ice can impede the flow of air in the engine
The ice can block sensors, preventing the control system from correctly monitoring the engine, which can lead to power loss or instability

One form of icing that has been an issue lately is ice crystal icing. This is caused by small ice crystals in the upper atmosphere, particularly above convective clouds. The FAA has issued an AD (Airworthiness Directive) recently about this.

  This type of icing does not appear on radar due to its low reflectivity, and neither the airplane ice detector nor visual indications reliably indicate the presence of icing conditions. Therefore, it is often undetected by the flight crew. Flight in these conditions can cause ice crystals to accumulate in the core gas flow path of the engine.

There were previous events on GE CF6-80 engines (used on 747, 767, A310, A330, and others) that the FAA looked into.

  In the events leading to those prior ADs, the ice has shed during throttle transients and in the descent phase of flight, causing temporary thrust loss.

However, there have been incidents with the newer GEnx engines on 747-8 and 787 aircraft which have been more serious.

  The new events that prompted this AD, however, have occurred during the cruise phase of flight and caused permanent damage (beyond maintenance manual limits) to the engine compressor. In all thrust loss events, data indicate that ice crystals entered and collected in the initial stages of the compressor. Engine temperature data indicate small ice accretions were shed through the core of the engine.

The engine manufacturers are working to resolve the issues on the aircraft currently affected, and in the meantime flight crews are advised to avoid weather conditions where ice crystals tend to form.

  More definitively, the AD includes immediate mitigating procedures for the affected aircraft which prohibit flight within 50nm of amber and red radar returns that are displayed below the aircraft’s flight path during operations at or above 30,000 ft, when approaching, or in, IMC or visible moisture.

  Note: Boeing has also published an updated Flight Crew Operations Manual Bulletin with specific operating procedures for flight crews.


How do I make consistent landings from the (instrument-less) backseat?

Since nobody else has posted an answer, I follow Dan's suggestion and copy my comment here. Unanswered questions make this site look bad.

Practice, practice, practice. It's for a reason that the pilots who fly consistently good landings are the older ones. And remember where the horizon is in reference to the airframe and how the engine sounds. At approach speed (= at high angle of attack) the aircraft will show large attitude changes for small airspeed changes. Remember how high you are at conspicuous points along the approach, don't be shy to look sideways for this. And keeping a little throttle makes better landings, so don't feel negative about this.


How much fuel do the new A320-Winglets burn vs. the B737-800?

Airbus says this about their new blended winglets (aka "Sharklets"), being fitted to new A320s, and retrofitted:

  Airbus’ next step is the large Sharklets™ wingtip devices, representing another element in the ongoing continuous improvement programme for its best-selling A320 Family. These devices improve aerodynamics, reducing fuel burn by up to 4 per cent – which amounts to annual savings of more than 900 tonnes of CO2 per aircraft.

Given that an A320's fuel burn rate is approximately 5.13 gallons per seat per hour, reducing this by 4% gives you 4.92 gallons/seat/hr.

Comparatively, a 737-800 burns about 4.88 gallons/seat/hr.

Source:

  A 737-800 burns 4.88 gallons of fuel per seat per hour, compared with the comparable A320's burn of 5.13 gallons per seat per hour, according to The Airline Monitor, an industry publication.

So they're near enough the same.


What are the length requirement for US aircraft N-Numbers / registrations?

It's not just small aircraft in the US - all aircraft with US registration follow the same rules. The FAA has guidelines on how an N number must be formed. Basically, there are relatively few limits - you can have N + up to 5 characters, up to 2 of which can be letters (at the end).

Here's what the FAA has to say:

  U.S. registration numbers may not exceed five characters in addition to the standard U.S. registration prefix letter N. These characters may be:

  One to five numbers (N12345)
  One to four numbers followed by one letter (N1234Z)
  One to three numbers followed by two letters (N123AZ)

  To avoid confusion with the numbers one and zero, the letters I and O are not to be used.

  Other Requirements

  An N-Number may not begin with zero. You must precede the first zero in an N-Number with any number 1 through 9. For example, N01Z is not valid.
  Registration numbers N1 through N99 are strictly reserved for FAA internal use.

When an owner registers an aircraft, they can request an N number, provided it's not already registered.


What types of antennae do aircraft have and what are their functions?

The Boeing 787 has just about every kind of antenna I can think of. Here's a chart of all their locations and purposes.

From Boeing 787 Systems Manual


How much efficiency gain can be attributed to aircraft handling?

In a paper written in 2010 several factors are laid out in addition to aircraft design that have improved fuel efficiency and cost over the years and possible improvements in the future. Several areas were highlighted.

Routing

Opening up more airspace by more efficient usage increases efficiency.

  It is estimated that up to 8% of all aviation fuel is wasted as a result of the inefficient routes aircraft have to fly.

The paper cites flight management systems on newer aircraft as contributing toward efficiencies in routing.

  On certain oceanic routes, flight control computers are automatically plotting their own, most efficient routings with some impressive results. One airline, for example, has been working with Australian air traffic management to save almost 10 million litres of jet fuel and 772 hours of f light time in five years. It does this by exploiting the jet streams and tailwinds in the Indian Ocean.

The following charts show projected savings for implementation of NextGen air traffic systems in the US and SESAR in Europe.

Continuous climb

Being able to climb continuously to cruise altitude can save on fuel.

  A number of airports and airlines are trialling the use of so-called ‘green departures’, allowing pilots to take-off and climb to the optimal cruising altitude in one smooth, continuous ascent. This is   in contrast to the traditional method of climbing to the cruising altitude in several steps. By using this new departure method at one airport alone, some 10,000 tonnes of fuel and 32,000 tonnes of carbon dioxide were saved in one year alone.

Continuous descent

Similarly to climbing, fuel can be saved by avoiding stepped approaches.

  In trials, fuel savings of up to 40% during the approach phase have been demonstrated. This equates to between   CDO [continuous descent operations] vs stepped approach 50 and 150kg of fuel depending on the level at which CDO is commenced and the aircraft type. Up to 150,000 tonnes of fuel a year, or 500,000 tonnes of CO2, could be saved in Europe alone if CDO approaches were more widely adopted.

Satellite based approaches and departures

Using RNAV procedures help expedite aircraft through the airport environment.

  Using satellite-based and on-board precision navigation systems such as “Area Navigation” and “Required Navigation Performance” capabilities allows ANSPs [Air Navigation Service Providers] to re-design airspace and procedures so aircraft can fly automatic fuel-saving routes into and out of the busiest airports in the world. These new departure routes have reduced departure delays of more than 2.5 minutes per flight at one airport since their introduction. Annual fuel savings are estimated at $34 million, with cumulative savings of 105 million from 2006 through 2008.

Ground handling

Fuel is saved by using single engine taxi or tugs where appropriate.

Another place more efficiency can be garnered is by installing ground electrical power to reduce APU usage.

  studies suggest that up to 85% of APU use can be reduced if groundbased electrical power systems are available, cutting the fuel bill, per gate, by $100,000 a year.

Reducing delays

Another costly problem is flight delays. Aircraft end up sitting on the ramp or taxiway burning fuel waiting for clearances.

  In the United States alone, the cost of burning fuel on the ground as a result of delays to the airline schedule amounted to over $5 billion in 2008 alone.

Conclusion

The following graph represents the potential fuel savings projected into the future broken down by technological improvements in aircraft design and fuels, operational issues such as ground handling and delays, and infrastructure such as airspace availability and routing. Of course any future projection is speculative.


Are there any simulators around to simulate ADS-B data (TIS-B & FIS-B)?

Aeroflex IFR-6000
From the manufacturer's website:

The Aeroflex IFR 6000 is a compact, lightweight and weatherproof unit designed for testing transponder modes A/C/S, TCAS I and II as well as DME. Includes antenna shield and hard transit case. The IFR 6000 features an extremely easy to use interface where every parameter the user commonly needs to view is displayed on screen.
Dedicated Mode keys for XPDR, DME and TCAS allow quick selection of the operational mode. The application dependent softkeys and data select/slew keys provide an intuitive man machine interface. DME mode is provided with dedicated keys for frequency/channel selection and RF level control.
For frequently varied parameters in DME and TCAS modes, such as Range and Rate, dedicated keys are provided. Each operational mode has one main user screen. The operational modes are: XPDR (Sub-Modes: ADS-B MON, ADS-B GEN & GICB) DME TCAS 1, 2 (Sub-Modes: TIS) Most tests can be completed without leaving the main user screens. This simplifies the line technician's testing task.

However, it is subject to stringent export restrictions. If you are outside of the US, it is not available to you.


How can a person receive an expired life vest?

You can buy aircraft life vests pretty inexpensively for the purpose of having one or seeing how they work.

There are a bunch of used ones for sale on eBay, they may have been taken from planes over the years or they may just find their way into circulation after being removed (before being trashed).

Some of them get upcycled/recycled into other things so they presumably enter circulation at some point.


Why are Israeli planes followed by an armored police truck at ZRH?

It is happening as an extra security measure, probably attempting to mitigate the risk of an explosive-laden person or car breaching the perimeter fence - like many city airports ZRH has a multitude of roads running around the perimeter fence which cannot all be manned 24/7. Is it mostly for show? Who knows!
There has always been more risk associated with flying to Israel - anyone who flew there pre-9/11 was not surprised by the extra security measures added to all flights post-9/11 as they had been dealing with them since forever.
It seems that American might also get the same treatment at Zurich based on a photo here: https://www.airliners.net/photo/American-Airlines/Boeing-767-323-ER/531127/L


In the US, what can be done at an airport when volunteering hours?

Commercial airports are challenging for volunteers because of security, if you want to do anything beyond the security barrier (ie where the interesting stuff is) then you need to be cleared and supervised, and that costs time and money.

There may be opportunities at small airports, which don't have the same security concerns. Most won't have any established volunteer positions, it would be more of a case of talking to the airport manager or someone running an FBO and asking if there's anything you could volunteer for. Ask politely, wait a few days, then follow up with a phone call, if they know you're genuinely interested (and polite, sensible, not likely to run into a propeller) they might be willing to offer something to you.

One last thing, if anyone asks you to get a bucket of propwash it's an old aviation joke.


Is flying a UAV via a VR controller (e.g. Oculus) legal in the US?

According to Model Aircraft Operations one of the requirements for flying a model aircraft is:

  Keep the aircraft within visual line of sight at all times

If you are wearing a VR headset, then your visual line of sight stops at the headset screen.

Note that the above linked page lists the "visual line of sight" as a safety guideline. However, according to Section 336, an aircraft is not considered a "model aircraft" unless it is:

  (2) flown within visual line of sight of the person operating
  the aircraft

None of the above restricts you from flying with a friend where one of you is wearing the VR headset and the other is piloting the aircraft.


What is the height of the Boeing 747-8 landing gear?

In general, the landing gear height is defined as the distance between the ground and the conjunction between main gear strut and the aircraft structure (fuselage, wing, nacelles, etc.).

The landing gear height of any aircraft varies depending the loading conditions and where you measure it (nose or main landing gear). This info is from the 747-8 Airplane Characteristics for Airport Planning document by Boeing.

Image from 747-8 Airplane Characteristics for Airport Planning by Boeing

Here, 'E' gives the height of the (main) landing gear attached to the fuselage.


Would it be possible to economically repair 9V-SWB?

As far as I know, the damage has been categorized as "substantial", meaning that it will be costly, but the aircraft has not been written off.

I would expect that the wing will be completely replaced (thus it will not be cheap), but given the current status anything more is speculation (and what I wrote already is).

Update: the aircraft was returned to service on 12 Nov 2016.


Minix wingtip vortices mitigation - How does it work?

The tiny mass of air that this device can affect will in no way have the claimed effect on induced drag. This wingtip vortex pseudoscience is just bullshit. What can be observed as a vortex behind the wing is actually the consequence of the vortex sheet rolling up due to downwash behind a lift-generating wing. But air flowing around the tip has almost nothing to do with it.

I would compare it to those magnetic rings you are supposed to put around your fuel line to save fuel. Snake oil, in other words. There is no way this thing can reduce the wing's vortex, all it will do is to create some more local turbulence.

All it needs is a slick salesperson, a few gullible people with too much money and greed, a big promise, and the scam takes its course. This can easily yield enough investment money to allow all scammers to drive a Ferrari for a year or more. Now they have a year to come up with the next big thing.


Is there a reason or code behind the Cessna model numbers?

There is no theme, but like some cars or mobile phones, there's a logic to it. A higher series (200 vs. 100) is bigger, a higher sub-series (180 vs. 170) is more powerful, the P and T are pressurized and turbo, and so on.

The no theme is supported by the Apr 1981 issue of Flying Magazine, where it is confirmed by the Marketing SVP of Cessna (p.58).

Re: what about the last digit, e.g., 180/182/185?

"Engineering numbers" mean internal numbers with no marketable meaning, just like the first two digits. My guess is that there were 181, 183, and 184 designs on paper at one time.


Puzzled by this question I did my own research and found numbers that allows to get a good comparison for year 2016:

According to the United States Parachute Association (USPA), there were 3.2 million jumps in 2016 and 21 fatalities. Therefore, the chances of dying in a single jump were 1 in 152,381.

For a comparison with driving, we can use data from the Insurance Institute for Highway Safety. According to which, in the United States there were on average 1.16 deaths per 100 million vehicle miles traveled.

Crunching those numbers, the chances of dying by driving one km are 1 in 138,103,448. Therefore, to equal those chances to one skydive you have to drive 906 km.

Summarising

In 2016, a single skydiving jump in the US represented the same risk of death as driving 906 km (566 miles).

[UPDATE] Demographics

Many have pointed in that there might be an important component of the risk related with age, experience and how careful a skydiver is.
To approach to an understanding in that regard I've compiled the 147 fatal accidents in the USPA database that happened from 2008 as a result of solo jumps (i.e. not-tandem).
This data do not allow to infer real demographics trends, because I don't know how many total jumps were in each demographic group (I only know how many lead to a fatal accident). However, the visualization of some aspects of the data can be informative.

In the following figure each dot is a fatal accident, and it is plotted based in the numbers of jumps the person involved have performed before the accident (vertical axis) and the age of the person (horizontal axis).

It is clear that the bulk of casualties happen to fairly experienced skydivers (100+ jumps). So, as expected, the more you jump the more chances of dying you have. Note that the vertical axis is logarithmic (so to distinguish between people with relatively small jump counts).

This may lead to think that the first 100 jumps are quite safe, but we can not jump to that conclusion: If you check how many death are there for different jump numbers, you have the following picture

In this plot, the first bar counts deaths during jumps 1 to 50, the second bar for jumps 51 to 100 and so on.
So now it seems that most deaths are in the first 50 jumps. However, that  does not mean that the first 50 jumps are more dangerous, because there were many more jumps corresponding to jump number 1 to 50 than jumps number 900 to 950. So, however informative, this have no real statistical value. And the trend suggesting that jumps become less dangerous as you gain experience might be just an artifact due to the fact that there are more beginner skydivers than experienced ones.


What would happen if put a jet engine behind another jet engine?

There is an alternate way to answer your question, and it relates to thermodynamics.

Think about the purpose of a jet engine.  It exists to take uncompressed air, compress it, mix it with fuel, burn it efficiently and then expand it (hopefully adiabatically) to generate a larger volume of gas at higher pressure than the intake.  The work done by the engine is described by the Brayton cycle (Figure 3.13 from http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node28.html), and this cycle shows us where we can and can't hope to achieve theoretically efficient operation.

If you look at the chart of the cycle in the above reference, you'll note that the compression and exhaustion portions of the cycle are where inefficiency (in the form of entropy) creep in and prevent the cycle from being perfect.  As such, even if there were sufficient oxygen left to burn, putting two jet engines back to back would be horribly inefficient (because you are repeating the inefficient portions of each twice).

The better solution is to work towards improving compression ratios, and recovering more work from expansion.  Much of this has been done over the last 50 years, and is why Brayton efficiencies are in the 0.6 to 0.7 range for modern jet engines (ref same website, Figure 3.19).

EDIT: Also, remember that jet engines are designed to work on air that is "cold" relative to their exhaust. They don't compress hot gases efficiently. You could certainly design a compressor to efficiently compress hot gases for combustion, but jet engine compressor sections are not designed for this, so the compression achieved by the second engine in your question would be MUCH lower than its design, which would further decrease it's contribution of additional thrust.


What does ATC mean when they refer to "company"?

Generally when used in ATC movement instructions the word "company" means "The other aircraft operated by your company".
In this context it's a convenient shorthand for controllers and pilots: If two aircraft from the same operator are going to the same place on the airport (one may be told "Follow company"), or to assist with visual separation and sequencing on approaches.

In other cases it can mean "the airline (company) you work for" (such as being instructed to taxi to a ramp and "call company for your gate assignment" - the distinction is made based on the context of the request or instruction).

Note that this is not standard phraseology: despite being widely used the term company does not appear in the pilot/controller glossary or the Air Traffic Controller's Handbook .


When departing from a class C or D airfield, what is the proper VFR procedure?

Either C or D controllers will likely accept your requested heading, which can be given as a rough compass point, on initial contact. This contact will be after picking up the terminal info on ATIS, when you contact ground.  Your preferred direction will be passed up the chain.  A class D may tell you something like "cleared for takeoff, Northbound departure approved", in which case I would feel free to turn as soon as I deemed it safe.  In a class C scenario, the same thing could happen, but they might vector you around other traffic.  In all cases "resume own navigation" will be permission to take your heading.

If you are still on runway heading and feel you have not been given a clearance sending you where you want to go, you may contact tower or departure control, depending on whom you are with, and say something like "Tower, Diamond two-eight bravo, request heading zero six zero"  They may respond with an "approved as requested" or "heading zero six zero approved" or they may give you instructions to "fly present heading, I'll call your turn" indicating they are not ready for you to take your heading yet.

The short answer is, you can take your heading when you have been cleared to do so.  Understanding when you have been cleared is a matter of becoming familiar with standard phraseology.

Controllers I have worked with, especially at C and D airspaces have been accommodating.  Their job is to send pilots where they want to go while keeping aircraft out of each other’s way.  They have rolled along with me when I have changed my mind about landing,  I can say "I changed my mind, I'd rather depart the pattern to the south" but to be brief I'll say "Cancel landing intention, request south departure."  As airspace gets bigger and controllers are busier (which can vary by location and even time of day) brevity becomes increasingly important.  To get practice, you can find out when an particular airspace is less busy.  Controllers have been known to be chatty when traffic volume is low, and you may even be able to ask questions about preferred phraseology.


Why are the A300/310’s electric pitch trim switches inhibited with the autopilot engaged?

Like with two human pilots, you want control1 to be explicitly in one hands. With autopilot, it's the same: it should be either autopilot or you.

In the case of 'breaching' the normal transfer protocol for whatever reason ("I have control" - "You have control", which in case of autopilot would be the autopilot disconnect button), there are two possible courses of action when the pilot just starts to control the aircraft:

Immediately give control by explicitly disconnecting the autopilot.
Keep control by ignoring/overriding the pilot as much as possible.

Apparently, Airbus espoused the second strategy. It made sense for them to ignore the pilot (whether for trim or main control) until s/he explicitly requests control. (There is not much the aircraft can do when the pilot starts to trim the wheel manually, so it still disconnects).

If the trim switches were not ignored, there could be two options.

Disconnect the autopilot. But this changes the whole ideology, and other things would need to be changed to be consistent.
Just change the trim. But the autopilot (which is still in control) would have to fight against it in order to keep doing its job (e.g. flying level), either by trim or elevator.2 This makes no sense and creates dangerous confusion.

Arguably, completely ignoring the pilot is not a very good idea, so Airbus had to change the algorithm at least in some situations.

1 By 'control' I mean guidance control, excluding things like stability augmentation systems.

2 Unless this is a simple autopilot which does not actuate trim at all and may then need help from the pilot. This is the case for some GA aircraft, but not for A300/310.


Why do modern airliners have only two engines?

Engines are expensive, maintenance-intensive and heavy. You only need 2 to keep a large plane in the air.

In the days of the 747 regulations required at least 3 engines if you ventured more than 60 minutes of flying time away from a suitable diversion airport (in case the second one also failed). However as reliability of engines increased this got extended with ETOPS certificates.


Can self-study and FSX substitute for the majority of PPL training?

Unfortunately, no.

If you learn and practice and master the flying skills in a flight simulator, you will become a certified pilot only for that simulator, not for real life.

You didn't mention the country, but you can look at this answer to find all the requirements to become a private pilot in USA.

Using a flight simulator, you can learn many very valuable skills which will be very useful in your actual flying (and many many pilots do a lot of practice in a simulator), but in no way it can completely replace actual flying. There are many things you can only feel in actual flying experience. You can make any mistake in a simulator and no harm is done, but not in actual flying.

Everything in flying is expensive. Even after you get your PPL, you still have to pay for flying afterwards. Since you are young enough not to have chosen a career path yet (probably), why don't you try to become an airline pilot?

For the answer to your second question, a few topics are:

the airplane and its physics
its engine
weather
effects of weather and altitude on pilots
navigation
planning
... and many other topics

There are tons of material available covering these topics. FAA has a wide array of reading material which you can download for free.


Do airports have their own incident/accident investigation departments?

More often than not, the accident investigation boards in Europe are a governmental unit independent of NCAA. The Board should be able to criticize and put requirements on all units involved in an accident/incident. This obviously include the CAA.

Departements and organizations are free to do an accident investigation. Availability to an accident site may be limited, though.
E.g. IFALPA have a structure of their own Accredited Accident Investigator, available for any relevant investigations.


Is night VMC still VMC if the underlying terrain is completely unlighted?

The short answer is no, the definition of night VMC does not specifically require any defined degree of ground illumination to be present.  (at least in the US)

You raise some excellent concerns in your question, demonstrating a solid understanding of the principles of Operational Risk Management:  Identify the hazards, assess the risk, make decisions, implement controls, and monitor.

Following these steps prior to, and during night flight is crucial to safety for the reasons you describe.  As long as visibility is relatively clear and there is enough ground lighting to form a discernable horizon, flying on even the darkest nights can be done safely, and can actually be fun.  It is easier to pick out other aircraft visually, and roads and cities really highlight themselves.  In areas where illumination is sparse, situational awareness of your position and the highest terrain in your sector is crucial.

It is rare for anybody to truly need to fly VFR at night, so if weather, visibility, ground lighting, or any other conditions are concerning to you, either don’t fly, or file IFR if you are so rated.


What regulations govern the quality management system for producers of aircraft components?

From FAA, Production Certificate:

  A production certificate is an approval (document) to manufacture
  duplicate products under an FAA-approved type design (e.g., type
  certificate or supplemental type certificate). The holder of a
  production certificate may obtain an airworthiness certificate for
  aircraft produced under the production certificate without further
  showing. To obtain one, the production application and approval
  process must be followed.

See also:
Production Approval - Regulations & Policies (link).


Is it OK practice to use one altimeter on QFE and one on QNH (local flight, dual altimeters)?

I would turn it the other way around. Assuming the Dynon EFIS is your main flight instrument I would dial in QNH or QNE (depending on your altitude). Common practise is to always have the second altimeter set to QNE (1013.25hPa; 29.92inHg) but if you do not need an altitude reading in Flight Levels it's fine if you set up one altimeter to QFE.

But remember: Even using this practise you HAVE to change the settings. QFE and QNH are both depending on the local pressure and therefore change pretty often. If you are on a cross country flight you then have to change both altimeters to different settings in order to have a correct altitude and a correct height readout.

Also make sure that you always use the same altimeter for altitude and the other one for height so you won't use faulty values from the wrong altimeter!


Can hours at an FAA flightschool be credited to an EASA PPL?

Assuming that "flight school hours" means flight time then CAP 804 suggests yes:

  3.6 Logging of Flight Hours gained in the USA   Some flight hour recording practices allowable in the USA do not comply with European
  and UK requirements. In particular:

  2 pilots flying together in a single pilot aircraft both claiming P1    hours;
  One pilot accompanying another on newsgathering or traffic    control flights and claiming P1/PIC when they have not acted as Captain or signed for the aircraft.

  Flying hours of this nature cannot be credited towards the
  requirements for Part-FCL or UK Licences.

The last sentence implies that if hours logged in the US do comply with "European and UK requirements" then they can be credited towards licenses. If you need something more detailed and explicit then it may be easiest to ask the CAA directly.


What does a white diagonal line mean on an Airbus ECAM DU?

Display Management Computer issue:

  If a DMC fails, all information is removed from the displays it
  controls and replaced by a white diagonal line to indicate a working
  display with a failed source. ECAM will detect the failure and provide
  a sequence of alerts.

  Due to the priority rules, the E/WD display will
  move to the lower DU if it was DMC1 that failed. The EIS DMC switch is
  used to replace the failed DMC with DMC3.

Source

Steps to clear warning:

  First select DMC #3 to isolate fault to DU or DMC. If DMC is at fault
  reset above associated circuit breaker for 5 seconds. If fault is with
  DU reset these (CAPT PFD/ND = G3/E1) (FO's PFD/ND = R3/R4) (Upper ECAM
  = E5) (Lower ECAM = R11).

Source

More in the maintenance manual at AMM31-60-00-710-001. (EIS start).


Are lhe old King KX170B Nav/Com radios monaural?

Yes. The idea of listening to anything more than scratchy AM radio via your ADF was an alien concept in the 70s, unless you had some custom system made up for you.  It's really only taken off since ANR headsets have made it quiet enough within the earcups to make music worth listening to.

You just need to get a mono-to-stereo jack adapter to hear the mono signal in both ears.


What are the consequences of touching down at too low of a speed?

This is certainly not a comprehensive answer but can get you started. I’m assuming fixed wing non-VTOL aircraft.

A low (forward) speed touchdown, all other things being as close to nominal as possible in that scenario, translates in all likelihood to a steeper than normal landing and can be associated with loss of sufficient lift or even stall and can result in a hard landing or crash. If trying to compensate for loss of lift, the same scenario will lead to a higher pitch than normal and thus add (or replace the above with) a tail strike risk.

A low vertical speed touchdown, all other things being as close to nominal as possible in that scenario, means a shallower trajectory than normal and can be associated with a long flare or a deep landing and as such poses risks around stopping performance (e.g. if the touchdown is so soft that the automatic deceleration systems don’t even realise the aircraft is on ground) or available stopping distance (if all the runway is used up trying to stick the aircraft down, none is left for rollout). Exiting the runway down the far end at substantial speed again is a recipe for significant damage and danger for life.

A touchdown with both (too) low forward and (too) low vertical speed doesn’t really exist, as that would mean a touchdown roughly along the nominal path but with lower speed, and since approach speed is usually calculated to be somewhere around minimum safe speed (i.e. stall speed plus some margin), slowing down significantly means stall, at which point the scenario changes to low forward but high vertical speed at touchdown.


What is the difference between reversible and irreversible controls?

Reversible is when there is a direct linkage from controls to control surfaces. For example the cable linkages in a light aircraft up to an MD-80.

Irreversible is when there is a hydraulic power control unit in the way, it can be mechanical or fly-by-wire. And such controls would sometimes need an artificial feel system to relay how much force is being applied.

It is found in airplanes that cannot be steered by just muscles.

A good way to picture it, is what happens if you move an aileron by hand, would the yoke turn as a result or no. Superman might be needed for a 747's rudder, but still, the rudder pedals won't budge.

More information here and here.

Source: airlinebuzz.com

Photo shows an unpowered rudder that was swung by the wind, in the cockpit the rudder pedals would show the neutral position, hence irreversible.


There is no US regulation about whether an airport can be called "international." The Secretary of the Treasury designates the official list of international airports of entry. But not all airports on this list are even called international, and it does not include all airports with international flights. There are even some airports called "international" with no customs facilities or plans to have them in the near future. The airport name is determined by the airport owner.


What airport has this walkway over a taxiway?

This image was taken at London Gatwick. The bridge connects two portions of the North Terminal, right next to where the North Terminal is labeled on this map:

London Gatwick claims to be the first airport to have such a feature. As can be seen in the photo, it is the largest in the world, high enough for a 747 to pass underneath.

This is not the only airport to have such a feature, though. Denver International also has a bridge (picture) over the taxiway connecting the terminal building with Concourse A. This one is not as high as the bridge at Gatwick and can't clear anything larger than a 737.


Why is landing on a carrier not handled by a computer?

Computers can, in fact, control the approach of a Super Hornet all the way to touchdown.  However, there are limits to the sea state. Gross deviations in glide path resulting from a pitching deck would make a coupled approach impractical.

However, the most compelling reason to hand fly all our approaches is that we fly a $60 million jet. Murphy's Law tells us that the most junior guy, with the least experience behind the boat, is going to get an engine fire, at night, in rough seas.  If our fictional JO wasn't proficient hand flying the ball behind the boat this could result in catastrophic consequences including both the loss of aircrew and aircraft. As often as possible, we prepare for the 1 percentile, not the 99th percentile, so when we do get that engine fire at night we get the upgrade OK, and not the cut pass/ ejection.

Plus, its just plain eerie letting the jet fly itself to the boat, and the current system isn't reliable enough that most guys would feel comfortable letting it fly itself on a regular basis.

Edit:  Heck, new guys aren't even allowed to perform auto approaches (auto throttle) to the boat for the same reason.


How were pilots selected and trained before the introduction of simulators?

Almost every pilot learns to fly in an actual aircraft, this is one of the reasons all trainers have dual controls.

My first day out, ever, was in an actual plane, behind real controls, in the sky. No sim-time prior to that. The instructor talked me though takeoff and maneuvers (keeping an eye on everything and operating the rudder). All he did was radio coms, navigation and the approach/landing.

As for whats common:

The vast majority of American WWII pilots are said to have learned to fly in the piper J-3 Cub

The Boeing PT-17 Steraman and AT-11 Kansan were also popular.

In GA where everyone else gets their start the Piper Cherokee and Cessna 150 or 172 rule supreme.

Of course these planes are slow, benign and fairly safe by aviation standards. But what if you have some super fast, one of a kind, high flying, awesome supersonic jet gadget. You surely cant afford to ruin such a plane but still need to train pilots. Well in that case you just build yourself a dual cockpit custom trainer....

Even the space shuttle had a real flying trainer designed to mimic its approach characteristics.

All that being said simulators can be a big help if used properly.


Is corrected astigmatism disqualifying for an EASA Class 1 medical?

I have a registered astigmatism on one eye that is balanced by the other eye. I have a Class 1 medical w.o. problems. In my medical record, the Doc wrote that my astigmatism corresponds to a .75 dpt on one eye.

He also told me that absolute values are not important, important is that the astigmatism is corrected by either the other eye, some glasses or it is so low that the brain can even correct for it.


How frequent are unpublished holding patterns outside general aviation?

Not very frequent at all.

The need to delay traffic toward an airport is quite common. Usually, it is simply a question of fitting someone in a sequence of arriving aircraft, but there can be more severe cases, such as a runway change or ongoing emergency. In any case, ATC has a number of tools to use, and unpublished holdings are usually one of the last tools to be selected.

What we usually prefer to do is make use of radar vectoring instead. This is much more flexible, easier to work with and requires less time on the frequency. A normal holding pattern takes 4 minutes to fly. If needing to delay a flight for just a few minutes, using a holding will only really work if it works to delay the flight 4, 8, 12 etc. minutes. If I need to delay someone 6 minutes to fit in an arrival gap, then I could put them in a holding for 4 minutes and then vector them around for 2 minutes, but if I am going to be giving delaying vectors anyway, skipping the holding is easier.

On a busy radio frequency, available time on the frequency is everything for a controller. Nonessential or long messages can really ruin your day when working a tight approach sequence into a busy airport. Let's look at the phraseology for instructing an aircraft to enter a non published holding that the crew were not expecting:

  SAS123 proceed direct to ANDIE, alpha november delta india echo, and hold. Inbound track 120, right turns 1 minute legs.

Depending on your rate of speech, such an instruction may take almost 10 seconds to issue (and you can't just speak faster, because then the pilots will ask you to repeat yourself because they missed something).

If ATC needs to delay flight for a long time (say, more than 10 minutes), then holdings can definitely be an option, but in that case published holdings are used as much as possible. Published holdings are designed to ensure terrain clearance down to a specified lower limit, and, importantly from an ATC perspective, have defined lateral separation minima to other traffic. We are not allowed to use radar separation to aircraft established in a holding, so separating traffic from someone holding in a non published holding would be quite a hassle - but for published holdings, holding areas are defined, to which we can use radar separation. Finally, the phraseology for entering a published holding is much shorter:

  SAS123 hold over ANDIE as published.

If ATC needs to delay a flight for a short time (say, less than 10 minutes), using radar vectors is usually much easier, both for the controller and the crew. It is much more flexible (I can vector people around, and start creating a sequence 50 miles from the airport, even though there is no room near the airport yet) and can be used to delay flights any number of minutes (not just multiples of 4). And the flight crew just needs to adjust their heading, no need to calculate holding tracks, compensating for current wind and so on.

Of course there are cases, for example emergencies, where pilots may request to hold somewhere that does not have a published hold, and ATC will of course permit them to do so. But looking at the workload establishing a non published holding gives us, using a published holding or some other tool (radar vectors) is usually the preferred option.


How to recognize the horizontal winglet in the Horten design, or the experimental glider in this video?

You can't from the planform alone.

First, winglets are no magical device. Calling the wing with bell-shaped lift distribution one with horizontal winglets tries to free-ride on the mystique that NASA marketing has created around the winglet. But the physics behind it are rather mundane and the thrust which is created by the outer wing is a bit of payback for the higher losses at mid-span from a steep lift gradient over span.

Next, all wings create thrust if you define it narrowly enough. This comes from the suction force on the forward upper side of the airfoil and is called leading edge thrust.

Induced drag is the backward tilt of the aerodynamic forces and is caused by lift creation. The least amount of drag for a given amount of lift and wingspan can be achieved with the elliptic distribution over span. The bell-shaped distribution creates more drag for the same lift and wingspan, since it has higher spanwise lift gradients at mid-span.

  What is it that makes the end of this wing a winglet?

This is a matter of definition. The so-called winglet area is where the wingtips carry only little positive or even negative lift. Like in a winglet, this gives the local lift a forward component which works like the opposite of induced drag. Call it induced thrust, if you want: This is what is common to winglets and the negatively loaded wingtip. That in turn is caused by wing twist and local control surface deflection. You cannot see from the top view how lift is distributed over span.

But the bell-shaped lift distribution has some interesting advantages:

Since most lift is created near the wing root, the spar bending moment can be kept low for a given amount of lift. This allows for a lightweight wing structure and is especially important for large aircraft.
With aileron deflection, the lift distribution on the up-going wing becomes nearly elliptical while the one on the down-going wing becomes even worse, increasing induced drag there significantly. This reduces adverse yaw such that no vertical tail is needed.

Sounds great, doesn't it?

Actually no, it doesn't when you take a closer look:

Due to the low maximum lift coefficient of flying wings, the wing surface of a flying wing needs to be much higher than that of a conventional configuration of the same landing speed where a tail surface allows the use of powerful trailing edge flaps, raising wing weight and drag substantially.
The bell-shaped lift distribution is like flying all the time with spoilers half deployed. Aileron deflection retracts the spoiler on the up-going wing and extends it fully on the down-going wing. Kind of like the split ailerons of the B-2. I think it is better to only use spoilers during manoeuvring. Also, the Horten flying wings were all known for marginal directional stability, especially at high speed when sweep did not help much. It was too little to even compensate for unsymmetric thrust. A fin or added artificial stabilization would be highly advisable.


Is a ground station radio license required for UAS operations in the US?

Air -> Air, or Ground -> Air describes the ultimate path of the message. It doesn't describe what's being discussed. So:

  The communications would concern a sUAS in the air, but the radio is physically on the ground.

If the radio endpoints are both on the ground, then that's ground -> ground transmission. Put it another way - if a controller talks to a fireman over the radio, about an aircraft in the air, it doesn't magically become a Ground -> Air transmissions.

The definition matters primarily for technical and practical reasons (E.g.., Air -> Air radio will have a better range than Ground -> Ground because of nothing being in the way). If you're on the ground, you're a ground station - it's as simple as that.


What is the range of pressures a space shuttle can withstand?

The Shuttle Crew Operations Manual has basic information which might answer your question. Starting on page 799 (section 4.3) you'll find Airspeed Limitations.
During ascent the dynamic pressure limit is 819 psf. The limit is based on thermal protection constraints, rather than other structural concerns.
During entry, the dynamic pressure limit varies by velocity. The limit is based on stability (controllability) constraints.

During a Return to Launch Site (RTLS) abort, the allowed limits were a bit higher:

Page 1002 has a graph showing typical Ascent dynamic pressure:


What is the relation between the EASA Light Aircraft Pilot Licences and the Private/Sailplane/Balloon Pilot Licences?

LAPL (Light Aircraft Pilot License) can be a pathway to a PPL (Privat Pilot License) but can also be just kept by it's own, as it's somewhat cheaper to get and maintain than a PPL.

LAPL has stricter limitations than the PPL, for example they are only valid in EASA countries and not in all ICAO states. Also, LAPL is limited to a maximum take-off weight (MTOW) of 2000kg and does not have the options of upgrading to IFR or similar (Night VFR is an option though) and a maximum of 4 people on board (3 passengers + you).

Therefore: If you are fine with the mentioned limits, you're good to go for an LAPL. If at some point you want to upgrade to PPL, thats not a big issue as it just requires the additional training hours (theory is the same for LAPL and PPL).


Which are more efficient in putting out wildfires: planes or helicopters?

Both have their respective uses. A fixed-wing carries far more water (3,200 gallons or 12 tons for the Be-200 vs 100-700 gallons for helicopters), but takes more local infrastructure to operate, and is more difficult to discharge exactly where you want it. A helicopter is more precise, but carries less water. A heli is quicker to load up and discharge near the water, but a fixed-wing flies faster, so is better suited to delivering water or a custom mix a longer distance away.

You want both, not just one. You'd use helicopters to suppress smaller fires if possible before they get out of control, attack larger ones at specific spots, and fixed-wings to lay down longer lines of fire retardant against developed wildfires. Larger helicopters also support fixed-wings in this. Which is "better" if you could only have one kind... that's not so much an aviation question as a fire-fighting one.

As for cost, helicopters are normally less cost-effective, being far more expensive to operate per ton-mile. A large aircraft is more expensive in absolute terms. Being smaller and less demanding of the infrastructure, helicopters can be stationed in a more critical location and react more quickly.

It's not a worse/better question, it's tools for the job. Fixed-wing fire-fighting aircraft are more specialized, with their internal water storage, while fire helicopters can be as basic as a light utility heli carrying a water bucket.


What do FAA DERs require regarding low-level requirements in DO-178C?

One thing I would start with is that low level requirements are not the same as derived requirements, although low level requirements can be derived. Derived requirements are requirements that cannot be traced to a higher level requirement.

For verification of DO-178C Level C software, your SVCP will need to completely cover high level and low level requirements as well as attain 100% statement coverage of your code.

As far as what the DER for your project will approve, there really isn't any way for us to know.


Does the sound barrier apply to a silent aircraft?

The sound barrier has nothing to do with the noise the aircraft makes. It has to do with the fact that if it is going fast enough the air can't get out of the way. This creates a shock wave where the aircraft is pushing the air aside. A shock wave is where the speed of the air transitions from faster than sound to slower than sound and involves the release of considerable energy. You can control the shockwave to some extent by careful shaping of the surfaces, but a plane going fast enough can't be silent.

You can make very quiet sub-sonic aircraft, but they tend to go slowly so that the noise of the air flowing over the craft is minimized.


Are sequenced waypoints still displayed on the Navigation Display / FMS legs page?

Previous waypoints are not shown on the 787's CDU, and only the last waypoint or PPOS (present position at which a direct-to was initiated) shows on the ND.

The 787 EFB does not show the plane position. Only very recently the FAA allowed own-ship display on moving maps.

As to why, there is no use for it. The POS REPORT page on the 787 would show the three waypoints needed for position reports (from, to, and next).

Some airways are one-way, so it's not like a U-turn will be needed (there is also no reverse sequence function). Any emergency gets priority and a direct-to the nearest suitable airport (weather and terrain permitting).

If the whole plan is needed (on display) for some reason, it can be reloaded as a secondary inactive route (if saved, or if can be requested via uplink).

On the MD-11, the progress page shows the last waypoint (singular), but not the 787, so minor differences can be expected. Above applies to the 787's route legs and progress pages.

Source: 787 FCOM.


Why would Boeing be under review if crew-error is determined to be the cause?

In aviation (and other safety critical areas) it's not enough to just look at the first cause of an accident, you have to look at why that mistake was made, and why that thing happened, as far back up the chain as you can. Then you try to address all the problems.

So, when a pilot makes a mistake, it's tempting to say "the pilots was an idiot. Case closed." However, then you've got to wonder why the company employed idiots, and how many  others are flying. That implies that there's something wrong with the pilot licencing and testing rules, and that has huge implications.

If we assume that these pilots weren't idiots, we have to ask why they made a mistake, because other good pilots could make the same mistake. Anyone who has played a computer game knows that mistakes are inevitable when you're under enough stress, just like a well built bridge will still break if it's overloaded.

You could conclude that they hadn't been trained well enough, which raises the question "Why?". Apparently the pilots did all the required training, so maybe the training was at fault. But it's not enough to just improve that piece of training, you've got to ask why again. Was it not checked? What else hasn't been checked properly? How do we know that any future training will be properly checked? Also, what incentive did the person writing the training have to miss things out, and does it apply elsewhere?

If you don't find and fix the root of a problem, it will continue to grow until it pops out somewhere else and causes another tragedy.


Is the time spent flying in a Sailplane concidered a valid flight hour for a LAPL / PPL license?

In the UK, under the CAA (and as a CVn mentions, it may vary across EASA land, regardless of SERA), these are the rules:

  The privileges of your licence will only remain valid if you have
  completed, in the last 24 months, as pilot of an aeroplane or TMG:

At least 12 hours flight time as PIC, including 12 take-offs and landings; and
Refresher training of at least 1 hour of total flight time with an instructor.

That document also explains that:

  A LAPL for aeroplanes will allow you to act as pilot in command (PIC)
  on two classes of aircraft: either a single-engine piston aeroplane
  (land) or touring motor glider (TMG) with a maximum take-off mass of
  2000 kg or less, carrying a maximum of 3 passengers, with no more than
  4 persons on board.

So I think that, in the UK, you can't act as PIC on a sailplane and so can't count any hours toward your LAPL

However, TMG flying is very cheap, if you can find one for hire


It did!
You can see a bit of it here

or in the reflection here

And here it is from the exterior


Can I leave my smartphone turned on in the checked-in luggage?

Your phone must be in airplane mode whether it is in the passenger cabin or cargo hold.  In this case the phone will never establish a 3G connection and won't meet your desired use case.

Leaving the phone with cell service on will likely also not solve your problem.  Cell phones tend to use a lot of battery trying to connect to a tower when there are none in range.  By the time you land your phone may have already shut down from losing power.  If the bag is lost it may be deep in the bag handling areas of the airport or some other corner with no cell service and certainly no GPS signal.  In all likelihood unless someone mistakenly takes your bag home and decides to charge your phone and turn it back on this plan of yours will not work.


Why do we use composite aluminium or titanium stacks in airplanes?

I've boldfaced the parts of this abstract that answer the question.

  Abstract: Ever since the advent of fiber reinforced polymer materials in the field of Aerospace, Metal-FRP stacks started to gain importance due to their superior fatigue performance, phenomenal low weight and good specific strength. However the machining, specially drilling these multi stack materials has always proved to be a challenge ... The very properties that make the FRP composite superior make it a challenge for machining. The mechanism of machining viewed here is more or less fracturing and breakage of the fibers present in the system. This breakage of fiber also induces fractures in the tool resulting in accelerated tool wear. These characteristics render the process unreliable. Also the temperature during the machining of composites is higher than while machining a metal due to the lower thermal conductive properties of the composite. When two such extremely different elements are brought together in the form of a FRP-Metal stack, various challenges are faced to achieve required hole size, quality, tool life, ...

-- Peter Mueller-Hummel, Prithvi Sripathy, and Abdelatif Atarsia, "Fail Safe Drilling of CFRP/Titanium and /Aluminium Stack with H8 Quality for Aerospace Applications," SAE International, 2013.

Cutting speed, cut depth, and feed rate depend strongly on the particular stack's composition: which metals, which composites (carbon, aramid, fiberglass), their ratio, each layer's thickness.

Metal/composite stacks are used all over an airframe.  The 2011 article "A review: Fibre metal laminates, background, bonding types and applied test methods" by Sinmazçelik et al calls them FML's, fiber metal laminates, and figure 3 from there shows where they're found on the Airbus A380:


Are there any aircraft that either fold or employ folding in their design (such as with origami)?

My favourite is probably the Nikitin-Shevchenko IS which could morph between biplane and monoplane by folding its lower wing up into the upper one. The lower wing had two hinges on each side, one at the root and the other at about one-third span, so its outer section was indeed double-hinged.

Does it count to do something similar but cruder and simply let the upper wing go once you have taken off? This slip-wing was trialled on the Hillson Bi-mono before being fitted to a Hurricane.
The Tu-144 airliner and Dassault Mirage "Milan" had retractable "moustache" canard foreplanes which they deployed to improve takeoff and landing performance. Being tailless deltas, they had limited scope for conventional flaps, so put moustaches at the front instead. The moustache of the TU-144 was quite complex, having full-span flaps which amounted to a variable-camber aerofoil, so their trailing sections provide another rare example of genuine double-movement.
The XB-70 Valkyrie folded its wing tips down during Mach 3 cruise, to improve stability and waverider lift. The A-12 variant of the Blackbird was one of a small handful of types to have had a more prosaic ventral fin which folded up for landing and takeoff.
The Wild Goose and Swallow projects of Barnes Wallis at Vickers deserve mention, although they only flew as sub-scale test RPVs. They were examples of what he called the "wing-controlled aerodyne", having swing-wings in place of conventional control and tail surfaces. Not so much a double-action as eliminating the double-action of control surfaces on a swing-wing by using the whole fuselage as one giant multi-functional control surface (a tip he picked up from his work on airships such as the R100).
Does sliding count? The Akaflieg Stuttgart fs29 sailplane has telescoping wings which can pull in to increase cross-country speed. A few other experimental types had them too, such as the Makhonine Mak-10. The Gérin Varivol had a more complex variation on the theme, with a full-span high-aspect-ratio fixed section, which supported leading- and trailing-edge sections that were stowed in the fuselage and scrolled out along the wing like lowering a Venetian blind.
Polyhedra are solids with flat surfaces. Folding them using origami techniques is quite an art form, so I make no apology for the next example. Most polyhedra assemble rigidly but some, known as "breathing" polyhedra, can flex to a limited extent. An example from aviation is the variable-thickness wing experimented with by Rocheville among others, which bulges its top surface upwards to provide high lift for takeoff and landing, then draws it back down to create a thin wing for high-speed flight.


Are there regulations for the field of view from cockpits?

The certification specification for aircraft are deliberately a bit vague on the topic. This allows manufacturers to come up with creative solutions that may have been prohibited if specific angles where required in the specification.

For large aircraft, EASA has requirements CS25.773 in the Certification Specification 25 (CS25) PDF which is included below this answer. The FAA requirements are similar in FAR 25.773.

To make sure that there is an agreed standard on what is acceptable to the certifying authorities, acceptable means of compliance have been published. Manufacturers may deviate from the AMC's if they have good arguments for it.

An example of the FAA AMC on this topic can be found in AC25.733-1 (PDF).
The FAA document refers to standard ARP 4101/2 which is the successor of SAE 580B (unfortunately you have to pay for these documents).

From this answer and the image there contained, you can see how the outside visual field of view of the cockpit of the A320 family compares to the 580B standard.

  CS 25.773 Pilot
  compartment view (See AMC 25.773)  a) Non-precipitation conditions.
  For nonprecipitation conditions, the following apply:

  (1) Each pilot
  compartment must be arranged to give the pilots a sufficiently
  extensive, clear, and undistorted view, to enable them to safely
  perform any manoeuvres within the operating limitations of the
  aeroplane, including taxiing, take-off, approach and landing.

  (2)
  Each pilot compartment must be free of glare and reflection that could
  interfere with the normal duties of the minimum flight crew
  (established under CS 25.1523). This must be shown in day and night
  flight tests under non-precipitation conditions.

  (b) Precipitation
  conditions. For precipitation conditions, the following apply:

  (1)
  The aeroplane must have a means to maintain a clear portion of the
  windshield during precipitation conditions, sufficient for both pilots
  to have a sufficiently extensive view along the flight path in normal
  flight attitudes of the aeroplane. This means must be designed to
  function, without continuous attention on the part of the crew, in –

  (i) Heavy rain at speeds up to 1·5 VSR1, with lift and drag devices
  retracted; and

  (ii) The icing conditions specified in Appendix C and
  the following icing conditions specified in Appendix O, if
  certification for flight in icing conditions is sought (See AMC
  25.773(b)(1)(ii)):  (A) For aeroplanes certificated in accordance with CS 25.1420(a)(1), the icing conditions that the aeroplane is certified
  to safely exit following detection.

  (B) For aeroplanes certificated
  in accordance with CS 25.1420(a)(2), the icing conditions that the
  aeroplane is certified to safely operate in and the icing conditions
  that the aeroplane is certified to safely exit following detection.

  (C) For aeroplanes certificated in accordance with CS 25.1420(a)(3),
  all icing conditions.

  (2) No single failure of the systems used to
  provide the view required by subparagraph (b)(1) of this paragraph
  must cause the loss of that view by both pilots in the specified
  precipitation conditions.

  (3) The first pilot must have a window that:

  (i) is openable under the conditions prescribed in subparagraph
  (b)(1) of this paragraph when the cabin is not pressurised;

  (ii) provides the view specified in (b)(1); and

  (iii) gives sufficient
  protection from the elements against impairment of the pilot's vision.

  (4) The openable window specified in sub-paragraph (b)(3) of this
  paragraph need not be provided if it is shown that an area of the
  transparent surface will remain clear sufficient for at least one
  pilot to land the aeroplane safely in the event of -  (i) Any system
  failure or combination of failures, which is not, Extremely Improbable
  in accordance with CS 25.1309, under the precipitation conditions
  specified in sub-paragraph (b)(1) of this paragraph.  (ii) An
  encounter with severe hail, birds, or insects (See AMC 25.773(b)(4)).

  (c) Internal windshield and window fogging. The aeroplane must have a
  means to prevent fogging to the internal portions of the windshield
  and window panels over an area which would provide the visibility
  specified in sub-paragraph (a) of this paragraph under all internal
  and external ambient conditions, including precipitation conditions,
  in which the aeroplane is intended to be operated (See AMC 25.773(c)).

  (d) Fixed markers or other guides must be installed at each pilot
  station to enable the pilots to position themselves in their seats for
  an optimum combination of outside visibility and instrument scan. If
  lighted markers or guides are used they must comply with the
  requirements specified in CS 25.1381.

Many aircraft have eye position gauges in the cockpit that pilots can use to adjust their seat for optimal view. They either try to line up little colored balls or look through a small sight. Here are a few examples:

Airbus A320

Image Source

Cessna Citation

Image Source

ATR-72

Image Source

McDonnell-Douglas MD-80

Image Source


How is one's hypoxia resistance affected by the time of day?

As noted by others here, PPL course questions might not be designed according to pure deductive or inductive reasoning. My approach would have been the following:

Medical-related aviation questions tend to base their background on "old" studies, so let's have a look at Van Liere, E. J. (1964). Resistance to Hypoxia. Archives of Internal Medicine, 113(3), 418.:

  As a corollary, it would be anticipated that if the metabolic rate of
  an animal were elevated, the ability to withstand hypoxia would be
  decreased. Zarrowetal in 1951 demonstrated that hyperthyroid states
  decrease tolerance to hypoxia. The thyroid-stimulating hormone (TSH),
  thyroxin, and dinitrophenol all decrease hypoxic resistance.

TSH has a circadian rhythm (24 hour cycle) and levels peak between midnight and 6am (refer to https://medicalsciences.stackexchange.com/a/4034/15791). Therefore, 3am and 12am are not an option, which leaves us with 5pm.

I'm aware that you stated that the correct answer is 3am, and I'll definitely check back with my medical colleagues on that, but the question in itself is clearly not well-defined within the visible context on this platform.

As others mentioned, one measure of gauging the depression of cellular oxidation is metabolic rate, for which in 2014 according to Examining Variations of Resting Metabolic Rate of Adults: A Public Health Perspective no single value for RMR is appropriate for all adults.

Last but not least, if we talk about hypobaric hypoxia, conclusions change again.


Is a monobloc variable incidence wing viable (updated)?

Yes it is a viable way for roll control - aerodynamically that is. The mechanism you describe is a proper servo tab, where the aeroforces on the tab are fed back, and the tab acts like a lever on the main control surface. This was the way the post WW2 airliners were controlled, before they got too big and fast and only hydraulics could do it.

However, as usual, an aerodynamically beneficial solution has some serious structural drawbacks. An aerobatics plane can do 6g and the wings must be seriously strong and resistant to bending and warping. Normally, a wing has two spars which form a torsion box with the upper and lower skin.

If this torsion box can extend from wing tip to root, it is a strong and light construction. But if it has to be cut somewhere and the two wing halves are to be connected by a hinging rod, that spot will be a weak spot in the wing. It can be made strong enough, but the real problem is wing stiffness.


How does cabin pressure vary with respect to ambient pressure during descent?

During descent, the rate of change of pressure inside the cabin of a pressurized aircraft is lower than outside (ambient).

Inside the aircraft, under active control the  cabin pressure increases from equivalent ~8000ft above sea level to ground level. In the meantime, the aircraft descends from cruising altitude which is typically much higher, also to ground level.

Assuming the pressurization and descent start and end roughly at roughly the same time, the cabin is necessarily pressurized slower than the increase of air pressure outside in absolute terms  (e.g. psi per minute) assuming a steady pressurization profile .

Corner cases arise when the airport is at an elevation above 8000ft or so since the cabin will be further depressurized during descent. So while the relation holds in absolute magnitude , they will be of opposite sign. (until there is an airport  24,000 ft or so....)


Can a private pilot placard an inoperative instrument?

The answer to your question is probably. The rule governing this is

  §91.213   Inoperative instruments and equipment. (a) Except as provided in paragraph (d) of this section, no person may take off an
  aircraft with inoperative instruments or equipment installed unless
  the following conditions are met:

and if you skip past the MEL section (which, as you noted, doesn’t apply to most small general aviation aircraft) you see the conditions that must be met.

  (3) The inoperative instruments and equipment are—

  (i) Removed from the aircraft, the cockpit control placarded, and the
  maintenance recorded in accordance with §43.9 of this chapter; or

  (ii) Deactivated and placarded “Inoperative.” If deactivation of the
  inoperative instrument or equipment involves maintenance, it must be
  accomplished and recorded in accordance with part 43 of this chapter;
  and

  (4) A determination is made by a pilot, who is certificated and
  appropriately rated under part 61 of this chapter, or by a person, who
  is certificated and appropriately rated to perform maintenance on the
  aircraft, that the inoperative instrument or equipment does not
  constitute a hazard to the aircraft.

Suppose your landing light burns out. A landing light is not required unless you are flying for hire, so you can put a piece of tape under the switch and label it Inoperative and you are good to go.

If your transponder fails, turn it off and mark it Inoperative. If you are going to fly in airspace that requires a transponder, you have to jump through some hoops per §91.215, but you are still good.

If there is something that requires removal or disabling—and it is not something you are allowed to do in Part 43—then you need an A&P to remove or disable it and make a logbook entry. I’m having a hard time thinking of something that would need disabled and yet you could still legally fly the airplane. The best I can come up with right now is a stuck push-to-talk button. That’s not listed in Part 43 as something that you can perform maintenance on, so an A&P would have to disable it and make a logbook entry.

By the way, you can fly forever with inoperative equipment. There is a LORAN in plane I fly that has been marked inop since they decommissioned LORAN. When I put a new radio in my plane 10 years ago, I kept the old one in case something happened to the new one, and marked the nav portion inop.


What is the typical touchdown angle of a large airliner?

(Source: 744 FCTM)

The relevant text reads:

  Airplane body attitudes are based upon typical landing weights, flaps 30,
  VREF 30 + 5 (approach) and VREF 30 + 0 (landing), and should be
  reduced by 1° for each 5 knots above this speed.

  Typical landing flare times range from 4 to 8 seconds and are a function of
  approach speed.

  Initiate the flare when the
  main gear is approximately 30 feet above the runway by increasing pitch attitude
  approximately 2° - 3°. This slows the rate of descent.

So for one of the largest, a delta of 2-3° is achieved in 4 to 8 seconds. As the text shows, the attitude varies based on speed, flaps, etc., so we can take the delta as both the optimum and typical value.

I checked the 777-200 FCTM, the values are different. And of course the smaller the plane, say a 737, the later the flare is initiated due to the smaller [and later] the ground effect.


What is the effect of sudden extreme temperature change on brake disks of large aircraft?

The temperature changes from altitude to ground are not (usually) rapid. Therefore the possible sub-zero to red-hot case is not as severe as may be thought. If carbon discs are the example, they require temps that are almost beyond steel discs braking capability.


Do small aircraft have sockets for passenger headsets?

The rear seats of a Cessna 172 has headset jacks, I imagine the 182 has the same.

You can see them in this picture:

Image source

You might also find them over the shoulder of rear passengers - as can be seen in this image (copyright attached)

That links the rear-seat passengers to the same intercom you're used to from a front seat passenger.


How do Airbus and Boeing aircraft handle Dutch roll?

This is quite similar to the other question you asked.

From my knowledge as a flight simulator enthusiast I can summarize the following:
Boeing aircraft in the past used to be controlled pretty much direct pilot with cables running through the aircraft to control hydraulic actuator valves that power the flight control surfaces. The rudder is usually augmented with a yaw damper system which measures the yaw rate and roll rate, the rudder input and aileron input can “calculates” the desired rudder deflection to dampen the yaw rate and dutch roll. This can be as simple as performing a weighted sum on the yaw rate, roll rate, rudder input and aileron inputs with some factors that may depend on airspeed. The yaw damper(s) can be turned off with a switch in the overhead panel and are relatively simple in design. Easy to test fully and certify easily.
When the autopilot is on it manipulates the flight controls directly, i.e. moves the yoke with mechanical actuators. Thus, the yaw damper doesn't even have to know about the autopilot state in this case.

On Airbus planes and more modern fly-by-wire Boeing aircraft the flight control computers are fed with the pilot inputs and the computers then send signals to the actuators electronically by wire. The controls laws within these computers can be quite complex and usually also incorporate the autopilot control modes.

With full control over all flight surfaces the computers can manipulate individual control surfaces perfectly to remove any undesired motions. E.g. in the A320 the aileron and elevator computers constantly evaluate the current pitch and roll rate against the target rates. Any deviations (e.g. caused by a yaw rate) are immediately countered by aileron, spoiler or elevator inputs. With that alone the Dutch roll already can no longer exist. The roll is already stopped because of the roll feedback loop.

But it doesn't stop there. The flight augmentation computers receive information about the deflections of ailerons and spoilers for example and then can perform internal flight model computations to figure out how much rudder they need to compensate the adverse yaw for example. Or how much aileron will be needed when to stop the Dutch roll as we add rudder deflection. The computers also take the desired turn rate into account and also have inputs such as the balance indicator to fully coordinate the turn to create a slip free turn with close to no side forces on passengers and pretty much zero Dutch roll.

The flight control systems can be almost arbitrarily complex as you add more and more features into it. E.g. when you have an engine failure the computers could also receive inputs from the engine N1 differences and compute the necessary rudder deflection to prevent any yaw from asymmetric thrust. The A380 even goes as far as to use split ailerons on the opposing side of an engine failure to create artificial drag on one side to increase the counter torque. But it can also use ailerons strategically to dampen any oscillations within the wing to create a smoother ride experience. Now you're not only controlling a rigid aircraft, you start to take wing flex into account.

To answer the second question: The yaw damper can be a separate system with parts like asymmetric thrust compensation or other higher level functions just being turned off in case of a computer failure. This way the yaw damper can be used in a more basic control law even if there are mayor failures in other systems which helps control the aircraft in abnormal situations.

Since the yaw damping itself is sort of the last instance before the rudder actuator it doesn't need to be an integrated part of the wider system but the higher level functions will need to be computed somewhere within the control computers. Both implementations probably exist.

... sorry for the long post :)


Why did Cessna get rid of manual flaps in their 172?

Nobody can definitively answer this for you except Cessna's 1965/1966 engineering team (the year they made the change), but there are two reasons I can think of:
Because switches are cooler than Johnson bars; or Because everyone else is doing electric flaps.

Much like with manual transmissions, some people just don't like the extra work of manual flaps, and for those folks electric "flip a switch and don't worry about it" flaps are a selling point.

In terms of reliability it's a trade-off (as are all engineering decisions), so let's look at a few of the factors:

Mechanical Flaps

+Flaps still work when the battery is dead.
+The pilot can control the extension/retraction rate to some extent.
+Usually cross-linked with a bar (so you can't have a "split-flap" condition)
+Simple to rig, adjust, and maintain.
-Actuation requires more pilot skill
You need to develop the muscle memory to grab the handle without looking.
You need to learn to govern the extension/retraction rate smoothly.
-The failure mode is usually "Flaps Up"
You could lose your flaps on short final if the cable or lock mechanism fails.

Electric Flaps

+"Easier to Operate" (you don't need to reach down to the floor)
+Extension/Retraction rate is constant (governed by the motor)
+Fewer moving cables running through the fuselage (wires replace them)
+Typical failure mode (e.g. dead battery) is "Flaps stuck where you left them"
Less chance of losing your flaps on short final.
+Depending on the design they may save some weight over a mechanical system.
-You lose control of the flaps if the battery dies (no-flap landings are more likely)
-You have one or more motors to maintain/replace if they fail
-Depending on the design it's possible to have a "split-flap" condition

Cessna's engineers and marketing folks looked at those factors (and probably many others) and decided that electric flaps "made sense". On the other side of the GA fleet, Piper's engineers looked at the same factors and decided to keep the Johnson bar flaps (which are still found in the PA-28 series today).

From a manufacturing standpoint it makes sense for all of the aircraft a manufacturer produces to use the samecontrol mechanisms -- either all the planes use mechanical flaps or all the planes use electric flaps because it simplifies production and allows everything to run through on one assembly line rather than stopping at the flaps and diverting aircraft to different teams.


How to calculate the Pitching moment coefficient of wing?

Take the pitching moment coefficient of the wing's airfoil at the trim angle of attack. Since the reference area normally is the wing's area and the reference chord is the wing's mean aerodynamic chord, you do not even need to adjust the number. I hope you have the airfoil polar at hand; if the wing uses several airfoils, take a volume-weighted average; volume being here the product of local area and chord. If the wing has a symmetric airfoil, the coefficient is zero, in most other cases it will be a small negative number.


Why are the stabilised approach criteria different for an instrument approach and a visual approach?

All instrument approaches are not alike. The Flight Safety Foundation Approach-and-Landing Accident Reduction Tool Kit, Section 5.1 — Approach Hazards Overview points out

Fifty-three percent of the accidents and incidents occurred during nonprecision instrument approaches or visual approaches (42 percent of the visual approaches were conducted where an instrument landing system [ILS] approach was available); …
Fifty-nine percent of the accidents and incidents occurred in instrument meteorological conditions (IMC); …

For a precision ILS approach, the ALAR recommends additional criteria in that the approach must be flown within one dot of the glideslope and localizer.
The thousand-foot gate is clearly driven by the worst case of a circling approach where the aircraft is not aligned with the runway, must transition off instruments back to visual flying, make the appropriate maneuvers, and land safely. Those all take time, so we should expect the recommendation to be at least as high as the visual approach.
In Section 7.1 — Stabilized Approach, we read

In addition, a stabilized approach provides

More time and attention for monitoring ATC communications, weather conditions and system operation;
More time for monitoring and backup by the PNF;
Defined flight-parameter-deviation limits and minimum stabilization heights to support the decision to land or to go around; and
Landing performance consistent with published performance.


What pitch attitudes are common during an emergency descent for an airliner?

My experience was on the Regional Jets but from sim training I recall that the pitch down once at Vmo with flight spoilers extended was somewhere around 10-15 deg.  The standard procedure for the CRJ was to declare "emergency descent", slam the thrust levers to idle, flight spoilers fully out, dial the Autopilot altitude preselect to 10000 ft, select the Autopilot to Speed Mode, and dial the speed select to Vmo, and just let the airplane do its thing while the two of you went through the QRH.
You will get a small G reduction during the pushover, but the AP would pushover gently enough to avoid making people in the back float around.  If you push over manually, there is a risk of pushing too hard in the stress of the situation and banging heads against the ceiling in the back (it doesn't take much when you're going fast like that).
Any G reduction that occurs is only momentarily during the pushover.  Once up to speed you are back to 1 G more or less. The pitch attitude in the descent would be noticeable to a passenger looking out the window from the slanting horizon, but I don't think it would look like they were diving straight at the ground.  The scarier part would be the rumble from the spoilers being out, and the roar in the cabin from flying at Vmo.


Severe convection will have anvil tops at the tropopause and overshooting tops can penetrate much higher (severe thunderstorm warnings often use a value of 60,000 ft for threats to aircraft).  How high the overshooting tops can get is a balance of the positive buoyancy during parcel ascent against the negative buoyancy once it gets into the warming stratospheric air.

A U2 could overfly these storms, but most aircraft are not designed for stratospheric flight (due to the temperature increasing with height in the stratosphere) and any commercial aircraft will be unable to go over these storms.


Is this an accurate method to showing how the correct Decision Altitude/Height for an approach has been determined?

This is USA information. The summary: determine the obstacle clearance surfaces, add the required obstacle clearance buffers to those surfaces, adjust DA for glide slope angle and aircraft speed if not already above the minimum due to obstacle clearance. The procedures are all calculated in true altitude, not indicated altitude. Aircraft that fly IFR in the USA are required to have adjustable precision altimeters based on the ISA atmosphere and barometric altimeter based approaches must have a local weather station that provides the altimeter setting for that airport. The difference in DA based on temperature is not considered significant, however there are low temperature limits placed on baro-vnav approaches due to effects on glide path [not DA].
A typical DA in the USA is determined without altimeter temperature adjustments because a DA is only used with positive vertical course guidance, a three degree slope is the same at any temperature. There may be be a fixed decision-altitude adjustment calculated when a remote weather source must be used, based on potential difference in pressure. There may also be a low temperature limit in some cases for procedures that allow uncompensated baro-vnav systems because this equipment can change the glide path angle.
While there were some old manual calculation standards that could be simplified into the answer you are looking for, the modern method is calculated by computers using rather complex algorithms with multiple intersecting surfaces and measurement-uncertainty adjustments as well as large databases of terrain, obstacles, and local winds. FAA order 8260.3D contains most of the approach design structure, it is 509 pages, but even with all of that in several places it simply references the use of software, an example quote "Increase ROC values by the amount specified by the software." See 8260.3D page 198, 202-203,(cat1 final obstacle surfaces and DA) and appendix C(precipitous terrain adjustments) for some of the formulas.
This is completed with a detailed in flight inspection of the procedure using specialized aircraft to carefully map the navigation signals and controlling obstacles. The FAA also performs this service for many other countries and performs regular flight checks of existing procedures, nav-aids, and airways on a regular schedule. Some basic procedure/airway design requirements can be altered if a flight inspection determines the deviation is safe in that specific case.
As for the core components, they check obstacle clearance of the final approach segment, and recently they also compute the vertical guidance surface.(the part of final between DA and threshold. Note the 34:1 clearance symbol added to new FAA plates, it is related to VGS. Jeppeson omits this piece.) If this requires an increased glide slope angle to meet required clearances the DA may be raised for the faster category aircraft. Then the missed segment is calculated and checked for obstacles, if needed the DA is raised again so that the missed segment has required clearances. The missed segment includes an inertia allowance below DA for aircraft that fail to react until they are at DA,(this is a buffer, not intended for normal use.) this inertia is also why higher speed aircraft are given a higher DA. The difference in height between the navigation equipment in the cockpit, or antenna placement, and the wheels of the aircraft-class expected at that airport is considered for the area between DA and threshold.(A 747 will have its wheels about 30 feet lower than a cessna 172 while following the same glide path.)


The answer is: no, normal flights are not allowed under the canyon rim.

If you look at the sectional chart, you see this notice:

Searching through the CFR (Title 14, Part 91) brings up this Special Federal Aviation Regulation No. 50-2 - Special Flight Rules in the Vicinity of the Grand Canyon National Park, AZ.

Ther is also Supbart U of Part 93.

The Subpart U regulations seem to be the most current applicable regulations (please correct me if I am wrong).

The rule applies to everything under 18,000 feet MSL within an area around the park (like the chart says).

  Except in an emergency or if otherwise necessary for safety of flight, or unless otherwise authorized by the Flight Standards District Office for a purpose listed in 93.309, no person may operate an aircraft in the Special Flight Rules Area within the following flight-free zones:

It then describes the four zones: Desert View, Bright Angel, Toroweap/Shinumo, Sanup Flight-free Zone. You can't fly through these, but between them are "corridors" in which you are allowed to fly above a certain altitude. See this map for locations of the Flight-Free Zones and corridors.

There are also minimum sector altitudes for different areas, including the corridors, which are going to be the main thing preventing you from flying very low. The altitudes are different for commercial air tours versus transient and general aviation.

Also:

  no person may operate an aircraft within 500 feet of any terrain or structure located between the north and south rims of the Grand Canyon.

There are also noise limits depending on the aircraft type.

For some info on the background of these rules, see this NPS study.


Why are there no commercial supersonic flights at present?

There a several reasons for the demise of commercial supersonic aircraft.  And there is a strong possibility we may be able to take a ride on a supersonic aircraft by 2021.
Supersonic commercial aircraft have a lot of constraints on them which are not present on subsonic commercial aircraft and which military aircraft are not subject to.

Prohibitive Development Costs
Supersonic aircraft - and in particular high supersonic and hypersonic aircraft - are considerably more expensive to design and manufacture as they require the use of novel materials and manufacturing techniques in their design.  As you pass about Mach 2, heat starts to become a major problem, weakening traditional aerospace aluminum alloys to the point that they are no longer a viable material to construct an aircraft from.  The airframes also expand and contract considerably in the heat and this must be accounted for in the design.  Designers are forced to seek out more exotic materials like Titanium alloys, high temperature composites, etc.  and it is not just structure that requires novel materials to address this - fuel systems, electrical wiring, mission systems, even sealants and paint all must be chosen so as to combat heat but still satisfy traditional design metrics like safety, durability, and economics.
The result of this are very high development costs:  Adjusted for inflation, Concorde costs the governments of England and France some $28 billion or roughly 5 1/2 times the cost that Boeing spent to develop the 747.  Similar figures were consumed on the design and development of the ill fated Boeing 2707, which never progressed past the mockup stage, even after re-design.
Limited Cabin Capacities
Super Sonic Transport (or SST) design favors a slender, needle-like fuselage which limits the number of people which the jet can carry.  The Concorde was limited to approximately 100 passenger in very narrow seats; the 2707 could carry 260 people but had a length of over 300 feet making it very awkward and unruly in existing terminal aprons or taxiways.  This also makes the SST very unprofitable for its operators, as Concorde proved.  Over the last 50 years no more than 20 SSTs have ever been operational and all with only three airlines - British Airways, Air France, and the Soviet Aeroflot - all of which were heavily subsidized by their respective governments.
Propulsion Inefficiencies Restrict Range
Design of SSTs have in the past been hampered by the high fuel consumption rates of turbojet engine imposing a design range limit of approximately 4,500 NM.  This effectively curbs sales to airlines looking for SSTs to fly the pacific rim routes where the times savings offered by a supersonic aircraft would be the most pronounced.
Supersonic Flight Over Land Still Prohibited
Supersonic aircraft generate noxious sonic booms which can cause damage to fragile structures on the ground and generally are a nuisance to the inhabitants below.  While advancements in quiet supersonic transports are happening, global aeronautical regulation bodies still prohibit supersonic flight over land, restricting an SST to subsonic flight over these regions, making its operation exponentially more expensive than a traditional subsonic aircraft.
Concerns Over Safety Operating in Rarefied Atmosphere
A high speed SST would be required to operate in the higher parts of the stratosphere in excess of 60,000 feet.  While this is achievable for military pilots in full pressure suits, there are considerable risks to civilians in street clothes at these altitudes should a rapid decompression occur.  At these heights a rapid decompression will boil your blood inside your veins (very painful way to die).  It also cannot be combated with traditional supplemental oxygen systems, making such a scenario very dangerous for passengers.
Environmental Concerns
The 'dirty burning' turbojet previously discussed create a lot of NOX emissions, far more that today's high bypass turbofans, which poses risk of increased depletion of stratospheric ozone.
Cost Savings
A conventional high bypass turbofan subsonic airliner is between 16-20 times more efficient on a cost per passenger per NM basis. A typical transatlantic ticket on a 747-8 is approximately 1500 USD.  A ticket on the Concorde was about 11,000 in today's dollars.

Taken all together and faced with the reality of designing such a craft with 3 million parts, 6 million lines of software code, all tested and validated, which is restricted only to transatlantic routes, aircraft designers quickly see the handwriting on the wall and the aircraft is doomed from the drafting paper upward.
But that's not to say the supersonic dream is dead.  Aerion in Reno, NV and Airbus are in the process of developing a 16 passenger supersonic business jet, capable of Mach 1.6, with a tentative rollout and flight in 2021.  Areion claims the jet will have a 'boomless' cruise up to Mach 1.2 at or above FL350 and hopes this will coax regulating bodies into permitting supersonic flight over land.  Whether this attracts enough customers willing to pay the estimated $100 million price tag per aircraft remains to be seen.


Several reasons can be found for its early retirement:

the aircraft was instantly obsolete after one was shot down over Yugoslavia by a 30 year old SAM system
Maintenance was pretty expensive and difficult (and according to some involved large quantities of highly toxic chemicals that are still causing health problems for the people involved)
Few military reasons to keep it in the existing threat environment. An F/A-18 is cheaper to operate than an F-117 for bombing missions against insurgents and terrorists.
Politics. Retiring the F-117 could have been intended as a step towards asking for funding for more F-22s, claiming that the USAF was now without a tactical stealth aircraft for the ground attack mission (the F-22 at the time was envisioned as a multi role aircraft, having a secondary ground attack function like the F-15 and F-16).
The F-15 and F-16 have been kept in service through extensive replacement and upgrade programs for older models. There never was an upgraded F-117 proposed or built. The F/A-18 E/F are effectively a completely new aircraft and shouldn't be considered the same type as the older A/B.


Downwash is a misleading concept when discussing airfoil lift. Instead, just focus on the pressure distribution around the airfoil.

If I understand your confusion correctly, you are picturing, correctly, that there is an overall low pressure on top and an overall high pressure on the bottom, then why isn't air flowing from high pressure to low pressure?

This will indeed be the case, if there is no airflow. What you are missing is that, the static pressure distribution is caused directly by the airflow around the airfoil. The distribution is steady-state, because the combination of dynamic pressure and static pressure resists further changes; it's at an equilibrium.


What is the horizontal stabilizer failure procedure?

This would fall under catastrophic failure and theres not much that can be done. You may as well ask what will happen if a wing falls off.

but..

UA232 Sioux City. The #2 engine (in tail) blew up and took out the hydraulic lines rendering all tail control surfaces (horizontal and vertical) inoperative. The crew found they could regain limited control of the attitude of the aircraft by varying the thrust on the wing engines, increasing thrust gave some pitch up, decreasing thrust-pitch down. This was due to the line-of-thrust being below the wing. The crew did a great job of getting the airplane back to the airport and heading down the runway. Even though it cartwheeled and burned, a lot of passengers survived, thanks to the crew's action.


Was any MiG-29 modernized to incorporate digital systems?

Yes, India has designed and installed their own home-grown digital cockpit upgrades for their MIG-29's.


Why the moment arms in x-direction are considered as -x?

In your drawing, force is defined positive when upwards. By convention, pitching moment is defined positive in aircraft nose up direction. Origin of the moment is the wing leading edge, so a positive force yields a nose down moment which is negative.

Horizontal forces result in a nose up moment when above the origin, and nose down when below the origin.

That is assuming:

Positive is up, for force and position.
Positive is aft, for both force and position.
Positive is nose up, for moments.

That is the sign convention for which the equation in the book holds. The book should state the sign convention it is using, perhaps you can post that as well.


Why does the boeing 747-8 have less wing flex than the 787?

The reason is twofold: The materials used and the high aspect ratio.

The 747-8 primarily uses advance aluminum alloys, while the 787 uses carbon composites.

The carbon composites flex more compared to the aluminum alloys. This can be achieved because the carbon fibers are anisotropic and their properties can be tailored in each direction.

The yield strain of the aluminum alloys used in aerospace is ~1%, while that of the carbon composites is about 50% higher, ~1.5%.

These material characteristics mean that the carbon spar can flex more compared to the aluminum one. This effect is magnified by the high aspect ratio of the Boeing 787.

The aspect ratio of the 787 is about 11 while that of the 747-8 is about 8.5. This means that the wings are more slender and flex more for the same load.

The 787 wings are able to take this flexing in part because of the excellent fatigue properties of the Carbon composites used. See this question for a very good discussion on the causes and effects of wing flexing in 787.