May aerobatics be performed over a controlled airport without getting a waiver?

Actually "within the lateral boundaries of the surface areas of any Class D, Class C, or Class B airpace" DOES imply that you are not permitted to do aerobatics over these areas without special permits from the FAA or if there is a designated aerobatic box at that airport and said pilot remains within that airspace.  Even if you are not in the actual airspace itself, if you're above it, you're not allowed to fly acro over it.

Now, note the term "surface areas" could imply that you could fly aerobatics above or below Class C or Class B airspace SHELVES, that is a section of Class C or Class B airspace which does not touch the ground,  provided you don't enter those areas and and said airspace meets all the other requirements of FAR 91.303.

Also, some elements of the question may be interpreted in a way that would lose sight of the distinction between Class-E-to-surface areas "designated for an airport"-- i.e. actually surrounding the airport whose approaches they protect -- versus Class-E-to-surface "extensions".   Or perhaps the questioner was fully cognizant of, and following the example of, the language used in the AIM, as well as in the section headings of FAA Order 7400.11B, "Airspace Designations And Reporting Points".  In these places the phrase "Surface Area" is used ONLY to refer to Class-E-to-surface areas that surrounding the airports whose approaches they protect, and not to refer to Class-E-to-surface "extensions".  At any rate, the Class-E-to-surface "extensions" do not fall within the meaning of "Within the lateral boundaries of the surface areas of... Class E airspace designated for an airport".  One clear way to refer only to those Class-E-to-surface airspaces that actually surround the airport whose approaches they protect, is to include the phrase "designated for an airport".  For much more on the meaning of "Within the lateral boundaries of the surface area of... Class E airspace designated for an airport", please see this answer to the question "Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?", as well as this answer to the question "Does FAR 91.155c apply to class E surface extensions?"


How do airlines and airport exchange data?

Introduction : determining which gate is assigned

I assume we are talking about IFR flights with the purpose of passenger travel.

An aircraft, in order to be assigned to a gate, has to be planned and to arrive at an airport.
So let's look at the breakdown of arrival of an aircraft.

First, the airline (operator) has filled a flight plan before the flight occurred and submitted it to the legal authority managing flights in the airspace (Aeronautical Navigation Services -ANS- typically) in order to have clearance to enter the airspace, getting navigation informations and accessing the airport (more on this matter). At this moment, the airport gets informations about the next aircrafts (operator, type of aircraft, passenger, cargo etc.), which will be managed upon arrival.

Secondly, after being handled by Area Control Center (ACC) ATCO (en route flight), the aircraft is routed towards the airport by Approach controllers (APP) which manage the airplane when it flies from en route (high altitude) to the airport (ground); when the aircraft is lined up with the runway a few miles from the airport it is transfered to the tower which manages the operations from this moment (given no go around has been initiated due to runway incursion, landing mishaps etc.) and will most importantly manage ground operations (taxiing, handling take-off and landing sequences etc.).

Once the aircraft has landed and starts taxiing, the tower (TWR) will give directions to the gate it would be assigned, depending on various factors:

Negotiations with the operator : location of the aircraft at the airport has a price, aprons are more costly than parking the aircraft further from the terminal and being handled by a bus for example.
Destination and origin of the aircraft : international and regional flight can be handled in different terminals: e.g. in Europe, Schengen area flights are usually handled separately from outside the Schengen area.
Size of the aircraft : for example A380 are notable for being difficult to maneuver around airports and need specific aprons and some airport have only a few gate that can be assigned to such specific aircraft.
Available spots : the airports are incredibly busy around noon every day (look at the traffic at a major airport like Heathrow around that time), which means that some spots might be taken and the airport has to accommodate the aircraft at an available gate.

Information exchange

The tower exchange directly with the aircraft (crew or the aircraft itself) via radio or data-link, they give directions and update the gate according to the current available spots. It seems (so I might need more information with somebody more familiar with the matter) that data-link is use in most cases to share informations regarding flight details between ground and aircraft.

All in all, the airport tower decide and manages the gate. The information are stored in an operational database (at the tower or the ANS provider) and are provided to aircrafts, operators and passenger (terminals and online).

Generally speaking, the data is provided to operators via the database and a technical overlay, this can vary depending on the regions. In Europe, operators  rely on Eurocontrol Network Manager Operations Centre to exchange informations regarding flight plans, updates of flight plans and different informations regarding operations. I don't have information regarding other regions like North America.

Airport-Collaborative Decision Making

A big topic at the moment for the European airports is the principle of Airport Collaborative Decision Making (ACDM for short) which should improve the quality and reliability of these informations, by sharing information directly from the airport and the NMOC of Eurocontrol.

Though this topic is to large to cover here, it would improve such information being shared between operators, airports, aircrafts etc. and normalise the way information is shared.

Flightradar24

As for Flightradar as I pointed out in the comments, they have an explanation of how they work with data.

A final word, it seems that airport API are usually not public, and it can be expected that for examples airlines do not have other's flight information (and gate per se).


How does centre of pressure change with angle of attack?

This Wikipedia article explains that the movement of the center of pressure with changes in angle of attack depends on the airfoil shape.
In summary:

For a symmetric airfoil, as angle of attack and lift coefficient
change, the center of pressure does not move. It remains around the
quarter-chord point for angles of attack below the stalling angle of
attack.
For a conventionally cambered airfoil, the center of    pressure lies
a little behind the quarter-chord point at maximum lift coefficient (large angle of attack), but as lift coefficient reduces (angle of attack reduces) the center of pressure moves toward the rear.
For a reflex-cambered airfoil, the center of pressure lies a little ahead of the quarter-chord point at maximum lift coefficient (large angle of attack), but as lift coefficient reduces (angle of attack reduces) the center of pressure moves forward.

I do not have a simple expression that can be used to predict this movement of the center of pressure, but I suppose a computational fluid dynamics package can be used to model this for the specific airfoils used on the aircraft.


How Does the FAA Define the Dimensions of the Touchdown Zone?

Found this definition on an FAA website today:

The runway touchdown zone is usually defined as 1000 feet from the runway threshold or 1/3 the total available landing distance. This provides runway “underrun” in case the pilot comes up short of his/her aim point, as well as increased obstacle clearance while on final approach.


What frequency should be used for air-to-ground communication other than airport ground operation?

Radio frequencies in the USA are assigned by the FCC, not the FAA. There's no 'private' air-to-ground frequency mentioned in the AIM but section 4-1-11 does say that the FCC has assigned 122.900 as a MULTICOM frequency for:

  Activities of a temporary, seasonal, emergency nature or search and
  rescue, as well as, airports with no tower, FSS, or UNICOM

Arguably your fly-by is "temporary activity", however the definition of MULTICOM is:

  A mobile service not open to public correspondence used to provide
  communications essential to  conduct the activities being performed by
  or directed from private aircraft

So if your fly-by is "essential" (and safe!) then I guess you could use 122.9. There are procedures for requesting temporary air-to-ground frequencies for air shows, but that's obviously a special case.

As for legality, it seems that you need an FCC license to use an aviation handheld radio on the ground:

  You may only use your hand-held aircraft VHF radio in your aircraft
  under the terms of your aircraft license. You are required to have a
  separate Ground Station license to operate your radio on the ground.

But because this is more about FCC regulations than FAA ones, I suggest that you ask on ham.SE; they'll probably know a lot more about how it all works.


What are the most significant risks to life for the airline passenger?

Risks of dying of air travel are tiny. We can find data on direct risks of air travel, and there is an app for calculating how many years of continuous flying would lead to known aviation related chance of dying. Tiny.

Some risks ore harder to quantify though. If you fly economy class, you may be exposing yourself to the health risk of excessive sitting. It damages blood vessels and may lead to Deep Vein Thrombosis which can cause sudden death. From this news article of 23 Oct 2000:

  Emma Christoffersen, 28, died from deep vein thrombosis (DVT) believed
  to have been caused by sitting for several hours on the 12,000-mile
  flight to Heathrow from Sydney. Medical experts said she was one of
  the youngest victims of DVT, a sudden illness caused by lack of
  movement over a sustained period that claims the lives of a number of
  airline passengers each year.

Also, you're excluding the effects of airline food. An economy class meal costs between USD 2.- and 10.-, how good is that for someone to eat day in day out?

Air travel is not an activity that is good for health if undertaken on a daily basis. During a long economy class flight people should get up for a brief stroll every few hours or so, and once landed should be vigorously walking around in the sunshine over the course of a couple of days to reset their blood flow and health before taking another flight. Like pilots do.

From Mayoclinic.org:

  One study compared adults who spent less than two hours a day in front
  of the TV or other screen-based entertainment with those who logged
  more than four hours a day of recreational screen time. Those with
  greater screen time had:

  A nearly 50 percent increased risk of death from any cause
  About a 125 percent increased risk of events associated with cardiovascular disease, such as chest pain (angina) or heart attack

Air travel is very safe and mortality rates are low, as illustrated in this article from The Economist. It is a good thing though that most of us only take a couple of flights a year, with ample time in between flights. But it's not only economy class travel that is bad for health. I know people who used to be up in the air on an almost daily basis for years, flying business and first class. Unfortunately one of them is not here anymore, most probably due to DVT.


Is the transition altitude around Denali still 18 kft AMSL, and, if so, how is this handled?

The US AIP (ENR 1.7 Altimeter Setting Procedures) is pretty clear about the question being asked, and provides an example.

Minimum altitude comes first.

The lowest usable FL is raised, and not just around Denali (Mount McKinley) in Alaska where the ground juts above 18,000 feet, i.e., the lowest FL can be higher than FL 180 in the contiguous United States.

Let's say the area is not marked yellow and is therefore not congested, and no natural reserves or special conditions exist. In this case the minimum safe altitude is 500 feet AGL.

Let's say ground is 20,300 feet as you present, it means the minimum safe altitude is now 20,800 feet (based on local altimeter setting and accounting for cold temperatures). This is what the AIP says in all caps:

  1.2 EXTREME CAUTION SHOULD BE EXERCISED WHEN FLYING IN PROXIMITY TO OBSTRUCTIONS OR TERRAIN IN LOW TEMPERATURES AND PRESSURES.

Now that we've established 20,800 plus correction for temperature (assume none for the sake of explanation), the lowest FL now depends on that 20,800 plus a correction based on pressure via table ENR 1.7-2 (uploaded as image).

  2.1.3 (...) the lowest usable flight level must be the flight level equivalent of the minimum altitude plus the number of feet specified in TBL ENR 1.7-2.

(Bold emphasis mine.)

If it's a rather low-pressure day, then the correction can be upwards of 2,500 feet. Assume that for emphasis. Our total is now 23,300 feet, which makes the lowest usable FL, FL 235 (or as directed by ATC as stated in 91.159 for VFR, which the AIP mentions).

The example the AIP gives:

  The minimum safe altitude of a route is 19,000 feet MSL and the altimeter setting is reported between 29.92 and 29.42 inches of mercury. The lowest usable flight level will be 195, which is the flight level equivalent of 19,500 feet MSL (minimum altitude plus 500 feet).

This answer is based on the USA AIP at the time of writing this, it is generic, and it is not about a specific location, so do not use for flight.


Is the ILS only used for landing when weather conditions are poor?

The relevant question is not whether or not the ILS system is used at all, but when the pilot switches from ILS to visual.

At the beginning of an ILS approach, the ILS signals function as a navigation aid, helping to make sure that the aircraft is lined up correctly with the runway from a longer distance out than the runway itself would be visible clearly enough to the naked eye even in good weather.

At some point during the approach, the runway will be clearly enough in sight that the pilot can actually land the plane visually. The latest point at which this is allowed to happen is the "decision height" -- if the runway is not reliably in sight by then, a go-around must be executed.

The lower the decision height, the larger demands are placed on the accuracy and reliability of the ILS equpiment -- losing the ILS signal due to interference for a few seconds while still six miles out is much less critical than losing the signal for a few seconds right before touchdown.

It is possible (if all the involved equipment is maintained and certified to high enough standards) to have a decision height of 0 feet so the ILS/autopilot flies the aircraft all the way to touchdown, but doing this requires all other aircraft moving around on the airport surface to observe extended safety distances to the runway to minimize the risk of radio signals bouncing off their fuselages and sending a blind-landing aircraft astray. This can have bad effects for capacity, so in normal operation landings are done with a nonzero decision height.

In fact, most airports don't spend the additional maintenance cost needed to certify their ILS systems for zero decision height ("category III" ILS operation), or do it only for some of their runways. In case of bad weather at busy times, some flights will just have to divert to other airports.


What is it called when an airplane has to circle because it can't land?


Are rolling takeoffs now more common than powering up while holding on the brakes?

Whether to use a static or a rolling takeoff is usually at the discretion of the captain as long as performance is not an issue and ATC doesn't need you to wait on the runway.

Reasons to do a static takeoff include:

Less runway is required
Better obstacle clearance (mainly because of the earlier liftoff)
Takeoff engine power can be confirmed prior to brake release
ATC may require an aircraft to wait on the runway due to wake turbulence separation requirements
The aircraft manufacturer may not allow a rolling takeoff

Reasons to do a rolling takeoff:

There is sufficient runway available
Obstacles are not an issue
Takeoff engine power can be set relatively quickly and an abort can still be made at a low speed
They take less time to perform, and at busy airports this can mean getting another airplane or two out/in per hour
They offer more passenger comfort because of the smoother acceleration

Not all airplanes provide performance information for rolling take offs. In this case, a commonly used technique is to ensure that takeoff power is set by a certain point on the runway and adding that distance to your calculated takeoff roll for planning purposes.


How does one reset an attitude indicator that doesn't have a cage?

Only a mechanical inspection is likely to give you a definitive answer for why the AI tumbled, but typically it'll happen for one of two reasons: either the vacuum pump has decided to take a break, in which case the AI gyros slow down and will eventually no longer hold the instrument up, or you've exceeded the instrument's pitch and/or bank limits and caused it to tumble.

In the case of the former, there's not much you can do in a stock -172 about that. Section 3 in the PIM just tells to verify that the vacuum pump is operating with normal parameters (green arc is 4.5-5.5 in.hg). I've seen PA-28Rs with electric vacuum pumps that served as standbys to the engine-driven ones, but never seen one in a -172, not even as an STC mod. You could always try increasing the throttle; pumps in older aircraft will sometimes fail to perform as expected at lower throttle settings, but there's no guarantee there.

The latter case can happen during maneuvering flight if you exceed +/-30 degrees of pitch and 60 degrees of bank on a non-acrobatic AI. This can inadvertently happen when certain training maneuvers such as power-on or cross-controlled stalls are performed... enthusiastically. I've also seen tumbling occur during spin training. And then there was the Husky we used for banner-towing and which was pitched to 45 degrees on a regular basis during banner picks (waivers are wonderful things). The AI tumbled so regularly, the owner gave up on having mechanics reset it.

But yea, should this happen to you again, run any checklists that might exist on the topic (either directly concerned with the AI or with the vacuum pump system), and switch to partial panel ops if necessary.


Why are the AOA sensors placed outside the aircraft?

No, it is not possible to place the sensors inside the aircraft, because the angle-of attack sensors need exposure to the surrounding air, in order to measure, as you mention yourself, "relative motion between the aircraft and the surrounding air".


Why is the Tu-204 virtually immune to wing and tail icing?

Just like Teslas, being designed in California, perform worse in ice and snow than Volvos, Russian airplane designers pay more attention to icing than Western ones, where efficiency is paramount. And you can design for icing, mainly by selecting a large leading edge radius which keeps suction peaks low. In addition, large airplanes are proportionally less susceptible to icing.
From NASA:

Wings that are thin or have sharp leading edges are more efficient ice collectors. For this reason, smaller, thin airfoils may accrete more ice faster than larger, thick airfoils. A large transport aircraft will accrete proportionally less ice than a smaller aircraft traversing the same icing environment.

Also, if the leading edge radius of the wing decreases from root to tip (as it frequently does in swept or tapered wings), the ice accretion will be proportionately greater near the tip. When contaminated with ice, wings with this design may experience flow separation at the tip before the root. Note that this is exactly opposite the way clean wings are typically designed to experience flow separation. Thus, when you fly these types of aircraft, you could lose aileron effectiveness before total wing stall, increasing the probability of an uncommanded roll and greater difficulty in regaining control.

A further factor is the thrust margin of airplanes. Being a two-engined airplane, the Tu-204 has plenty of excess thrust to compensate for the addd drag of iced wings. Since icing occurs at moderate altitudes, the thrust margin there is considerable. The same is true of the B777 and the A330, of course.
But much is left to trial-and-error. Again NASA:

Some aircraft seem to be more susceptible to airframe icing than others. The reasons for this are not well understood and probably involve multiple factors. For example, there seems to be a complicated interaction between the details of the wing design (e.g., taper ratio, twist) and its relation to the fuselage.

And in Russia icing research is well established. From the website of the Central Aerohydrodynamic Institute (TsAGII)

In Central Aerohydrodynamic Institute named after Prof. N.E. Zhukovsky (part of Zhukovsky Institute National Research Centre) the considerable attention is paid to icing effect made on aerodynamics, stability and controllability of aircraft.

The T-101 windtunnel of TsAGII in Zhukovsky is specially equipped for icing studies and has been used in the design of most Russian airplanes. I could not find a confirmation but would be surprised if the Tu-204 basic design has not been extensively studied there.


Yes, they are different.  A hybrid airship has the characteristics of an airship, but it also generates lift based on its aerodynamic shape (like a powered aircraft wing).

The FAA defines an airship as having both "Lighter than Air" and "powered aircraft" characteristics.  A hybrid airship falls under the characteristics of an airship, in this sense.  However, as with any aircraft, a specific type rating may be required for a hybrid airship.

Therefore, the path to certification as a pilot of a hybrid airship will likely be very similar to, but distinct from, a typical pilot.  In particular, it may be added on as a rating to an existing pilot certificate.

https://www.faa.gov/training_testing/testing/test_standards/media/FAA-S-8081-18.pdf


How common are emergency landings for airliners? Is there really more than one per day at Heathrow?

No, there isn't more than one emergency landing at Heathrow per day

The UK Air Accident Investigation Board (AAIB) defines serious (reportable) incidents in Appendix A of this document.  If we assume that an 'emergency' landing is one caused by one of the incidents in the list, then we can examine the AAIB reports to determine the number of emergency landings at Heathrow (the site supports filters).

I could only find three incidents reported at Heathrow in 2015:

27 July 2015 Airbus A320-232, G-EUYE - In flight fumes
5 February 2015 Airbus A330-323, N273AY - Collided with airbridge
6 March 2015 Boeing 777-236, G-RAES - Air turnback due to flight crew feeling unwell

Only two of these involved an 'emergency' landing.  2015 may not be a typical year, but a cursory check of the reports for 2014 and 2016 to-date suggests that there are very few incidents.

If you want to get a feel for the number of airline incidents and accidents each day, take a look at AVHerald (you might want to make a contribution to Simon's running costs).  That site reports 29 landings at Heathrow after accidents or incidents, of varying seriousness.  You'll see that, of the thousands of flights each day, there aren't that many problems reported.


How do pilots avoid thunderstorms at night over the pacific en route to Australia where there is no radar? And what if a large front develops?

You get by on your airborne weather radar which is good out to about 80 miles.  You may also get help from other pilots ahead of you on your route providing PIREPS to ATC on HF, or talking to you directly if you are close enough to use VHF between each other.  But as far as picking your way around cells, besides being able to see them if you are in the clear, your own weather radar is all there is.

The main limitation of airborne WR is shadowing due to signal attenuation in rain, where the really nasty stuff is hidden (looks black as if the sky was empty) behind less nasty stuff.  Even with the modern radar there is a bit of skill and experience required to interpret the returns and not get fooled by shadows.


can the wreckages of a hot air balloon and a hang glider be salvaged for a working hang glider?

To expand a bit on what @ratchetfreak said in a comment...

The leading edge on that glider is not secured properly.  It would need to go around the bar all the way along the leading edge of the wing, otherwise the holes would make it so the airfoil doesn't function.

As it is right now, the air would hit those gaps and make the cloth flutter, which would break up the airflow over the glider itself.  Thus you'd just have turbulence over the wing, which would make the wing stall.

So, yeah, in a nutshell, that wouldn't work as a glider as pictured above.

But, if he had found some string or wire from the wrecked balloon and properly secured some of the Hot Air Balloon cloth to the frame...  There's no reason it shouldn't work.  Hot Air Balloons are made out of fabric that is very very similar to what hang gliders are made from.


Is there any rule in commercial aviation, that two pilots in a plane cannot be a married couple?

The Air Force, at least when I was flying there, had strict rules forbidding a husband and wife flying as crewmembers in the same aircraft.  Generally, airlines in the US don't have to have any similar policy, and there are plenty of examples of married couples (either pilot-pilot, pilot-flight attendant, or flight attendant-flight attendant) working a flight together.

An individual airline might be able to create such a policy themselves (although I have no idea if there would be legal grounds for a married couple to challenge the rule), but at least in the US there's no legal requirement that prohibits it.


Why do some Mach trimmers move the elevator?

I think it's because the 9 uses free floating elevators with servo tabs to move them.  The columns just move the servo tabs which means the actual input forces are really low and there is feel spring unit in the system.   For mach trim they just have a servo motor that applies a little pull to the column via the feel spring unit, and the rod extends to tell you the motor is pulling on the column.

There is a trimmable stab for pitch trim, but it will have a fairly primitive controller (figuring pre-microprocessor 1965 electronics) and to incorporate a mach trim mode into the stab control system was probably much more expensive than the simple setup they came up with.

The more modern setup, with hydraulic elevators that are always faired with the stab when not displaced by a control input, and a stab controller that is fully integrated into the autopilot and air data systems is way less drag.


Does an aircraft's nose landing gear extend on take off?

No, the gear doesn't actively extend, and any passive change to the strut extension during takeoff is likely to be imperceptible.

What you are perceiving during takeoff is the somatogravic illusion. It is a physiological sensation, not a physical change. Rapid acceleration, as during a takeoff roll, causes the inner ear to report what your brain assumes is your head tilting back.

The otolith organs in your inner ears sit in fluid and detect the tilt of your head. Acceleration and pitching up (or tilting back) cause the exact same movement of the otoliths. Because the otoliths are pushed backwards by the fluid, just like they would by you tilting your head back, it feels like a climb.

When an airliner is taking off, you have limited outside references to the horizon and your inner ear takes over the task of orienting you. You might notice it in smaller aircraft if you closed your eyes; in very small aircraft, the acceleration may be too slow to trigger the illusion.


What is the difference between MEL and CDL?

The MEL lists the limitations of the aircraft when some equipment (autopilot, transponder...) are inoperative.
The CDL deals only with non-structural external parts (wheel fairing...) that may be missing without grounding the aircraft.

From this website, emphasis mine:

  The CDL is a listing of regulator-approved non-structural external parts that may be missing but the airplane remains airworthy.

  To qualify an item onto the CDL, a restrictive set of conditions must be met, e.g.:

  The effect of the missing part upon adjacent structure and systems must be evaluated.
  The effect upon airplane performance must be measured.
  The combined effect upon the aircraft when more than one CDL item is present must be determined (i.e. the effect of a combination of items missing).

  [...]

  The CDL should not be confused with the MEL (MEL). While the MEL describes the limitations of aircraft operation in case of a system being inoperative/having malfunctioned (e.g. transponder failure), the CDL deals with situations where external parts of an aircraft are missing/fallen off (e.g. fairings, aerodynamic seals or panels).


Where are the fuel tank sumps on an Aquila A210?

The third drain is at the bottom of the electric fuel pump;  The AT01 is what Aquila calls the AT210 on their web site.


Will you be able to hear a supersonic aircraft flying away from you?

Yes, actually you can only hear a supersonic aircraft after it has passed over you and is now flying away from you since it is moving faster than the sound moving towards you. The sound waves will still propagate in all directions and will eventually reach you:

The frequency will be shifted according to the Doppler formula:

$$ f = \frac{c \pm v_r}{c \pm v_s} f_0 $$

Here, $v_r$ is the the speed of the receiver ($v_r = 0$ for you standing still) and $v_s$ is the speed of the sender. It is added when the sender is moving away from you. In your case of $v_s = 2c$ you would get

$$ f = \frac{c}{c + 2 c} f_0 = \frac{1}{3} f_0 $$

The audible range for a typical human is about 20Hz to 20kHz. So you would still be able to hear any $f_0$ greater than about 60Hz after the Doppler shift. The following image shows the frequencies emitted by a Boeing 747 as measured from the ground:

(W.L. Rubin, The Generation and Detection of Sound Emitted by Aircraft Wake Vortices in Ground Effect)

There are a lot of contributions from the aircraft above 60Hz, which should make it clearly audible. Of course an aircraft flying at Mach 2 will be different than a 747, but the general spectrum should not change too much.

Note: the formula above does not work while the aircraft is moving towards you because the resulting frequency would become negative. This is because sound emitted at a later time reaches you before the sound emitted at an earlier time because the aircraft has moved more towards you than the sound:


Why did the CL-400 Suntan have engines on the ends of its wings?

The Suntan project needed all fuselage space to hold three tanks for liquid hydrogen, so the engines had to be placed somewhere else. Placing them near the fuselage would put them in the range of the fuselage's shock waves. Putting them out on the wing would help with wing bending relief and ensure a clean intake flow. Once they are so far out, you can as well put them on the wingtips, so that they do not cause a pitch-up moment. On the SR-71, the engines were also placed outside the fuselage and into the wing's plane, much for the same reasons.

Keeping the intake flow uniform is paramount for the undisturbed operation of supersonic intakes, and I assume that Kelly Johnson wanted to make sure that the engines would not suffer an unstart when flying reconnaissance missions over hostile territory. With the little experience in supersonic flight in 1955 it was prudent to avoid built-in pitching moments - after all, the supersonic L/D likely was in the single digits, so an out-of-plane engine placement would had produced more moment than on subsonic aircraft.

Hydrogen was selected to achieve the highest possible flight altitude, so the aircraft would be safe from surface-to-air missiles for as long as possible. I initially thought that the wingtip location would enable to cool the hot wing structure by heating up the hydrogen on its way to the engine, but heating was planned to be done with bleed air in a special heat exchanger. Quoting www.history.NASA.gov:

  The CL-400 design divided the hydrogen tankage into three sections;
  the forward tank had a capacity of 67 000 liters; aft, 54 000; and
  center (sump), 15 000. The two main tanks were kept at 2.3 atmospheres
  pressure and the sump tank slightly lower for fuel transfer. In the
  sump was a booster pump, built by Pesco Products, that supplied liquid
  hydrogen to the engines at a pressure of 4.4 atmospheres. The engines
  were mounted at the wing tips, which meant that the liquid hydrogen
  had to pass through a hot wing with surface temperatures up to 436 K.
  The design provided a vacuum-jacketed, insulated line for this
  purpose.

Regarding the perceived danger of using hydrogen, www.history.NASA.gov says:

  Tests were devised in which tanks containing liquid hydrogen under
  pressure were ruptured. In many cases, the hydrogen quickly escaped
  without ignition. The experimenters then provided a rocket squib (a
  small powder charge) to ignite the escaping, hydrogen. The resulting
  fireball quickly dissipated because of the rapid flame speed of
  hydrogen and its low density. Containers of hydrogen and gasoline were
  placed side by side and ruptured. When the hydrogen can was ruptured
  and ignited, the flame quickly dissipated -, but when the same thing
  was done with gasoline, the gasoline and flame stayed near the
  container and did much more damage. The gasoline fire was an order of
  magnitude more severe than the hydrogen fire. The experimenters tried
  to induce hydrogen to explode, with limited success. In 61 attempts,
  only two explosions occurred and in both, they had to mix oxygen with
  the hydrogen. Their largest explosion was produced by mixing a half
  liter of liquid oxygen with a similar volume of liquid hydrogen.
  Johnson and Rich were convinced that, with proper care, liquid
  hydrogen could be handled quite safely and was a practical fuel-a
  conclusion that was amply verified by the space program in the 1960s.
  At the time, however, Johnson and Rich filmed their fire and explosion
  experiments to convince doubters.

When work on Suntan started, liquid hydrogen was a laboratory curiosity. Preparing the infrastructure needed for operating the CL-400, the Suntan project led to the building of large-scale liquid hydrogen plants. Their availability paved the way for the cryogenic rockets of the Apollo program!

Interestingly, a similar engine location was selected by the Russian design bureaus Tsybin for their NM-1 and Myasishchyev for their M-50 supersonic bomber in the mid-50s. It was started after news of the US Weapon System 110 (which later led to the XB-70) reached Russia and was similarly cancelled after two prototypes had been built and only one aircraft had flown.

M-50 during display in 1961 at Tushino airshow (picture source). Note the similarity of the Mig-21 and M-50 planform - both originated from the same work done at TsAGI.

Placing the outer engines below the wing would had caused ground contact on rotation. Speaking of rotation: The M-50 had two central gears and the bomb bay between them, and the main gear had to be placed so far aft that the M-50 could not be rotated the usual way with the elevator. So the engineers devised what they called the "galloping bicycle". When the aircraft reached 300 km/h, the forward gear rapidly extended to rotate it to 10°. Placing the outer engines B-58-like below the wing would had required an even longer gear.


What could cause a distinct tube of condensation over a wing?

What you might have seen is the condensation due to the vortex generated by the engine nacelle chine. The image below shows a vortex being generated by the chine.

Image from flickr.com. Photo credit- Frank Starmer


Which US airport historically has the most days in which VMC prevail?

According to NOAA here are the cities with >80% annual sunshine which I've used as a proxy for VMC.  You'll find these cities are all in the desert southwest region of the US where the climate is arid.

SOURCE:  http://www.ncdc.noaa.gov/oa/climate/online/ccd/pctpos.txt
DATA THROUGH 2004

CITY, STATE            ANNUAL % AVG POSSIBLE SUNSHINE        NO. OF YEARS OF DATA
YUMA, AZ               90%                                   42
REDDING, CA            88%                                   10
LAS VEGAS, NV          85%                                   47
PHOENIX, AZ            85%                                   101
TUCSON, AZ             85%                                   53
EL PASO, TX            84%                                   54

To investigate long-term trends you can access historical data at the NCDC website and analyze the data for specific weather reporting stations.


Do jet engine exhausts usually glow orange?

Both images you posted are of Pratt&Whitney J58 afterburning turbojet that was used on the Lockheed A-12 and Lockheed SR-71 aircraft. That engine ran particularly hot.

The engine was designed for operation at Mach 3.2. The efficiency of turbojet increases with speed, but only to a certain point and somewhere above Mach 2 it starts to decline. However efficiency of afterburner continues to increase, so this engine was designed to operate continuously with afterburner and to generate higher fraction of power in the afterburner than other engines.

The afterburner combustor liner was able to withstand temperature up to 1,760°C (3,800°F). The core of the flame was much hotter still, but a colder air was fed along the walls, like in all turbine engines, as explained here. The engine was also cooled by incoming fuel similarly to how rocket engines are.

Additionally, at the top speed, the compression heating as the air was slowed to subsonic speed in the inlet heated it to over 400°C (800°F) at the compressor face already. Since in the static test the air was not that hot, the engine might have actually ran a bit colder in the test than in normal operation.

This was however specific to this one engine. The compression heating is negligible at subsonic speeds and grows faster at higher Mach numbers. Most supersonic aircraft fly around Mach 2, where the effect is already noticeable, but not nearly as pronounced. For most engines, they run at roughly the same temperature in test as they do in normal operation. It just isn't as high as in this special case.


Does rolling affect the thrust of a propeller?

for a propeller rotating at 2400RPM = 40 rev/second and a roll rate of 0.3 rev/second, the roll rate will not measurably affect the prop rotation speed and the plane will neither travel faster (if the rates are additive) nor slower (if the rates are opposite).


Why is radar required on some FAA instrument approaches?

Radar is most likely required in this case because there is no defined Initial Approach Fix (IAF).

Also note that in the profile view TIVNE and HORVI have the word RADAR underneath, which means that if you wanted to fly to either of those way points, including a course reversal in the hold, you would still need to be vectored by ATC via RADAR.

This means that ATC needs to give vectors to final or otherwise provide a specific clearance to establish an IFR aircraft on the approach.

There may be other considerations, but that is the main one that I see here.


Looking at this FAA notice from the 2012 RNC convention in Florida, there are multiple references to "gateway operations" and "gateway airport(s)". Specifically:

  Aircraft not operating under a TSA-approved standard security program ... when the TFR is in effect must be security screened by TSA at a designated gateway airport or location.
  ...
  TSA security screening and gateway operations will be available on August 26 for those operators wishing to operate into St. Petersburg-Clearwater International Airport.
  ...
  TSA security screening at the gateway locations will consist of ID
  verification of all passengers and crew, watchlist matching, physical screening of persons and baggage, and inspection of the aircraft.
  ...
  Positive pilot identification procedures will be in effect during this TFR. Special ATC procedures and routes to and from this airport may be assigned prior to departure from a gateway airport. Upon departing the gateway airport, all aircraft must be on a VFR or IFR flight plan, maintain radio contact with ATC and continuously squawk an ATC-assigned discrete transponder code. Intermediate stops are not authorized unless there is an emergency. If an intermediate stop occurs, aircraft will be required to return to a gateway airport to be re-screened prior to continuing flight with the TFR

Then referencing this TSA post:

  Dulles International Airport (IAD) will serve as the newest gateway airport, allowing certain pre-cleared general aviation operations, including corporate aircraft, charter flights, and on-demand operations, to fly directly into Ronald Reagan Washington National Airport (DCA).
  ...
  Aircraft must arrive from one of 17 gateway airports after flight crews have been vetted and passengers screened.

So it would appear that "Gateway operations" are specific security protocols for departing and arriving aircraft within a certain restricted area.

EDIT:

It appears that, if "Gateway Airports" and "Gateway Operations" are synonymous, that it is about strict preclearance procedures defined post 9/11. As far as I can tell, these restrictions are permanently in place for flights in Ronald Reagan National Airport (DCA), due to the obvious risk the airport's proximity poses to various Federal government buildings.

These rules are called "DASSP" for DCA Access Standard Security Program. The consist of the following regulations

  TSA inspection of crew and passengers.
      TSA inspection of property (accessible and checked) and aircraft.
      The start and end dates of flight must be indicated on the TSA flight authorization.
      Identification checks of passengers by TSA.
      Submission of passenger and crew manifests 24 hours in advance of flight.
      Enhanced background checks for all passengers and fingerprint based criminal history records check (CHRC) for flight crew.
      Armed Security Officer (ASO) on board each flight.
      All operations are subject to cancellation at any time.
      All unscheduled operations to/from DCA require an FAA Slot Reservation.


How should the pressure coefficient distribution from a wind tunnel experiment be interpreted?

First, your pressure values cannot be the measured pressure, because they are negative. This indicates that they are pressure differences.

Next, their magnitude is too low to be in Kilopascal. Could it be that you list already the pressure coefficient?

Third, when plotting the pressure coefficient, it is customary to invert the Y axis, so the most negative value is on top. This just makes the plot look more familiar.

If I do this with the tabulated values, this is what I get:

Plot of tabulated values (own work). I extended the Y axis down to +1 on purpose, because this is the stagnation pressure coefficient in in compressible flow. Your data looks like that of a very thin symmetrical airfoil at an angle of attack near 0°.

Now look at this computed plot of pressure coefficients of symmetrical airfoils at zero angle of attack (source):

Inviscid pressure distribution of symmetrical NACA airfoils. The black line looks like your data. Unfortunately you never mentioned which airfoil the measurement is from, but to me it looks awfully like a NACA 0006 (or even something thinner).


What could cause an inadvertent squawking of 7700?

A transponder in most planes look something like this

(source)

The code is changed by turning the knobs beneath the numbers. Lets say you are assigned 5700 as your code but your previous code was 7456. If you are careless or start from the right most knob your transponder will briefly be set in 7700 until the most significant digit is changed. If the radar does a pass (interrogation) at that time ATC will momentarily receive a 7700. Some people say you should put your transponder in standby (SBY) mode when changing codes to avoid this happening.

Some GA planes (and even some larger planes) have newer digital interface transponders like this one,

(source)

These make it a bit harder to pass through the codes since you are not turning knobs but in bumpy air you could accidentally double tap a number. For example lets say you are assigned 7003 in bumpy air. You go to hit the 7 and accidentally double tap the button. Then you type in the 00 and your code is complete by the time you hit the 3.

After some looking it seems that larger aircraft user a transponder like this one,

(source)

In this case you will see a similar case to the first transponder listed. If its not in STBY while switching you inevitable have to pass over 7700, 7600 or 7500 to get to some codes. If an interrogation happens at that time it may cause the results you mention.

In terms of switching to STBY mode, the only documentation I can find about keeping the transponder in altitude reporting mode is this document which states

  operators and pilots of the need to ensure that transponders are in the
  altitude reporting mode whenever their aircraft is on an airport movement area at all airports.

This was issued in May of 2015 and seems to be related to the ground surveillance systems being installed at airports.

The FAA FAR touches on transponder operation in S91.215 and part C reads

  (c) Transponder-on operation. While in the airspace as specified in paragraph (b) of this section or in all controlled airspace, each person operating an aircraft equipped with an operable ATC transponder maintained in accordance with Sec. 91.413 of this part shall operate the transponder, including Mode C equipment if installed, and shall reply on the appropriate code or as assigned by ATC.

This section simply states that you must "operate" the transponder on the code assigned while in required airspace. That seems a little vague and does not completely exclude putting it in STBY mode to switch codes.


Why does the F-16 have a fixed stabilizer section inboard of the stabilators?

The F-16 has an all moving tail plane all right. What you are referring to as the 'fixed part' is actually the fuselage portion which houses the air brakes. It can be seen clearly in the following photograph.

Belgian AF stabilizer; image from designer.home.xs4all.nl


How many kilowatts to get an electric 747-8 airborne?

First, let's figure out how much power a 747 needs to takeoff:

Assume:

Engine thrust = 284 kN
Takeoff speed = 170 knots
Takeoff power = 90% max power

Using $P=Fv$, converting the variables to SI units, we get
$$Power=88,948,800 W$$

Or, in other words, around $90MW$.

EDIT: This calculation is only correct if the engine efficiency is 100%, because it is based on work done. For a realistic estimation, see Jan Hudec's answer. I'll leave the rest of this answer based on 90MW as I'm too lazy to update the numbers.

But just exactly how much is 90 megawatts?

An average laptop computer consumes 20W on daily use. You can power 4.44 million laptops with this power.

A high-end desktop consumes 300W under heavy load. You can power 300,000 desktop computers. If you stack 20 of them in a server tower and put 100 towers on each floor, you need a data center with 150 floors to fit those machines in.

Let us take this a step further and evaluate the total energy needed for a flight. Assume all required energy comes from onboard energy storage (i.e. no solar panels / windmills). Let's also assume a full power climb to cruise altitude of 15 minutes, 50% power cruise for 4 hours, and a completely idle descent which does not consume any power at all.

Using $E=\int P dt$, we get the total energy needed for a flight is $$720,485,280,000 J$$

With that amount of energy, you can pull a 735 kiloton object up 100m. If all those weights are water, that's close to 300 Olympic swimming pools.

If you power the whole plane with batteries, you'd need 47 million AA batteries.

Of course, if you manage to get 14 of these electrical 747s together, you can generate 1.21 gigawatts and get Back to the Future.


Why aren’t multiengine general-aviation aircraft required to be capable of sustained single-engine flight?

It is legal to operate a light twin with anemic or nonexistent
single-engine climb performance.

No, and technically it would not be certifiable as airworthy as per § 23.67 Climb: One engine inoperative. Aircraft that were certified at a different point in history may subscribe to different regulations.

(a) For normal, utility, and acrobatic category reciprocating engine-powered airplanes of 6,000 pounds or less maximum weight, the following apply:
(1) Except for those airplanes that meet the requirements prescribed in § 23.562(d), each airplane with a VSO of more than 61 knots must be able to maintain a steady climb gradient of at least 1.5 percent at a pressure altitude of 5,000 feet with the -
(i) Critical engine inoperative and its propeller in the minimum drag position;
(ii) Remaining engine(s) at not more than maximum continuous power;
(iii) Landing gear retracted;
(iv) Wing flaps retracted; and
(v) Climb speed not less than 1.2 VS1.

In other words if you can get to ~5000 Ft. you need to be able to maintain a nominal climb in a light twin.
The regulation for aircraft over 6000 lbs. is similar as well depending on where you draw the line for "light". There is also more information on how the testing occurs in this AC.


Are there any EU/EASA regulations surrounding aviation software?

If we speak about airborne software, the main document is the RTCA/EUROCAE DO-178/ED-12 currently at the "C" version: Software Considerations in Airborne Systems and Equipment Certification: if you want to certify (and thus commercialize) your software for flight, this is the main document to read.

Depending on the scope of the software and the design/development process there might be different supplements (see here):

  DO-330 Software Tool Qualification Considerations
  DO-331 Model-Based Development and Verification Supplement to DO-178C and DO-278
  DO-332 Object-Oriented Technology and Related Techniques Supplement to DO-178C and DO-278A
  DO-333 Formal Methods Supplement to DO-178C and DO-278A

It has been prepared by the RTCA/EUROCAE joint committee and approved by both FAA and EASA under different names, but the content is the same.

As @Greg mentions, these documents are not freely available


Is there really anything to be gained by placing the propeller at the top of the vertical stabiliser?

To place a heavy mass, part of which is even rotating, on a long, flexible beam is generally not a good idea. The engine mass will reduce the eigenfrequency of the vertical tail, inviting early flutter, and any imbalance in the propeller will provide the initial excitation which flutter needs to develop. Also, placing heavy masses away from the center of gravity increases the moments of inertia and makes the handling of the aircraft needlessly sluggish. The designers must feel some pain to pick this unattractive engine position.

Reasons for this unusual engine placement could be:

Better aerodynamic control for ground handling. With the control surfaces squat in the propeller's slipstream, ground handling of seaplanes on water is much improved.
Better visibility for the pilot: Instead of a center engine placement in the nose, a tail location gives much improved visibility.
Less FOD (foreign object damage): The raised prop position makes it less susceptible to being damaged by debris kicked up from the ground.

The first reason explains why most designs with tail-mounted engines are seaplanes. The engine location on the Trislander, the three-engined version of the Britten-Norman Islander, was picked for the last two reasons and because the designers felt that flutter was not much of an issue with that compact, slow utility aircraft.


What is the advantage of combining the rudder and brake pedals in aircraft?

All of the aircraft that I have ever seen have the rudder and braking functions combined into one set of two pedals.  To operate the rudder you press on the bottom part of the pedals, so that they slide back and forth on tracks, and to operate the brakes, you press the top part of the pedals so that they rotate towards the floor.  The left pedal operates the left wheel brake, and the right pedal operates the right brake, so you can use differential braking to turn the plane.  For rudder operation, the motion of the two pedals is locked together (i.e. press on the right pedal for right rudder, and the left pedal moves aft while the right pedal moves forward).

Because of the two different motions (rotation for brakes versus sliding for rudder) there isn't a problem with hitting the brakes when you want rudder or vice versa.  Typical early training is to operate the rudder using your toes on the lower parts of the pedals, so and to only put your whole foot on the pedal to actuate the braking mechanism.


How did this flydubai 737NG get Max winglets?

These are called Split Scimitar Winglets and they are offered as an upgrade for some existing Boeing 737 NG series aircraft:

Split Scimitar Winglets are offered by APB for the 737-800 and 737-900ER and came into service in early 2014. They are available as a retrofit to existing winglet aircraft.
A set of SSWs weigh 133kg (294Lb) per aircraft but give fuel savings of 1.6% on sectors of 1000nm rising to 2.2% on sectors of 3000nm. This equates to an extra 65nm range.
The modification requires a trailing edge wedge, strengthened stringers and ballast weight but no changes to any avionics or the FMC. The base price cost for an upgrade from blended winglets to SSWs was $555,000 as of 2014.

(b737.org.uk)
According to this article (in German), Flydubai is using this upgrade since 2019:

The low-cost airline from Dubai is equipping 30 Boeing 737-800s with so-called Split Scimitar Winglets. The scimitars on the wing tips save thousands of liters of fuel.
[...]
The first aircraft of the low-cost airline from Dubai - it bears the A6-FEC registration - has already been equipped with the split wing tips.

(translated by Google)
It is not exactly the same winglet as the MAX has (see also Why do newer 737s use two different styles of split winglets?) as you can see in the following images:

(Flydubai Boeing 737 NG, aerotelegraph.com)

(Flydubai Boeing 737 MAX, photo by Nabeel A. Hashmi)


Was flying a helicopter below building height against FAA regulations?

I don’t know exactly where in DC that happened, though I would say it’s highly probable that it was a public or law enforcement helicopter, or a lifeflite helo as virtually nothing else is allowed to fly VFR in the FRZ over DC without a lot of planning and waivers.

Helicopters, under general operation, are going to have to conform with §91.119(a), (d)(1), which state you must operate the helicopter at an altitude that, if a power unit were to fail, a landing can be made without creating an undue hazard to persons or property on the surface.  In the case of the helo in question, it’s a Eurocopter EC 135, which is a multi engine aircraft.  I don’t have the performance charts for that helo handy, but I believe it either can hover OGE or perform and aurtorotation landing at near standstill should an engine fail.

There’s also the fact that, as many cities right now are under a state of emergency, public vehicles may be forgoing a lot of regulations on flight ops for that reason.  The helo may also be looking for a place to land and hoping the people below can make a space for it.  I’m not sure here.


How are the BNR and BCD data formats identified in an ARINC-429 message?

The receiver has to be programmed.  It's important to remember that A429 is a unidirectional hard-wired bus with a single transmitter and multiple receivers.  Each connection is physically unique and the reason for all the pin-out diagrams and bus definitions in the ARINC Characteristics.

To help with data integrity and fault detection, each transmitter includes Label 377 on the bus which contains its equipment ID.  For each type of equipment, the label assignments and coding are fixed.

So, if you're building an LRU that's receiving GPS data, you would program the port assigned as the GPS#1 Input to verify the equipment code is 00B hex and the find the specific labels your LRU needs (it's likely to be a small subset of all data on the bus).  Since you know the source LRU and the Labels you're looking for, you know the individual label coding and can program the receiver to decode the data.

Most avionics companies have developed custom ASICs to act as the A429 UART.  It simplifies the design and saves costs.


How do aircraft differentiate between missile locks?

Non-holographic radar systems such as those used in fighter aircraft and active guided missiles only point in one direction at a time. Normally, when the radar is in search mode, a mechanism inside the radar makes the beam move from side to side (possibly up and down as well), so it has a wider field of view and can pinpoint the direction of any aircraft it finds.

The aircraft with the radar warning receiver (RWR) sees a brief pulse of radiation every second or so: only when the beam is pointing in its direction. This way, it knows the radar emitter is in search mode, and the direction of the emitter. Every aircraft in the radar's field of view will see the beam at different times, and they will all see the radar on their RWR screens. In a combat zone this is potentially a lot of emitters, but the RWR can analyse the radar signal to identify the radar: what type of aircraft, SAM, or ground radar it is, and whether it's friendly or enemy.

Getting the position of the target only every second isn't good enough to guide a missile towards it. When the radar is in track or launch mode, it stops scanning the beam, and keeps it pointed at the target aircraft.

The RWR on the target aircraft now sees much faster pulses of radiation, so it knows that it is the sole target of the radar. At this time, it can warn the pilot of a missile lock. But because the radar is now only pointing in this one direction, other aircraft in the area don't get illuminated by radar at all. Their RWR systems won't pick anything up. Only the aircraft that's actually threatened gets the missile lock warning.

In addition, the same analysis that can identify what type of radar is illuminating the aircraft can also identify fully active radar-guided missiles. Like when the aircraft's radar is in track or launch mode, the missile's radar emitter only points in one direction, and doesn't scan, so only the target aircraft will see it.

Obviously it's a little bit more complicated than this. There are a lot of details about how frequent the radar pulses are, and how the RWR knows the range of the source, but I hope I've captured all the important information in an understandable way.


Are there standard visual cues or other methods for flaring in a B737-800?

I'm not sure I understand what you're asking, but proceeding from what I think you may be asking, consider the following.

Are you flaring from a stabilized approach? Until a pilot internalizes things for any large aircraft, using a stabilized approach on speed appropriate to your landing weight gives a common, starting reference to work from.

From such an approach you should have been given in training the altitude from which to start the flare. For purposes of discussion, let's say that's the 50 feet you mentioned. Thus, the first problem is determining when you're at that point. Assuming you have a radar altimeter, are you using the call outs from the altimeter to consistently start the flare at the same altitude?

Now, in a stabilized approach, you don't feel a change in sink rate in the seat of your pants until you actually start the flare, so when you say "the sink feels too much", I'm assuming that you're having trouble with the rate of your flare. In other words, how much back pressure you should be exerting on the yoke. My thought would be that you could try focusing on how much to raise the nose at the 50 foot call rather than trying for a given amount of feel in the seat of your pants. I never flew the 737, but on the 747, at the 50 foot call, I would would raise the nose to 5° higher than it was during the stabilized approach. Then at the 10 foot call, I would raise it 2° higher yet. There would, of course, be an appropriate power reduction each time.

The 737 will have different numbers than the 747, but what I'm suggesting is to try doing it by the numbers, consistently, every time. Any 737 instructor should be able to tell you what those numbers are. You might even try posting a question here asking specifically what those numbers are. Perhaps a 737 pilot will see this answer and provide them.

Finally, an advantage of doing things by the numbers is that it really doesn't matter what your seat position is, although you should certainly go for a seat position that will eventually allow you to best internalize what the numbers mean insofar as the view out the windshield. When I transitioned from the F-27 to the SA-227, I found the view out the front confusing, but no matter since they taught us to simply do it by the numbers at first.

My apologies if my answer has been too pedantic or if I have misunderstood the question. If so, let me know in a comment and I'll be happy to delete the answer.


Do pilots get more fresh air than passengers?

Taking the B737 as an example, fresh air from the left pack flows directly into the cockpit (green airflow in the diagram), whereas the passenger cabin is served from the mix manifold only (yellow). Therefore

pilots receive 100% fresh air
while passengers receive a mix of 50% fresh air and 50% re-circulated cabin air on average, across all aircraft types

share of re-circulated air (red) in the cabin ventilation air (yellow):

B737: pilots 0% passengers 25%
B757: pilots 0% passengers 50%
B767: pilots 0% passengers 50%
B777: pilots 0% passengers  ?

In a cabin packed with hundreds of people each transforming 21% O2 and 0.04% CO2 into 16% O2 and 4% CO2 (i.e. breathing) and where 50% of this exhaled used air (red) is recirculated back into the cabin (yellow), O2 and CO2 levels are poorer than in the cockpit not supplied with exhaled used air.

The AFA-CWA flight attendants association indicates how much fresh air each person receives:

  How much air is supplied in the economy section? 6-10 ft³/min of outside air to each person which is about half what is recommended in
  buildings and transportation vehicles.
  The cockpit gets 50-100 ft³/min per person of outside air, or sometimes a mix of outside and recirculated air depending on the
  aircraft type. That is up to 20 times more than in the passenger
  cabin.


At what rpm does the tip of a 54" propeller start to incur mach losses?

A 54 inch propeller would start to incur efficiency loss at approximately 4300 rpm.

At 4300 rpm a 54 inch propeller would have a tip speed of 691 mph which, relative to the 767 mph speed of sound, is about the maximum which still allows propeller efficiency.

You can calculate the variables using this tool: WarpDriveProps.com Propeller Tip Speed Calculator


What is the reason for not providing glide slope guidance on the western approach to Innsbruck?

Looking at the charts, I can see quite a few good reasons for not providing glideslope for the West approach:

The East approach leads you (almost) directly to the runway threshold, the West approach leads you a few miles east of the airport.
The East approach has more terrain clearance. If you go only slightly below the glideslope for the West approach, you will be dangerously close to terrain.
The descent profile is steeper for the West approach: you are expected to lose 1500 feet for every 3 miles you travel. For the East approach it's 1320 feet for every 3 miles.

Number 1 is very important. If some pilot decides to blindly follow the ILS needle on a East approach, eventually he'll see the runway. If a pilot does the same on a West approach, eventually he'll crash his plane somewhere in the valley. The absence of glideslope reminds the pilot he has to pay attention to the vertical space.

Tracking the glideslope accurately is also pointless, as the pilot will transition to a visual approach and circle around anyway. It won't make big difference if you were a little bit off the initial descent.

For reference, East approach:

West approach:


Under what conditions are passengers required to take precautionary measures during refueling?

Doc 965, CAT.OP.MPA.195(b), regarding Refuelling/defuelling with passengers embarking, on board or disembarking, says:

  For all other types of fuel, necessary precautions shall be taken and the aircraft shall be properly manned by qualified personnel ready to initiate and direct an evacuation of the aircraft by the most practical and expeditious means
  available.

So no-belts restriction is one of the elements that ensures "expeditious evacuation". The same goes for keeping the doors open and keeping the passengers in their seats.

Although the legal requirement is not that specific, probably the detailed procedure (with all the elements you described and others that were not visible for the passengers) can be found in the company Operations' Manual.


Where can I find detailed dimensions of an aircraft engine compressor blade?

Since nobody's answered this yet, I'll take a stab at it.
I tried to find some dimensions for you online, but struggled.
Here's a thought though, could you just buy one?
For example - £35:

This is a Rolls Royce Olympus 593 Turbojet engine High Pressure Compressor Vane. This is a flown item that powered BAs Concorde fleet and the blade shows signs of use.
It was manufactured by Rolls Royce and has the Olympus 593 part number B430542.
The dimensions of this item in centimetres are approximately 15.5 x 4 x 4 and it weighs approximately 400g.

There are lots more on eBay too.
You asked about material — one listing says the Tornado's Rolls Royce RB199 engine is made from titanium.


Can an ultralight aircraft fly with a 18hp engine?

It's possible to arrive at a rough estimate by assuming that the L/D ratio is 9. Now, the empty mass is 70 kg. Let's add 45 kg for the engine, transmission and propeller. And we must not forget the mass of the pilot (85 kg) and 20 kg of fuel. It's a total mass of 220 kg. Let's round it to 250 kg in order to be on the safe side.

If we imagine the plane gliding at L/D = 9 and 25 m/s, the sink speed will be 25/9 = 2,78 m/s. As the mass of the plane is 250 kg, its weight is 2450 N. Thus, the 'gravitational power' involved in the glide is 2,78 x 2450 = 6805 W.

The plane, for straight and level flight, will need exactly that power. If we assume that the transmission and propeller losses are 50%, you'd need twice that power, that is, 13,6 kW. Besides, some extra power is needed, (in order to climb, for example...) so let's increase the figure by 30%. 13,6 x 1,3 = 17,68 kW = 24 hp. That's the engine power that, in theory, and according to this simplified estimation, would be needed for that plane...


How does new media streaming technology equate to fuel cost increase?

Because it says "drag", my guess is that implies an external antenna.
For example (which I found using a Google search),

Commercial and Large VIP Aircraft Broadband Internet Solutions
HR6400 Antenna System
The HR6400 antenna system for commercial and large VIP aircraft
provides passengers and crew true wireless broadband Internet access.
No matter where you fly - over land or water in any region of the
world - you can browse the Internet, send and receive emails in
real-time, use Voice-Over-IP (VoIP) telephony, access your VPN,
conduct video conferencing, and watch IP television.
The emerging standard for Ku-band systems with the most efficient
Ku-band antenna available, the HR6400 is mounted on the aircraft's
fuselage, providing all the performance you need in the smallest
possible footprint. The easy-to-install HR6400 comes complete with
antenna, antenna control unit, high power transceiver, radome, and
radome attachment ring. It covers everything from the energy coming
from the satellite to the modem connection.

For example, here is a typical antenna installation (not necessarily the one mentioned above) on a 737:


How is an air accident's probable cause determined?

I participated in a tiny supporting role in a few crash investigations involving CRJs, so I'll give it a shot, and I would say that when a main cause is listed, especially for something mechanical, it's what you might call a "primary trigger", without which, follow-on supporting factors  and events that led to the crash would never have occurred.  Or an event in a chain that can be considered the "point of no return".

Pilot with poor training takes off in an overloaded airplane, and engine quits after V1/VR and it crashes.  The engine failure will be the main cause, with poor training and overloading added as contributing factors.  Without the engine failure, the poorly trained pilot in his overloaded airplane would've carried on his merry way, so the engine failure can be considered the main cause.

For pure "pilot error" events, it can be more nuanced, with a roughly equal-in-impact chain of events and if you took out any element in the chain, the other elements may have still happened, but just not leading to a fatality.  These reports will often list a series of accident causes without giving critical weight to any one, except to say that the cause was ultimately the crew and not the plane.  Running out of gas is a typical one.

On the other hand, sometimes a crew action is as much a triggering event as a major mechanical failure.  Colgan Flight 3407 is a classic example of this.  The Capt had the Mother of All Brain Farts and pulled when he should have pushed when the shaker went off and this is listed at the main cause.  Now, the shaker went off in the first place because they weren't paying attention to power when the A/P leveled off, but it was the response to the shaker that sealed their fate, and becomes the main cause.

There was a CRJ crash in China caused by taking off with frost on the wings on a cold clear morning.  Frost on the wings was the main cause.  Lack of understanding of the effects of frost, and maybe a bit of normally benign over-rotation-on-takeoff contributed, but without the frost, nothing would have happened.


How can I calculate the fuel consumption of an Airbus 320-200 at various loads?

If you need precise values, you need to provide much more detail. Fuel consumption is affected by many parameters; see this answer for more detail.

For a precise estimate it will be best to employ a simulation software; see the answers to this question for more detail.

If you are just interested in a general estimate, the venerable Breguet equation will already give good results. First we need to know how much difference the 20% in load factor makes: The average mass of a passenger plus baggage for short-range trips is 100 kg, so the zero-fuel mass would be OEW + 18 t = 60.6 t in the 100% case and 3.6 tons less in the 80% case. Allow for 3 t of fuel reserves and plug that into the Breguet equation, using a fuel burn of $b_f$ = 0.000018 kg/Ns and a speed of Mach 0.78, which equates to $v$ = 262 m/s in 11.000 m altitude:
$$m_1 = m_2 \cdot e^{\frac{R\cdot g\cdot b_f}{v\cdot L/D}}$$
The L/D should be 18 and for the range we use R = 2000.000 m. $m_1$ is take-off mass and $m_2$ landing mass. This gives $m_1$ = 68.54 t for the 100% case and $m_1$ = 64.66 t for the 80% case. To be realistic, you would need to include different fuel flow during climb and descent, but the real value shouldn't be too far from the 5 rsp. 4.7 tons we get from the Breguet equation.

Note that when you repeat the calculation for 5,700 km range, the take-off mass comes out at 78.7 t for the 100% load factor, which is almost exactly the MTOW of the A-320. With 2.3 t of reserves, the Breguet equation gives you exactly the specified performance of the A-320-200. This should give you some confidence in those results.


Can an airliner provide ground level cabin pressure, temperature, humidity etc?

I'll touch on the humidity a bit.

This is actually a big issue for planes; they tried to make it a bit better on the Dreamliner and were able to bump it up a bit

  Humidity is improved, yet still dry as the desert. Humidity levels on the Dreamliner are 10%-15% — better than 7% on other planes on long trips

source

but it's still a big issue. There are two main reasons they can't really increase it that much.

First off, water is very heavy. Since planes pump in dry exterior air they would have to humidify it which means they need to carry enough water to do so. This weight would greatly affect the useful load of the plane. Now you could try to recycle some of the ambient moisture, but on a large scale that takes power, which takes fuel, which comes back to the weight issue.

The other issue (although not as often thought about) is the longevity of the airframe. The extremely dry conditions that airliners see for most of their time actually helps to prevent corrosion on the airframe as well as rust on any rustable parts. By pumping moisture into the airframe you will run the risk of it causing real damage to the metal components.

The temperature is a simple energy problem. To keep a plane hot you need to heat it faster than the exterior temp is cooling it (or evenly to keep it a constant temp). Insulation can help with this but you are still going to see some cooling. On a rudimentary level you can apply Newton's law of cooling here and keep in mind the exterior temperature is in the -40 (and below) area (according to today's charts).

On to the pressure,

This, of course, is a big one, but, in reality, it's not a big deal. While it may seem a bit irritating, 8000ft atmosphere equivalent is still more than breathable. The FAA does not require continuous O2 until 14,000 ft for unpressurized planes, so an 8000 ft equivalent cabin is more than fine. Now from a comfort standpoint, your ears may pop and you may feel some discomfort, but it's more than safe.

From a purely technological standpoint we can do this, but from an engineering use case standpoint it's better to sacrifice some of the pressure to build a lighter, thinner plane. This saves on fuel and material costs down the line. There is great hope that carbon fiber may bring a change to all this and 8000 ft equivalency will be a thing of the past. Boeing has been pushing this with the 787 having only a 6000ft pressure level which they claim alleviates problems. I have not yet flown one so I don't know first hand how much better it really is. Then again I fly unpressurized stuff often and have become somewhat acclimated to it.


What's the difference between Holding Point and Hold Short?

The U.S. and holding point
It depends on the locale and context. For taxiing in the US holding point is not used as the FAA ATC manual refers to it as an ICAO term for a visual (or otherwise) holding point in the sky.

HOLDING POINT [ICAO]− A specified location,
identified by visual or other means, in the vicinity of
which the position of an aircraft in flight is
maintained in accordance with air traffic control
clearances.

Elsewhere and hold short
Elsewhere for taxiing, holding point is where the intended departure will take place from a runway. Check eurocontrol.int for examples (direct linking not available), but here's an example they give:

TAXI TO HOLDING POINT [number] [RUNWAY (number)] VIA (specific route to be followed), [HOLD SHORT OF RUNWAY (number)] or [CROSS RUNWAY (number)]. [REPORT VACATED]

Taxi to holding point A, runway 36, via A.

That means take A all the way to the end where it meets runway 36 and stop at the hold short line or behind whoever is ahead.

Taxi to holding point C, runway 36, via A and C.

Here the runway was shortened (an intersection departure) and the pilot will hold at C and then line up from C when cleared.
Report holding point means report when you get there.

Tower, Stack 1 is at holding point A, fully ready.

Hold short is the same everywhere and applies to any intersection or runway on the way to the runway/gate.

Taxi to holding point A, runway 36, via A, hold short C.

Here the pilot will hold where C meets A and awaits clearance to continue.

Hold your position is an instruction to stop right now.
Some airports employ LAHSO (Land and Hold Short Operations), where a hold short line exists on the runway you are landing on.

Example: Cleared to land runway 27, hold short runway 22L.

Example in Boston Logan (blue circle):


How can I calculate the speed gain from using multiple STC modifications together?

Not practically speaking no.  With sufficient engineering data you could perform calculations to come up with a model for what the additive effects would be of the various modifications.

The problem with the aerodynamics to horsepower relationship is that almost all of the basic calculations have exponents.  So a mod that gives you 5 knots over a given 'stock' airspeed will not give you close to the same number at a different higher base airspeed.  So with three 5kt estimated improvements you end up with maybe 5 knots for first mod, 3kt for 2nd, and perhaps 1tk for the 3rd.  Add to that the complexity of really subtle interactions in aerodynamics could mean that one mod may make the other 2 yield no differences in cruise.

Take for example a TBM850 which cruises 300mph on maybe 800hp vs a Cessna 210 at under 200 mph on 300hp vs a piper cub going 100mph on 75hp.

Not apples to apples, but to give a sense of the scale these effects have.


Are there any aircraft used in part 121 (aka scheduled airline) operations that do not require a type rating to fly?

Cape air has a fleet of 83 Cessna 402s, some of which are involved in its Part 121 operation.


The CVR (and FDR) are continuously recording while the aircraft is in operation. In the days of magnetic tape, this was done with a continuous loop. In digital systems, the same is emulated by automatically returning to the start of the storage area whenever the end is reached. In both cases, the new data always overwrites the oldest data, so the last N hours is always available. When there is a crash, investigators locate where along the loop the accident occurred, and then read all the way around the loop (physical or virtual) until they reach the accident again.


The code is for the exact variant for this Airbus:

A321: This is an Airbus A321, the longest variant of the A320 family.

27*: It comes with PW1100 engines (which makes it a neo).

271: The exact engine variant, which can be found in the TCDS (Type Certificate Data Sheet):

PW1133G-JM Geared Turbo Fan jet engines (MOD 161002)

N: Added for all neo variants.

X: This means the aircraft has Cabin Flex, which allows the operator more freedom in choosing emergency exits:

these doors’ configuration flexibility are there to enable all customers’ operational needs without compromising on cabin comfort

(runwaygirlnetwork.com)

The "Cat D" you mentioned is the approach speed categorisation:

Category
Approach Speed

A
< 91 kt

B
91-120 kt

C
121-140 kt

D
141-165 kt

E
166-210 kt

The Airbus A321 can be in approach category C or D, depending on the maximum landing weight:

A321 has Approach Category C to 75.5 tonnes MLW and D beyond that to 77.8 tonnes.

(SKYbrary - Airbus A321)
You can find the maximum landing weights for the A321neo in the Airbus Aircraft Characteristics Document:

All maximum landing weights for the A321neo are above 75.5t, which would make them all Cat D.


Which portion of combustion energy is used to spin the compressor of a pure jet engine?

The accelerated air coming out has more energy than the air ahead of the engine, even at idle-power.

Force and mass flow rate:
In constant speed level flight, the forward thrust acting on the jet engine(s) equals all the drag forces acting rearward on the airplane.
The thrust acting forward equals the force the mass flow rate exerts rearward. Neither is the cause (action) nor the effect (reaction), since it's a two-body system (engine and air).

The forces are perfectly simultaneous, and are there for the same reason.

The energy bit:
Energy (work) equals force times displacement.
A non-accelerating plane in mid-air, or a jet engine running on a fixed test stand, still has moving parts and a moving [steady] exhaust: displacement is happening.
Since we can't create energy and it has to be conserved:
Let's say the total energy leaving the combustor (heated accelerated dense air) is 10 pirate-ninjas, then say 5 of which drive the turbine and all what's connected to it (including the air at the compressor). The other 5 leave the engine as an accelerated jet of air.
Say the compressor transfers 3 to the air, and all parts use 2 to rotate. The air comes with its 1 pirate-ninja of stored energy. The 3 gained by the air, now 4, meet the fuel in the combustor and release 10 (perfect lossless combustion, sorry). So, the energy stored in the fuel before combustion is 6.

(Own work)

The turbine-shaft-compressor is one body, the turbine absorbs 5, and transfers 3 of those to the air via the compressor, i.e., the engine parts absorb 2 to rotate, this is what you referred to as mechanical energy.

In other words—
The engine added 4 pirate-ninjas to the air from start to finish, giving the air added kinetic energy (mass flow rate), which translates to forward force as explained early on. In doing so, the engine spent 6 fuel, 2 of which to purely rotate the engine shaft, the other 4 went to the Δ mass flow rate.

The ratios above are not real, only illustrative. If you add more fuel, more energy will be released (excess oxygen is still available, that's how afterburners work), this energy will spin the engine faster, bringing in more air for a better efficient cool combustion.
The more efficiently the fuel energy is extracted, the more thrust we get. The properties of the air will have an impact; how dense is it, is the engine running on the ground, or is the plane transferring some of its kinetic energy into steady air resulting in ram-air energy, and so on.
So the ratios/percentages are not fixed, they depend on the operating conditions as well as the engine design (e.g., bypass ratio, compression ratio, etc.); even for the same type, different variants have different number of stages.


What is the equation for the energy balance between turbine, compressor and propeller?

Since the compressor loses a fraction of the turbine's work through the shaft, but is unaffected by the gearbox, but the prop experiences losses from the shaft and the gearbox, this equation should be what you need:

$$\dot{W_t}=\frac{-\dot{W_c}}{\eta_{shaft}}+\frac{-\dot{W_p}}{\eta_{shaft}*\eta_{gearbox}}$$

Which is the same as your attempt two (with some algebra).

As you add more efficiencies to a component, you would just continue to multiple the all $\eta$'s together to get the total efficiency of that component, since efficiencies are multiplicative and the associative property of multiplication.


Why does automatic trim exist only in the pitch axis?

The pitch requires trim because pitch is related to airspeed and engine power. As both of these change quite frequently (except for the cruising phase of a flight), it is convenient to adjust the aircraft's "natural pitch" during climbs or descends, or after changing flaps.

Most aircraft* will not exhibit a tendency to roll / yaw to one side in flight, hence, it is already stable in these axis and trim is not required.

Automatic yaw trim does exist on some multi-engine aircraft. When one engine quits, the flight computer will automatically adjust rudder to compensate the undesirable yaw due to asymmetrical thrust. On an aircraft without such system, the pilot must manually use the rudder pedals, and the amount of rudder has to be adjusted as engine thrust or airspeed changes.

* Small single-engine airplanes do exhibit roll and yaw moments due to the torque and p-factor of the propeller, but these aircrafts are marketed for affordable price and easy handling, so auto-trim is not implemented.


Was the intended purpose of the F-117 Nighthawk originally a stealth-fighter?

The short of it is that the "A" designation for a ground-attack aircraft has historically been a Navy distinction. The USAF/USAAF/USAAC has not traditionally differentiated between an aircraft designed for tactical ground strikes versus a dogfighter/interceptor. Most WWII-era Air Force planes were capable of both, and would be called "multirole fighters" in today's parlance (including the famous P-38, P-40, P-47 and P-51). Between WWII and the adoption of the 1962 Tri-Service Aircraft Designation System, the USAF used "F" almost exclusively for any one- or two-man aircraft performing either the air-to-air or tactical air-to-ground role (using "B" for aircraft intended for larger-scale strategic bombing). Thus, the "Century Series" aircraft, many of which were primary ground attack aircraft, all got the "Fighter" designation even when their mission profile was exclusively air-to-ground, such as the F-105 and F-111.

The Tri-Service Aircraft Designation System was patterned most closely to the Air Force's pre-existing system, but resetting all the counters (the Navy's system involved much lower numbers, many of which were grandfathered into the new system) and adding mission designations common in the other branches, including the Navy's Attack designation. The Air Force has more or less ignored many of the finer points of this system when designating its own aircraft; the A-10, and its A-X competitor the YA-9, are the sole airframes designed primarily for the USAF to carry the Attack designation (which is fitting as both planes were designed from the ground up to kill tanks and other armor). The other A-designated aircraft to enter service with the Air Force were Navy planes first (including the A-1 Skyraider and A-7 Corsair II).

The F-15E should, by tri-service rules, be designated AF-15E (emphasizing its modified mission of tactical strikes over its air-superiority pedigree). "F/A" as used for the Hornet is also non-compliant, and stems from an original desire to have separate fighter and attack variants of the Hornet which ended up being rolled into one plane. "FA" or "AF" would suffice not only for the Hornet, but also the F-16 Falcon and the F-35 Lightning II (yet another aberration, this time in the numbering, keeping the number from the X-35 tech demonstrator instead of being the F-24 as expected).

The F-117 is a very special case. The airframe received its designation after 1962 and so should have been designated either A-14 (as its mission has always been tactical ground strikes) or F-19 (keeping with the USAF's tendency to label any light offensive aircraft a "fighter"). Development of the F-117 from the Have Blue project was an open secret, and it is widely believed that the Nighthawk is the missing "F-19" in the U.S. numbering system (the F-20, a variant of the F-5 powered by a single larger turbofan, having been announced and demonstrated long before the F-117's existence was officially acknowledged), with the pre-1962 designation intended as misinformation.


What is the difference between a business jet and a regional jet?

I would say its not quite who operates but how its operated. A business jet is typically outfitted to carry a small number of people in a very luxurious way while a regional jet is outfitted to carry a lot of people a short distance.

No one even says business jets have to be small or of a select list of airframes, you can order a 747 business jet if you have the cash. Similarly no one says a regional jet has to be small, we are now seeing 747SR's doing short haul flights in Japan.

From a legal standpoint, the difference may be in the operation type as well. Scheduled regional flights here in the US will occur under part 121 while charter business operations will generally occur under part 135 if you own the plane the operation may even occur under part 91. This mainly has differences on inspection intervals for the airframe and some other operational related things. Assuming you can land the plane on the runway and depart again safely these don't limit where you can go.


A gust alleviation system is a control system fitted to some Fly-by-wire (FBW) aircraft that reduces the effect of gust loads on the aircraft by deflecting control surfaces such as ailerons, rudder and elevators.
The system works by measuring the upward acceleration of the aircraft and comparing that with the acceleration commanded by the (auto)pilot. A feedback loop adds a correction signal to the signals controlling the deflection of the control surfaces in order to counteract the accelerations cause by wind gusts.
In its simplest form the accelerations are sensed near the center of gravity of the aircraft. More advanced implementations work with multiple sensors in the body and in the wings. These gust alleviation systems do not only attempt to annul the effect of the gusts on the aircraft's normal (upward) acceleration, they also reduce the wing bending moments. This in turn reduces metal fatigue.
In the A380 the load alleviation system is nicknamed "valse des aileron" (Waltz of the Ailerons) because of the dancing movements of the aileron:


Is it OK to make an approach without any straight-in segment at all?

If the aircraft has not established a stabilised approach, a go around is required. According to EUROCONTROL's Skybrary, a stabilised approach is defined as:

  Their Approach-and-landing Accident Reduction (ALAR) Briefing Note 7-1 suggests that "all flights must be stabilised by 1000 feet above airport elevation in IMC and 500 feet above airport elevation in VMC. An approach is stabilised when all of the following criteria are met:

  The aircraft is on the correct flight path
  Only small changes in heading/pitch are necessary to maintain the correct flight path
  The airspeed is not more than VREF + 20kts indicated speed and not less than VREF
  The aircraft is in the correct landing configuration
  Sink rate is no greater than 1000 feet/minute; if an approach requires a sink rate greater than 1000 feet/minute a special briefing should be conducted
  Power setting is appropriate for the aircraft configuration and is not below the minimum power for the approach as defined by the operating manual
  All briefings and checklists have been conducted
  Specific types of approach are stabilized if they also fulfill the following:

  ILS approaches must be flown within one dot of the glide-slope and localizer
  a Category II or III approach must be flown within the expanded localizer band
  during a circling approach wings should be level on final when the aircraft reaches 300 feet above airport elevation; and,

  Unique approach conditions or abnormal conditions requiring a deviation from the above elements of a stabilized approach require a special briefing.

  An approach that becomes unstabilised below 1000 feet above airport elevation in IMC or 500 feet above airport elevation in VMC requires an immediate go-around.

(Source: www.skybrary.com)


How are airline pilots assigned routes? Are there easy and tough ones?

The answers to your questions vary greatly depending on the individual airline, type of equipment, what kind of flying they do, as well as contractual and union (if any) work rules. The one thing that is generally the same and as noted in the previous answer and comment, is that scheduled lines of flying are published to the crews, and a bidding system based on seniority is used to assign those lines.

  Also, can routes be classified into tough and easy?

What one pilot considers tough another may consider easy. A better way perhaps to think of it is that what one pilot considers desirable, another may not, and that will be reflected in how the individual pilots bid.

Some examples (but certainly not exhaustive): Young pilots with families would typically bid away from Christmas flying. I, however, not being a fan of Christmas and with all my children grown, deliberately bid to work on Christmas to open a no-work-on-Christmas line for someone else. In the northern hemisphere winter, I would bid into Australia, South America, or Africa because I don't like the short days of winter. In the northern hemisphere summer I tended to bid into places where I stood a good chance of getting to a beach. A lot of pilots bid simply to maximize income. And there were those who bid to maximize overnights at a place where they had an ongoing personal relationship.

Whether or not a pilot gets to actually fly a line as published is another matter. If you're flying for a scheduled airline that does no on-demand charter work, and you're going from one company station to another company station, chances are good that you'll get to fly the line as published. If, however, you're flying for a company that does on-demand charter work, the probability of flying the line as published goes down as the percentage of charter work goes up, and this is especially true with a mixed fleet of passenger and cargo aircraft. I flew for two commuter airlines, and I almost always flew my awarded bid line as published. Then I flew for two 747 carriers, both of which did a lot of on-demand charters. In the 12 years of flying for the 747 carriers, I rarely flew a line exactly as it was published. If was a matter of when you would have to depart from your line, not if.

There are companies that do nothing but on-demand charters. In those cases what you're bidding is not where you're going to fly, but which days you will be on-call.

  Doesn't more traffic in a particular area mean more tougher?

Some would consider it tougher, some more fun. A higher workload certainly, but I always felt that was more fun. There's something addictive, at least for me, to running approaches in high-density traffic. It's quite exhilarating really.


Is this Corrected Mass Flow equation correct?

The equations on Wikipedia are correct (see Flack, for example). I believe your error is in their interpretation. You say that you are given a mass flow rate and want to "convert [it] to a corrected mass flow rate at 10000 feet." But the direction you take the equations is as if you have a mass flow rate at 10000 feet and want to convert it to the mass flow at sea level. If the latter is what you intended, then I see no error. If the former, you need to invert the equation.


Why would a fighter use the afterburner and air brakes at the same time?

The first photo is from the Tornado Role Demonstration Team's display at RAF Leuchars in September 2012 (source).

That Sep '12 show or its preparation is on YouTube. Most of the instances of the air brakes as seen from the cockpit (looking behind) are followed by the swing-wing extending and the afterburner turning off (you can tell from the sound of the variable nozzle actuators).

While the photos are cool, I'd say it's just perfect timing before the pilot turned off the afterburner while slowing down.

Such example (above) can be seen after 7:40 in this video. Notice the wing position, and from the video notice the aforementioned sound once the wing is extended.

Another possible reason is slowing down for the spectators to see and hear the afterburner. That can also coincide with the fake bomb drop – a pyrotechnic wall of fire, the smoke of which can be seen in the first photo in the question (example below).

An RAF Tornado GR4 carries out a mock bombing run (BBC)


What are these wavy lines on fighters' canopy?

It is an explosive cord which helps to crack the canopy (pdf!) before the ejection seat has to do this all by itself. When ejection is commanded, the harness is tightened and the canopy is shattered, and only then the real ejection starts. Earlier designs would blow the full canopy off, but this takes longer than shattering it, especially when the canopy is large.

Some seats have their own canopy breakers, but thick, tough canopies which are needed for flying at high dynamic pressure and for surviving bird strikes would slow the seat down too much. The F-16 canopy is 12mm thick in the area above the pilot.

They are used widely for both land- and carrier-based aircraft, and modern designs try to make them less obvious. The F-35 canopy uses just one line down the middle.


Do commercial passenger airplanes have cambered airfoils?

I think it's safe to say that all passenger planes use cambered airfoils, although I wouldn't be surprised if someone finds a case of an aerobatic plane being used to carry a paying passenger, just to prove me wrong.

There's a fairly comprehensive list here. You'd have to look them up to be sure, but many of them use codes that indicate thickness and camber. For example, the first digit of a NACA airfoil is the camber.


What is the maximum altitude of barometric altimeters?

It depends on the altimeter's design and certification. An example for a  modern analog (aneroid) altimeter is this $5,000 Mid-Continent model.

Its certified range is -1,000 to +20,000 feet, this is a reading you can depend on. The actual mechanical range is -15,000 to +50,000 feet.

An RVSM altimeter working off multiple sources and an air data computer can take you higher. And an altimeter on an F-104 is probably even better.

A cheaper $150 model shows a certified range of 10,000 feet for one of the variants.