"Airplane mode" does not disable GPS... is it safe to use GPS in flight?

theoretically? GPS IS receive only. There's no way to talk to the GPS satellite network except using the big antennas of the network owners (the US DoD) and the communications are no doubt heavily encrypted.

Now, does that mean it's "safe" for aircraft electronics. Any receiving antenna does have an EM field around it, so if you believe the myth that those electronics are so sensitive and easy to jam that any EM field at all causes them to malfunction the answer is an obvious NO.
But that myth is just that, a myth. If they were so sensitive, that old walkman you were using in the 1980s during flights would have brought down that aircraft. Because not only do antennas have EM fields around them, any electrical device that's turned on has one (in fact any electrical cable with a current flowing through it has one, including the headphone cord for the in flight entertainment system).
And that GPS system in your cellphone uses a lot less power than that walkman, has a far weaker field surrounding it.

Of course it's theoretically possible that a strong enough EM field might interfere with the electronics in an aircraft, but then to you'd need just the right signal. Which would indicate you need intent (or incredible bad luck)!

Effectively the GPS in your cellphone is a lower powered version of the GPS receiver in the belly of the aircraft, which has its own antenna (which no doubt has a similar field around it, but of higher strength).


For a 180 degree turn after takeoff, what is the normal turn radius for the A320 and 737?

While in theory possibly a duplicate of the other question, and while the physics are very well explained there, the numbers to be used for takeoff and landing aren’t given in the other thread.

The following works as a rule of thumb for most commercial airliners: Maximum bank angle after takeoff with all engines would be around 25 degrees, with a failed engine it would be around 15 degrees until minimum clean speed is reached and the flaps are up and 25 degrees after that.

True air speed shortly after takeoff shouldn’t be much above 200 knots for most weights, airfield elevations and temperatures encountered except in extreme circumstances.

Plugging both these into the formula for turn radius explained elsewhere gives just above 2300m radius on all engines, and just above 4000m radius with a failed engine and before cleanup.

Brief answer, but I hope it helps!


How are turboprops and other propeller planes pressurized?

Turboprops are actually turbine engines. They can produce bleed air just like turbine engines (e.g. turbofan). The bleed air can be used directly to pressurize the cabin, or it can drive another turbo compressor to pressurize fresh air from the outside:

Modern aircraft with supercharged piston engines simply use bleed air from a) the main engine's compressor or

b) the main engine's turbo charger

Another solution is to drive dedicated air compressors to pressurize the cabin. Typically this may be Roots blowers or centrifugal fans. They are mechanically driven from the main engine(s).

Image source and more information on this topic: www.aircraftsystemstech.com


Should you immediately attain max glide speed after engine failure?

According to the amplified emergency procedures of the Cessna 172 Model N POH (emphasis added):

  After an engine failure in flight, the best glide speed shown in Figure 3-1 should be established as quickly as possible.

The same POH lists 65 KIAS as the best-glide speed.

Time spent away from best glide means less glide range. If increasing time, not glide range, is your goal then the minimum sink rate speed would be what you would want to fly. In an emergency, time and glide range give you more options.

The POH and physics agree: yes, establish best-glide speed immediately after an engine failure.


How much water does a passenger airliner carry?

It is going to vary according to flight mission, passenger count, season, or what part of the world the flight takes place.

Here are the capacities from a company document.

MD88/90 47USG (177.9L)
MD11 250USG (946.4L) Estimated

732/733 40USG (151.2L)
737 60USG (226.8L)
747 3x 110USG = 330USG
757 66USG (249.8L)-Fill valve closes automatically at 50USG (189.3L)
762/763 120USG (453.6L)-Fill valve closes automatically at 102USG (385.5L)
763ER 160USG (600.6L)
764ER 224USG (847.9L)
772ER 300USG (1135.6L)

CRJ 200/700 31.5USG (galley 8USG/30L, lavatory 5USG/19L, toilet 18.5USG/70L)

As mentioned, the term "potable" water seems to be a minor overstatement. Some companies warn employees to not uplift any potable water overseas (which means not outside the US, Canada, or UK). But based on what I've heard, I wouldn't drink it wherever it came from.

Why You Should Think Twice Before Drinking Tap Water

Why you should never drink water on a plane, according to a flight attendant

Airline's drinking water fails hygiene tests

The "potable" water is usually chlorinated water, but you´ll never know about the truck or tank service overseas. Usually the galleys contain an anti-biological filter (silver ions) for the taps and coffee makers, which get changed regularly. Also the tanks will be disinfected every few weeks, normally during an A-check. Part of a C-check is to remove and test them.

On a B737, the potable water tank is in the aft cargo pit behind the last wall under the aft galley just right in front of the pressurized bulkhead. The tank itself is made out of composite materials and fiberglass. The tank is about 4 feet long and 2 feet tall. The 737s only have one potable water tank.

The B747 has three 110 gallon filament-wound fiberglass tanks attached to the forward side of the center section front spar (rear bulkhead of the forward baggage compartment). The water is moved from the tanks by pressurized air. This pressure is provided by electrically driven air compressors mounted next to the tanks. Not all operators use all three tanks and some have deleted some tanks. 747 AMM, 38-11-00, page 1, pg 2.

Passenger MD-11 hold up to four 63USG tanks, the freighter usually has all removed except for one. This water also serves for flushing the vacuum toilets if installed. The tanks sit in the utility tunnels (behind the sidewall) of the forward cargo compartment.


Flight Design CTSW vs Cessna 162 (Light Sport Airplanes)

Don't have any personal experience, but having been around GA since the mid 70s, and looking them over, the CSTW wins hands down.

To have any kind of utility a 2 seater must have more than a 500lb useful load and the CSTW is over 600lbs based on a 701lb empty, although airplanes you find used will always be heavier, probably around 725 to 750lbs empty.  Still that's a pretty impressive useful load. Even if you don't care too much about the useful load because you fly by yourself all the time, at some point you will.

Any Skycatcher you find is going to be 875 lbs empty or more, with more or less the same gross (just about any airplane you buy used is quite a lot heavier than the published factor number as they pick up a pound here and a pound there from this and that over time).

Carbon structure, so no metal.  Made in Europe.  And the 912 family has proven to be a very reliable engine line.

So between the two, the Flight Design.  I wouldn't touch a Skycatcher, which has had structural issues where Cessna had to go out modifying wings, and it kind of has that taint of failure to it due to Cessna just kind of abandoning the program even though they had a fat order book (Almost certainly because they discovered they were losing money on them even with production in China).  Which is why they're cheaper.

Bottom line though is you must go for a ride in each to make an informed decision.


How much air is recirculated (vs. bleed air injected) in modern airliners cabin?

From an own work report, based on public web presentations for type rating and on The Boeing 737 Technical Guide by Chris Brady:

  A recirculation system reduces bleed air requirements and pack loads, by filtering cabin air and re-introducing it to the mix manifold. Approximately 25% of the cabin air is recirculated. The recirculation fan will switch off if either pack is in HIGH flow, causing a net reduction in ventilation rate of about 15%. Total ventilation rate on a 737-800 is approx 1 m3/sec

  A portion of the conditioned air from the left pack flows directly into the flight deck. The remainder of the left pack air, all of the right pack air, and air from the recirculation system is combined into the mix manifold. Mix manifold air is distributed to the passenger cabin through different zones, via the side-wall risers on the left and right sides of the aircraft. On ground, pre-conditioned air can be pumped directly into the mix manifold

The B737 Technical Guide further mentions that on the B757 and B767, up to 50% of cabin air is recirculated, and on the MD80 none.


How do I calculate the heading to steer in this example?

You are holding 215 by compensating for a crosswind using 5 degrees of heading change.

The opposite of 215 is 035.

You must compensate by holding 5 degrees of heading change past 035.

Presumably, the fact that you're 30 minutes flight time away from the VOR when you turn gives the pilot sufficient time to reestablish themelves on course. Thanks @MichaelHall!


When aircraft fly inside clouds, they fly under "instrument rules". It doesn't matter whether the visibility is reduced (at night) or totally blocked (in a thick cloud), this mode of flying simply assumes the crew has no external visual reference, they fly solely using indications given by on-board instruments.
The following short video shows a situation frequently encountered, the crew doesn't see anything outside prior to being so close to the ground, they are nearly landed.

Landing without visibility, source: YouTube.
After the problem of replacing external references has been solved, the next most important issue is to safely stay away from other aircraft. To prevent collisions, pilots are supported by air traffic control (ATC) from the ground. ATC determines aircraft location and altitude by relying on an on-board transponder. ATC issues appropriate information and instructions for pilots in order to maintain aircraft separated.
Should ATC fail to separate aircraft, commercial aircraft are equipped with a safety net: In last resort, close aircraft, transponder-equipped, are detected and avoided by an on-board collision avoidance system. While this system is efficient when there are only 2 or 3 aircraft involved, the escape maneuver must be done quickly and can be therefore sharp enough for a passenger not belted to be injured. This doesn't work if the other aircraft isn't equipped of a transponder, but all commercial aircraft carry such equipment by regulation.
All large airliners we know fly under instrument rules, regardless of the weather, or the time of day. However for a few runways, landing can be done  by a circling maneuver (or circle-to-land maneuver) in which the crew approaches the runway using an instrumental guidance which is interrupted before landing (usually because the guidance is designed for another runway), leaving the crew under visual rules until touchdown (such maneuvers are known to be more hazardous).
For the sake of completeness, a special kind of visual flight, VFR Over The Top, may be allowed over the cloud layer, during the upper part of the flight, where the horizon and other aircraft can be seen.

1. Technical aspects of instrument flying
It's technically possible to fly inside clouds, fog, snow, at night, etc, but this type of flight is regulated, it requires technical elements both in the aircraft and on the ground, and mandatory additional training for the pilot.
Good sense, and regulation, require the pilot to be able, at any time, to:

a/ Maintain an aircraft safe attitude (flight conditions preservation),
b/ Avoid obstacles and other aircraft (collision prevention),
c/ Find their way to a landing aerodrome (navigation).
d/ Know where they are (position awareness),

Flying without visibility basically means knowing how to carry out these tasks without looking outside the cockpit.
A: Maintain a safe attitude
One of the main references a pilot needs is the horizon. When the horizon is invisible, An artificial horizon reproduces the horizontal plane using a gyroscope. This instrument indicates whether the aircraft is pitched or rolled.
Regarding altitude and speed, the same instruments are used both for visual and instrument flying: Barometric altimeter and airspeed indicator.

Main instruments, traditional presentation. Source: Aircraft Spruce
Image above (left-to-right, top-to-bottom):

speed, attitude (artificial horizon), altitude,
turn indicator, heading, vertical speed

Same instruments on the electronic primary flight display of a A330. Source
Being aware of the aircraft attitude without external visual clues is not natural and more difficult than usually expected. There was a famous study (180-degree turn experiment, Bryan, Stonecipher, Aron) in 1954 which showed a pilot not trained to fly with instruments loses control of the aircraft in 3 minutes in average if external references are lost.
B: Collision prevention
As mentioned, a collision prevention service is provided by radio from the ground. An aircraft flying without visibility is separated by air controllers (ATC) from all other aircraft. The exact type of separation provided varies with airspace category, in particular when radar coverage is missing, e.g. when flying over oceans. For EU countries, see Classification of Airspace at SKYbrary.
Civil ATC determines the aircraft location and altitude by interrogating a transponder on-board the aircraft, from the ground. Should the aircraft transponder be not cooperative, ATC might have access to a primary radar, and perform traditional echo measurement, which is less accurate. Primary radar stations are usually operated by military.

Typical ATC room, source: Learn To Fly Here

See also What is a TRACON? for a full description of control rooms in the US.

ATC is definitely a difficult four-dimension task done using 2D displays. Mistakes are made, most of the time they are fixed in time. In the picture below, VRG231 is descending from FL370 while the facing and climbing DCA337 is through FL262. ATC evaluates they will cross safely, but overlooks the closer XCM3018 approaching from the right at FL360 (more details at SKYbrary).

Loss of separation conditions in place: VRG231 is descending. ATC takes DCA337 into account, but overlooks XCM3018, source
Additional on-board equipment can be used for actual nearby aircraft detection. Such collision avoidance system, known as (TCAS or ACAS), detects transponder-equipped aircraft, typically only within a few minutes radius by using a technique similar to ATC interrogation. In addition, TCAS can provide coordinated conflict resolution advisories to the pilots, to increase separation and prevent collision.

B737 TCAS (TA/RA positions on the transponder panel). Source

C: Navigation:
After the two first tasks of the crew (aircraft in safe flight and collision risks under control), it's time to look at how the crew can reach the destination.
Navigational radio aids are positioned at important locations on the ground, and on-board instruments are used to take benefit of them. Today they include VOR (relative bearing determination) and DME (distance determination) for navigation to, from and between airfields. NDB are still used, but their decommissioning has started around the world, they are used as long distance and non-precision VOR.
Extract from Nice airport (LFMN, France) documentation for Runway 04 departures. Note how VOR (circled in green) and NDB (magenta) are used as waypoints. Also note how NIZ VOR-DME is used as a reference for relative bearing and distance (green stars).

Source
Space radio aids, namely GNSS (US GPS, EU Galileo, Russian Glonass...) are complementing or replacing ground aids for operations (ground aids are still used and required by regulation). For example, the same departures from Nice using Precision Area Navigation (P-RNAV) taking advantage of GNSS, inertial and ground aids to obtain a precise combined position:

Waypoints are not referring to any ground aid but defined by their coordinates in the flight management system database. Same source
A manual or an automated landing can be conducted with the guidance of an ILS (instrument landing system), which is a radio lighthouse usable to follow proper direction and proper slope:

ILS principle (magenta clues displayed on the pilot panel)
As you may have noticed, contrary to a persistent belief, pilots don't rely on ATC for navigation (the exception would be when a pilot has lost all instrumental references. ATC may usually be able to provide a position if the transponder is still operational).
In busy terminal airspace, typically around large airports, ATC role is extended. First, the risk of collision being large and airports being in densely populated areas, aircraft must follow more constrained paths, ATC operators constantly monitor these paths and request corrections from pilots when necessary. Second, runways are scarce resources, arriving aircraft (and departing aircraft to a certain extent) must be sequenced (e.g. by adjusting their speed) into orderly and dense landing queues.
D: Position awareness
Current horizontal position has been determined for a long time using VOR and DME and geometry: angle-angle (aka triangulation) or angle-distance equations.
Larger aircraft have also used inertial platforms which are able to provide no only the current position, but also the heading, the ground speed and most uniquely the acceleration, the rate of rotation and the attitude (from which the angle of attack can be obtained).
Today, those technologies are complemented by GNSS which is able to provide the current position and altitude.
The inertial platforms are still used for their complete independence from any external resource, and their precision which is better than GNSS in the short time. Their big con is they drift continuously and must be reset at intervals (e.g. using GNSS data). To take advantage of everything available, sources are often mixed to provide weighted values and cross checking (add to this air sensors providing altitude and airspeed data).

B737 Fight Management Computer page showing current position according to several sensors. Source
Aircraft are also equipped with ground detection, to help prevent so-called "CFIT", controlled flight into terrain. This sensor is based on on-board radar and stored maps and display ground obstacles around. It is used for horizontal monitoring (hill, mountain) as well as vertical monitoring (ground proximity during landing). Such systems are known as EGPWS, enhanced ground proximity warning system.. They warn pilots by loud advisories, e.g. "Terrain! Terrain, pull up!".

VSD/EGPWS display on Boeing aircraft, source

2. Regulation point of view
Visibility conditions are determined to be either visual (good visibility) or instrument (insufficient visibility) and there are two sets of rules when flying (visual and instrument). Flying in instrument conditions requires by regulation to perform the flight under instrument rules.
Flying with reference to instruments only, requires:

The pilot has received the proper training,
The specific equipment is available in the aircraft, and on the ground,
ATC is provided from the ground.

VMC vs. IMC
There is a set of minimum conditions to declare that the outside environment is visible: these conditions are known as Visual Meteorological Conditions (VMC).
When VMC are not achieved, the conditions are said to be IMC, for Instrument Meteorological Conditions.
VMC criteria depends on countries and airspace, though ICAO provides international recommendations, e.g. in France, generally:

Minimum horizontal visibility 5 km (8 km above FL100).
Minimum distance to clouds: Horizontally 1.5 km, vertically 1,000 ft.

VFR vs. IFR
Any flight must be done under one of the two existing sets of rules:

Visual Flight Rules (VFR)
Instrument Flight Rules (IFR).

The rules to be followed are dictated by regulation and are directly dependent on the meteorological conditions.

In VMC, both VFR and IFR flight are allowed.

In IMC, only an IFR flight is allowed, the pilot must be qualified to perform IFR and the aircraft must be certified for IFR.

Related:

Spatial disorientation which may lead to fly upside down without knowing. Related training.


Lockerbie bombing - amount of debris (confusing numbers)

Pieces of wreckage implies a large 'section' of plane, whereas debris suggests miscellaneous smaller items and bits of metal etc.

I agree it's potentially confusing, however, and likely arises from two people editing the same section without adjusting the context.

I'd say that 4 substantial sections of plane were found, along with a large amount of smaller debris scattered around, totalling around 10,000 pieces.


Are there examples of passengers' Micro SD cards or USB flash drives surviving crashes?

Yes. Some videos where recovered from the germanwings crash. See this article talking about it: link

The video can now easily be found online. I recommend against it tho.


How much time do pilots have to execute a TCAS Resolution Advisory?

It depends a bit on speed but your linked article has the answer

Traffic advisories are provided 35-48 seconds out and a Resolution will be provided 20-30 seconds out. Since the resolution is coordinated you only need enough time to clear the other aircraft however the greater separation the safer it will be so its advised to respond immediately upon a resolution being provided. Immediately means as fast as possible.

The FAA's TCAS II outline document states that modeling was performed assuming the pilots responded within 2.5~5 seconds

  In modeling aircraft response to RAs, the expectation is the pilot
  will begin the initial 0.25 g acceleration maneuver within five
  seconds to an achieved rate of 1500 fpm. Pilot response with 0.35 g
  acceleration to an achieved rate of 2500 fpm is expected within 2.5
  seconds for subsequent RAs.


How does the idle mixture adjustment in a Stromberg NA-R9B float-type carburetor work?

The temp is nominally 68F, but the acceptable range is 40 to 80 ambient, by practice.

I can't say about that specific carb, but generally in the Stromberg and the SUs, there is a needle, which can be raised and lowered, which changed the metering.  By changing the taper of the needle, you can also change the mixture profile through the venturi flow rates.

We used to use a manometer to get the vac reading, and then look at EGT to make a decision on mixture.

The needle height will impact the overall mixture, and the shape of the needle will impact the mixture through the flow range.

What aircarft is this on?  I know some of the J-3s had Stromberg carbs, but this specific carb model is not ringing any bells on aircraft.


Why does the IL-76 have a lump at the bottom of its nose?

The 'lump' holds a ground surveillance (mapping) radar.
IL-76 has two radars: the usual meteo radar in the nose and the ground surveillance radar (primarily for navigation). In addition to that, like all contemporary Soviet long(er)-range transports (esp. military ones), it has a dedicated navigator position with the glassed 'verandah' for better view of the ground.
Most commonly, this navigator position took up the nose cone space that is (nowadays) usually reserved for the radar. If you look at most modifications of Tu-134 or Tu-114, you'll see they have a similar (but smaller) 'hump' underneath to house the meteo radar. But the widebody IL-76 could afford both the nose radar and the navigator station under it, plus a dedicated mapping radar.
The navigator's seat and equpment don't extend much below the lowest window, so most of the space is used for the radar rather than the navigator.


Can a change in altimeter setting make you change the airspace?

No, fiddling with your altimeter setting doesn't change the airspace you are flying in. So you can't bust the class A above 18 000 ft by changing the setting. The top and bottom boundaries of the airspace are defined by applying the altimeter setting local to that airspace.

Conversely, and perhaps more important, you can't weasel out of a busted airspace by quickly changing your altimeter setting.

Your transponder sends your altitude as if your altimeter was set to 1013.25 hPA / 29.92 inHg, regardless of what your actual setting is. The ATC system will do the conversion according to their setting, so you can't fool them.

Note that the altitude resolution of your transponder is either 100 feet (Mode C) or 25 feet (Mode S with appropriate altimeter encoder), so 1 feet difference doesn't really matter.


Those wings are from an ERCO Ercoupe. The diagonal ribs are very distinctive.


How airlines are calculating crew member's payroll?

As mentioned in the comments, this is different per airline. I'll list some of the options used, though there may be airlines out there with their own unique system not included in this list. Note that I use Flight Attendants as examples, as their payroll information and training requirements is a bit more "open source", but these pay methods carry over to anyone working in the aircraft.

Hourly:

This is by far the system of choice for the larger airlines, as they are more easily able to track performance and efficiency statistics (hours worked v hours needed v pay per hour), as well as the fact that it often ends up being cheaper. Flight Attendants have seen remarkable raises in recent years for most companies, and can make anywhere from $25-60/hr, depending on how long they have been working with that particular airline, or in that particular occupation. This provides an incentive for sticking with your current employer.

Static Salary:

A static salary is similar to what you would find in a regular job. You have a minimum number of hours expected of you, and you get paid a flat rate. In the interest of keeping your job, you would be expected to work many more hours than the minimum, as cabin crew understandably work different amounts each month.

Dynamic Salary:

A dynamic salary is a mix of the above two, and is more of a European method. This type of pay expands or shrinks depending on your hours. There is a maximum number of hours you can work, but a relatively low minimum. If you hit the maximum number of hours, or more, you will receive 100% of your salary. If you work half the number of hours, you receive 50% of your salary, and so on. These salaries are typically much higher than a static salary, but it averages out to about the same as a static salary.

Trips for Pay:

TFP is not the easiest way to do it, but gives the airlines a way to pay the lowest wages! You get paid "per trip", as long as the trip hits the minimum distance to count as a trip. If not, you earn a fraction of "per trip" pay. Depending on the airline, a standard trip is typically between 200-300 miles. If the trip is longer, you get paid an additional rate per mile. This system also tracks time that is blocked off for your duties, so you will still get paid if you are waiting for your next aircraft to arrive, but it is a much lower rate.

Extra Pay:
On top of all those methods of pay, nearly all airlines provide some form of additional pay that is added either per trip, or per month. This can be for special skills or training that a flight attendant has received, or for working through holidays or red-eye flights.

That said, I spoke with an old 747 pilot in my family, and he mentioned that holiday pay is not all it's cracked up to be. He was used to them calling in  pilots to work every Christmas Eve, so he ensured when he got out of work on the 23rd, he would take a swig of brandy as soon as possible so that they couldn't legally force him to work extra hours!


Could compressor stalls be caused by air in supercritical conditions?

The answer to your question:

  Is it possible that supercriticality of the fluid (air) is one of the causes for compressor stalls or compressor surge ?

...is definitely no.

Stall is caused by an excessive angle of attack of the incoming air, relative to the blade. It can happen on the first stage (first row of rotating blades), where the pressure is no where near high enough to be supercritical. Surge occurs when the stall is very severe, so it’s the same phenomenon, just worse.

While the likelihood of a stall occurring is determined by measuring the total pressure distortion across the compressor face, it is the angle of attack that is the critical factor. Regions of low total pressure indicate the flow is likely to be turbulent in these regions, and therefore the angle of attack is not steady, and can exceed the ability of the air to follow the surface of the blade. Once it separates, it becomes turbulent, which means the blade does not perform its function of compressing it well. This is a big problem, as the compressor is trying to get the air to flow “uphill”. Stall generally starts as a phenomenon involving a few blades on one or more stages. It can then develop and cover a large section of the compressor. If the axial velocity of the flow through the compressor starts to vary, faster and slower, then faster again, it is called surge. The engine “chugs”.


Could an ultralight hypothetically takeoff without power on if it were windy enough?

It could, but eventually drag would cause the ultralight to start moving in the same direction as the wind and it would lose any apparent forward airspeed.


Is the war pilot obligated to fly the same plane daily or must he change the plane according to every required mission?

Of which type of pilot are you asking:

Student
Military
Private (hobbyist)
Corporate
Airline

I will be using the term licensed to loosely mean certificated, current, and proficient with the proper endorsements and documentations.

The short answer is no. They are not obliged/obligated to fly the same aircraft. The pilot can choose to fly in any aircraft they want. They will more than likely choose an aircraft that fits their mission.

The long answer depends on the mission. This might determine if the pilot gets the opportunity to fly at all. Or, what “mission” (job, employer, flight school, opportunity) they choose to seek. But, all aircraft fly a differently from each other. In the same make and model, the differences may be slight. In the same category and class, the differences may be very challenging. In different categories, classes, and types, the differences may be too great to overcome without specific training.

Students:
Most instructors will want their students to stick to one type of aircraft for their initial training (first 35-80 hours). That does not mean it will be the exact same aircraft. Large schools may have several identical aircraft of the same make, model, and avionics (when possible). The students will be expected to fly whichever aircraft is available at the time of the lesson. Although, the instructor can endorse the student to fly solo in any aircraft the instructor feels the student can handle on their own. This is essential in developing habits, muscle memory, and structure.

After initial training, the student (then private pilot) is then only limited to flying the same category and class of aircraft in which he/she was trained. Although he student can seek training in another category and/or class. I flew both single engine land airplanes, and helicopters.

Private (hobbyist):
A private pilot can fly any aircraft for which they are properly licensed. The license will only stipulate category and class of aircraft for which a type rating is not required, type rating, and other flight category ratings. Type ratings are usually required for large and/or turbine aircraft. Some other ratings are based on flight categories (VFR vs IFR). There are some restrictions based on medical requirements. And, some flight categories will require specific endorsements (tailwheel, high altitude, high performance, complex, aerobatic, etc.) They can also fly in aircraft for which they are not properly licensed if a properly licensed Pilot-in-Command is also flying at the controls.

There is a class of hobbyist pilots who are very limited in the type of aircraft that they fly. These pilots need endorsements for any aircraft outside of their specific category, class, or type of aircraft.

As a practical matter, a hobbyist pilot may fly several aircraft based on availability. There are flying clubs and aircraft rental companies that give pilots access to aircraft as they wish. Provided the pilot has the proper license and is able to perform adequately on a flight evaluation. I regularly fly several different Piper Cherokee varieties, Cessna 150/2, 172 and 182 varieties, SportCruisers, Robinson R-22s, etc. Availability and cost both play a factor.

Corporate & Airline:
Generally, these types of pilots will hold type ratings in specific makes and models of aircraft. Since it is a pretty large expense to maintain currency of these type ratings, which ones they will be able to exercise might be limited. Which specific aircraft they fly within their license requirements will be up to the needs of their employer at that time. They may fly different aircraft day by day, or even flight by flight on the same day.

These pilots can still exercise the privileges of their private pilot certificate and many do. In which case, they are free to fly any aircraft for which they are licensed. Their employer may limit them to only fly on a for-hire basis for the employer, solely. That does not limit them from flying as a hobbyist.

Military:
The military is going to determine which aircraft the pilot flies. It is the military after all. What the pilot flies is going to be based on the needs of the military. The pilot can make requests. But, being in the military means that the pilot has volunteered (in the U.S.) to do what they tell him/her to do.

Generally, that is going to be mission and budget based. The military will train the pilot for a specific type of aircraft, for a specific type of mission. If the pilot or aircraft does not suit the mission, they use a different pilot. If the military chooses to use the original pilot, they send them back to training for that specific aircraft, for that specific mission.

Both the trained pilot and the aircraft they are flying are very valuable assets. They are expensive tools that the military will handle with care (sort of). Mistakes cost lives and money.

What this means from a practical sense is that a pilot will not flip-flop between types of aircraft. There would have to be a very compelling reason to do so (like change of duty station or aircraft inventory). For the most part, the pilot will be assigned a specific individual aircraft unless the mission dictates otherwise. After all, it is their weapon. They must be proficient with it.

Think of it this way. You are not obliged/obligated to drive a certain car. You drive the car that fits your needs and budget. But then again, you are not obliged/obligated to work for an employer who may require you to drive a certain company vehicle.


How efficient would an airliner be if it did not have to carry its own fuel?

Short answer is about twice as efficient for a mid range route,(3000 nautical miles) when based on fuel used per ton of cargo per mile traveled.

Explanation:
I will use the 737-400 as an example because I have an operational manual for it. First we need to define terms. I assume we are talking about fuel burn per something: per mile, per hour, or per payload ton-mile. Gross weight is the total weight if you set the plane on a scale in some flying condition. Max gross weight is the maximum weight at which the aircraft is considered safe to fly. Operating empty weight is the lowest gross weight achievable in a flying condition, no cargo, no extra crew or passengers, and no usable fuel. Useful load is the difference between max gross weight and operating empty weight. Payload is useful load minus fuel load and extra crew.(that is load that pays, aka cargo and passengers)

The thrust required(and thus fuel consumption) for level flight is determined by aerodynamic drag and the majority of drag is broken into parasitic drag and induced drag; parasitic drag comes from shape or texture and dynamic pressure,(basically speed if you keep the density constant) go faster get more parasite drag, this does not change with gross weight.

Induced drag is caused by the lift created by practical wing designs, for a set wing design and speed the induced drag increases with weight. So high gross weights have higher induced drag and so require more thrust.

Now for the example. A 737-400 has a maximum gross weight of 143500 pounds and a typical operating empty weight of 77100 pounds(typical airline equipment with seats and such) giving a useful load of 66400 pounds. This weight can be split up however needed between fuel and payload depending on the length of the flight.(In practice other factors can limit gross weight such as available runway length, and payload as some engineering optimizations assume a lower landing weight than takeoff weight to save on structural weight.) At least up to the limit of installed fuel tank size, this model can hold 37708 pounds of fuel.

Some reserve of extra fuel is required for safety, diversions, holding and such, so this is usually extra fuel at landing. This is typically 4000 to 9000 pounds depending on specifics of the flight.

Assuming flight altitude of 33000 feet and mach .74 cruise(430 knots). I am using nautical miles and short tons(2000 pounds) for all of this.

A the most exaggerated case will be maximum range with reserve fuel of 9000 pounds.(maximum fuel at start, reduced payload) Payload will be at most 28692 pounds or 14.3 tons. Fuel burn at the start will be 6234 pounds per hour for 1.014 pounds fuel per ton-mile of payload (6234/(14.3*430), and at the end of flight 5066 pounds per hour for 0.824 pounds fuel per ton-mile of payload (5066/(14.3*430). (geometric mean of .914 pounds fuel per payload ton-mile. Change in rate is non-linear.)

If all of the useful load could be used for payload as in the case of an external fuel supply, or an infinitely short flight with no reserve fuel, you get 66400 pounds or 33.2 tons of payload. The fuel burn will still be 6234 pounds per hour but you get .437 pounds fuel per payload ton-mile. 6234÷(33.2×430)

So cruise fuel consumption with an external fuel supply will be approximately .437/.914 = 47.8% or about half of the fuel consumed per unit of cargo. Actual results will depend on variables if I must state the obvious. Longer flights would see more improvement, shorter flights less, payloads less than maximum allowable will also see less improvement, flights requiring less reserve fuel will also see less improvement.


Clarification on flight hours as compensation

There are a few different questions in here, some are FAA regulated and some are a matter of the terms of your employment

  If I have a CPL and fly for hire, paying no expenses of the flight,
  are my flight hours considered compensation in addition to my wage?

Maybe, its somewhat up to your employer, but more importantly its not really what the FAA cares about. You have a CPL and are presumably flying for a legal carrier/operation. In the eyes of the FAA they don't much care how you are paid beyond that. Practically the legislation is more to ensure that people who are getting paid are properly licensed and working for a proper operator.

  Do I have a legal right to those hours?

As Juan notes if you were PIC (or SIC) properly certified in the aircraft then the time is yours.

  Is a company allowed to, as a condition of employment, require that I
  don't log hours while flying their aircraft?

That seems like it would be encouraging you to not follow a FAR which is not a great idea.

  If a company suddenly and without reason sticks me behind a desk
  instead of having me piloting an aircraft, would the loss of flight
  hours be considered a pay cut?

This depends two things, your existing contract with your employer, and if that contract changes when your job changes. Often times with a role change your contract, or the terms of the original undersigned contract can be changed. If you were a pilot with a Minimum Monthly Guarantee in your contract you may be entitled to keeping your pay-rate. However if the new job comes with a contract change or shifts where you are under your current contract you may not be entitled to anything.


There are no keys to anything on a modern airliner. You just get in, hit the switches and go.


How does FlightAware correlate flights to Part 91 flight plan data?

The data that FlightAware first receives for most commercial flights
  is sometimes delivered a year in advance via schedules published by
  the airlines. That data then usually remains unchanged until a few
  hours before the flight. Pilots or air traffic control operators
  controlling airspace on the route of flight will push out new data
  with a flight plan that provides specific details about the planned
  routing, altitude, and speed of the plane. But that’s where the static
  data end and the real-time data begin.

  “When the door is shut and the parking brake is released by the
  pilots, the aircraft or airline will send us an ‘out’ message that
  indicates it’s pushed back from the gate, and we know that departure
  is imminent,” says FlightAware’s Baker. “As soon as the weight is
  lifted off the landing gear, we often get an ‘off’ message from the
  airlines or the aircraft itself that indicates the plane is airborne
  or a departure notice from air traffic control.”

  Once en route, FlightAware continues to get position updates from the
  plane via radar installations at air traffic control centers and via
  ADS-B, along with continued updates on the plane’s route from air
  traffic control. All of this information is then fused together by
  FlightAware’s software, which uses it to determine the plane’s
  estimated time of arrival, and then displays the aggregate data for
  the flight on its website and in its apps.

  “We detect the landing either by seeing the plane slow down below
  flying speed, by getting an ‘on’ message from the airplane, or by
  receiving an arrival notice from air traffic control. From there, we
  may have surface coverage to track the taxiing on the ground, and
  eventually receive the ‘in’ message from the airline indicating it’s
  safely parked at the gate,” says Baker.

  Now multiply all the above steps by the thousands, or one for each
  plane in the sky across the world at any given time, and you’ll begin
  to appreciate the amount of data that fight tracking websites’ servers
  and algorithms are crunching each and every second.

  https://www.fastcompany.com/3044490/how-flight-tracking-apps-work


If an airline cancels an aircraft order, can a different airline acquire those options?

In general yes, but depending on how close the aircraft was to completion they have to live with a different cabin and cockpit layout than what they are used to or would had ordered themselves.


Why is there an ETOPS marking on the nosewheel door?

You're correct that it is for ground handlers; more importantly, it is for mechanics. It is important to identify the aircraft as ETOPS as the servicing and checking requirements are different for ETOPS and non-ETOPS aircraft. For ETOPS aircraft, two critical systems (like engines) should have differnt maintenance personnel to avoid them making the same mistakes in both of them.
From 14 CFR § 121.374 Continuous airworthiness maintenance program (CAMP) for two-engine ETOPS:

(c) Limitations on dual maintenance.
(1) Except as specified in paragraph (c)(2), the certificate holder may not perform scheduled or unscheduled dual maintenance during the same maintenance visit on the same or a substantially similar ETOPS Significant System listed in the ETOPS maintenance document, if the improper maintenance could result in the failure of an ETOPS Significant System.
(2) In the event dual maintenance as defined in paragraph (c)(1) of this section cannot be avoided, the certificate holder may perform maintenance provided:
(i) The maintenance action on each affected ETOPS Significant System is performed by a different technician, or
(ii) The maintenance action on each affected ETOPS Significant System is performed by the same technician under the direct supervision of a second qualified individual; and
(iii) For either paragraph (c)(2)(i) or (ii) of this section, a qualified individual conducts a ground verification test and any in-flight verification test required under the program developed pursuant to paragraph (d) of this section.

In the same vein, from Boeing:

Strategies for Avoiding Multi-Engine Maintenance Errors
After investigating several multi-engine maintenance events, Boeing identified a key strategy for avoiding multi-engine maintenance error: If possible, operators and repair stations should avoid performing maintenance on multiple engines using the same personnel during a single maintenance visit. Following this strategy should also minimize the potential that improper maintenance will occur on redundant or backup critical systems, such as flight controls, electrical generation and distribution, and hydraulics.

If the NLG doors have ETOPS written on them it would be easier for the technicians to identfy the aircraft and perform checks/maintenance as required, using two different operators, if required.


What throttle setting does an airliner use while cruising?

(Above is the max cruise limit in standard ISA for the A320.)

It's 80.4% - 86.5% for the different weights and altitudes. Do note that 81% does not mean 81% of the available thrust. The maximum continuous thrust (MCT) at standard temperature is between 86% and 89% for the different cruise flight levels.

The colder the air, the lower the values, and vice versa for hot temperatures. If too hot above ISA, max flight level is limited for the higher weights due to MCT being the limiting factor.

For the A320 example, the thrust levers remain in the CLimb detent from thrust reduction to just before landing in normal operations.

For the 777-200, the range varies from 69% - 96.8% depending on the flight level and weight (with 86.8% - 94.7% being the optimum range). The wider range is due to the 777's wider payload/fuel range when compared to the smaller A320.


Why don't the newest versions of Mi-35Ms have retractable gear?

Quick answer: because Russian engineers don't like fancy stuff ;)

Long answer:

Fixed landing gears are common on helicopters even very recent ones, just look at French helicopter Tigre, Italian mangusta or American black hawk.
It offers a very lightweight and robust solution for landing while allowing easy ground maneuvers and also offers crash absorption.


Pitching moment as a pure moment and its measurement with a homemade force balance

There are better physicists than I at this site, but seem to remember a solution proposed in a wind tunnel test with load cells as follows:  Do the measurements separately.

Lift could be measured at the center of lift using only support 1.  C lift could vary with AOA (data points are generated one at a time from C lift at a given AOA).

Pitching moments could be measured using support 2 only, with the wing pivoting on its AC
(which could be some type of axle).


Is there a difference between how commercial jets and GA aircraft use airways?

In Europe, some airways are only available in certain flight level ranges, so a commercial airliner and a GA turbo-prop travelling from the same departure airport to the same destination airport could be travelling on different routes due to airway restrictions in place and the inability of one aircraft to climb to the same level as the other. Below the routing for PC12 operating IFR at FL150 and an A320 operating at FL250.

(FPL-DEXAM-IG
-PC12/M-SDE1FGHIJ1RWXY/LB1
-EDDL1000
-N0160F150 KUMIK L603 KOSEK Z74 HAREM T104 ANORA
-EDDM0150 EDQT
-PBN/A1)

The above flightplan from EDDL to EDDM validates for FL240, but anything above FL245 will not pass, it will error out with:

PROF195: KUMIK L603 KOSEK DOES NOT EXIST IN FL RANGE F245..F999
PROF195: KOSEK Z74 HAREM DOES NOT EXIST IN FL RANGE F245..F999
PROF197: RS: EDUUFFM14 EDUUFUL13 EDUUNTM13 EDUUTGO13 EDUUSLN13 EDUUWUR14:F245..F255 IS CLOSED FOR CRUISING REF:[EUROED41A] ED AIP(ENR3.3 1 NOTE 9)

To fly the same flight in higher levels, you would need another routing:

(FPL-DAXAM-IG
-A320/M-SDE1FGHIJ1RWXY/LB1
-EDDL1000
-N0260F270 DODEN Y853 BOMBI T104 ANORA
-EDDM0150 EDQT
-PBN/A1)

This routing works fine for anything above FL245, below it would again error out with:

PROF195: BOMBI T104 HAREM DOES NOT EXIST IN FL RANGE F000..F245
PROF204: RS: TRAFFIC VIA DODEN Y853 BOMBI IS ON FORBIDDEN ROUTE REF:[ED2318A] Y853 DODEN BOMBI
PROF205: RS: TRAFFIC VIA DODEN Y853 BOMBI:F000..F245 IS OFF MANDATORY ROUTE REF:[ED2318B] Y853 DODEN BOMBI
ROUTE135: THE SID LIMIT IS EXCEEDED FOR AERODROME EDDL [EDDL50120A] CONNECTING TO DODEN


How can seagulls slide in the wind without flapping their wings?

I've never heard of other birds than albatrosses do dynamic soaring, but since this is over land, it can be simpler ridge soaring—as the sea breezes hits the shore (and obstacles on it), it turns upwards and the birds simply fly in this updraft. They are flying against the wind and gliding down relative to it, but when you add the speed of the wind, they may be stationary relative to the ground—or zig-zag from side to side if the wind speed is a bit less than the forward speed the birds need to efficiently glide.

Gliders can do the same, but since they are bigger, they need a mountain range where the seagulls can do with a several feet embankment.


How is the cockpit rear view of an Airbus A340?

I Googled for "a340 360 cockpit view" that returns, with others, this link.

The link is a 360-degree view of the A340 cockpit. Below is a frame grab for one of the angles:


How do airports in hot climates handle extremely high temperatures?

Transport aircraft are certificated to a maximum operating temperature for departure that is related to International Standard Atmosphere (ISA), typically 35 deg C above ISA (there may be airplanes certified to ISA +40), ISA being 15C at sea level and dropping from there at the standard adiabatic lapse rate .

ISA temperature at Phoenix airport at 1135 ft ASL is about 13 deg C, so the max temperature you can operate at is 48C, if your plane is certified to ISA +35 (if your plane was certified to ISA +40, you'd be good to 53C).  This is based on the airport temperature reported on ATIS, not temperature measured at the aircraft.

At 48.9 C in the case you mentioned, you are above your maximum certified temperature for takeoff, so you are stuck until it cools off, and you'll simply have to wait for the temperature to drop a degree later in the day.  This applies anywhere in the world based on the ISA temperature for the airport. So for example at a Middle Eastern airport at sea level, where ISA is 15C, you'd be good up to 50 deg C, and if it's above that temperature, you wait for it to cool off.


Does a left spin differ from a right spin for a single-engine propeller aircraft, in terms of spin characteristics & ease of recovery?

Chipmunk, left-handed engine: Spinning to the left, recovery takes 3/4 turn, spinning to the right, recovery takes 1/4 turn. In either case, descent rate is 6000ft/min, so not affected by the airflow direction.


What's the meaning of "the break is a level" in a recovery operation of an aircraft carrier?

"Level" isn't a noun here--it's not that the break is a level.  Level is an adjective describing the kind of a turn.  A break is a turn; that turn is a level turn (neither descending nor ascending), and a 180 degree turn, and it is made at 800 feet.


Why not mount airliner jet engines above the wings?

Maintenance

Having the engines below the wing makes them fairly easy to access, even if some kind of lift is needed. Putting them above the wing would make them much harder to get to. Dropped a tool? Better start on that wing repair too. This includes both general access to the engine and the procedures for removing and installing the engine.

Structure

An engine below the wing is fairly stable, since it is hanging from above. It naturally wants to keep hanging downwards. Mounting the engine above the wing would be less stable. It naturally wants to tip over.

Noise

If an engine is under the wing, it helps to block some of the noise from at least the mid cabin. An engine above the wing would expose much more of the cabin to noise. It could reduce the ground noise while in flight, though.

Aerodynamics

The top of the wing is the most sensitive part aerodynamically. This is why items like fuel tank access panels are placed on the bottom. Having an engine and pylon on top would affect the flow over the top of the wing.

Safety

Engines falling off the wings tends to be a bad thing. But if they were above the wing, they would tend to fall down onto the wing, which would still not be good. It would be harder to have then break away in a crash. Also, in the event of an uncontained failure, the wing would not provide any protection to the fuselage.

Of course there are benefits, such as the reduced noise, less ground clearance required, no interference between the jet blast and the flaps, and less chance of FOD being ingested. As new engines get larger fan diameters, the constraints become more difficult. Some concepts of the blended wing body design put the engines on top of the body. But for the current design of aircraft, the benefits of having the engines below the wing are greater than those of the alternatives.


What changes were made to the 777 as a result of British Airways 38?

The aircraft accident was caused by ice accumulating in the Fuel Oil Heat Exchanger (FOHE) of the Rolls-Royce Trent 800 engines which subsequently blocked fuel flow to the engines. The official accident investigation concluded:

  The investigation identified the following probable causal factors that led to the fuel flow restrictions:

  Accreted ice from within the fuel system released, causing a restriction to the engine fuel flow at the face of the FOHE, on both of the engines.
  Ice had formed within the fuel system, from water that occurred naturally in the fuel, whilst the aircraft operated with low fuel flows over a long period and the localised fuel temperatures were in an area described as the ‘sticky range’.
  The FOHE, although compliant with the applicable certification requirements, was shown to be susceptible to restriction when presented with soft ice in a high concentration, with a fuel temperature that is below -10°C and a fuel flow above flight idle.
  Certification requirements, with which the aircraft and engine fuel systems had to comply, did not take account of this phenomenon as the risk was unrecognised at that time.

(official accident report summary)

(image source: official accident report)

The FAA issued an amendment to an older Airworthiness Directive (AD) in March 2009:

  Boeing Model 777-200 and -300 Series Airplanes Equipped With
  Rolls-Royce Model RB211-TRENT 800 Series Engines

  [...]

  SUMMARY: The FAA is superseding an existing airworthiness directive (AD) that applies to
  certain Boeing Model 777-200 and -300 series airplanes. The existing AD currently requires revising
  the airplane flight manual (AFM) to include in-flight procedures for pilots to follow in certain cold
  weather conditions and requires fuel circulation procedures on the ground when certain conditions
  exist. This new AD retains the fuel circulation procedures. This new AD also revises the AFM
  procedures required by the existing AD. This AD results from a report of a single-engine rollback as
  a result of ice blocking the fuel oil heat exchanger. We are issuing this AD to prevent ice from
  accumulating in the main tank fuel feed system, which, when released, could result in a restriction in
  the engine fuel system. Such a restriction could result in failure to achieve a commanded thrust, and
  consequent forced landing of the airplane.

(AD 2009-05-11)

The NTSB then requested a redesign of the FOHE from Rolls-Royce:

  The US National Transportation Safety Board (NTSB) on 11 March released urgent safety recommendations for the redesign by Rolls-Royce of the fuel-oil heat exchanger on Trent 800 engines powering Boeing 777s.

  NTSB says Rolls-Royce is already working on a redesign that could be available in twelve months, but still felt compelled outline the need for the heat exchanger overhaul.

(flightglobal.com)

In Europe, EASA required the new FOHE to be installed since January 2011 at the latest:

  Reason:

  This Airworthiness Directive has been raised following an incident involving dual
  loss of engine response in the final stages of approach leading to touchdown
  short of the runway. The phenomenon involved in the loss of engine response
  has also been seen in flight affecting just one engine.

  Post incident analysis and investigation has established that, under certain
  ambient conditions, ice can accumulate on the walls of the fuel pipes within the
  aircraft fuel system, which can then be released downstream when fuel flow
  demand is increased. This released ice can then collect on the FOHE front face
  and limit fuel flow through the FOHE. This type of icing event was previously
  unknown and creates ice concentrations in the fuel system beyond those
  specified in the certification requirements.

  To mitigate the risk of dual engine FOHE blockage within the Trent 800 engine
  powered Boeing 777 fleet, which constitutes a potential unsafe condition, this
  Airworthiness Directive instructs replacement of the FOHE with a modified
  standard incorporating enhanced anti-icing and de-icing performance.

  Required Action(s) and Compliance Time(s):

  Within 6 000 flight hours from 10 July 2009 or before 01 January 2011,
  whichever occurs first:

  Replace the FOHE with an FOHE modified in accordance with RollsRoyce Alert Service Bulletin RB211-79-AG257, dated 24 June 2009
  (published 10 July 2009).

(EASA AD 2009-0142)

Regarding your bonus question: Yes, there was another incident (Delta Air Lines Flight 18, 26 November 2008) where ice accumulation in the FOHE resulted in an engine rollback (luckily only one engine this time):

  Since we issued AD 2008-19-04, we received a report of a single-engine rollback as a result of
  ice blocking the fuel oil heat exchanger (FOHE) on a Model 777 airplane equipped with Rolls-Royce
  Model RB211-TRENT 800 series engines. The data confirm that ice accumulates in the fuel feed
  system and releases after a high thrust command, creating blockage at the FOHE and resulting in the
  inability of the engine to achieve the commanded thrust. Examination of the data from the rollback
  shows that the second of two maximum thrust step climbs was performed approximately 40 minutes
  prior to the thrust rollback. Ice was released within the fuel system during the step climbs and formed
  a restriction at the FOHE of the affected engine, as evidenced by an increase in engine oil
  temperature.

(AD 2009-05-11)


How is a traffic pattern oriented, entered and exited?

The instruction to join a "left downwind" is used to clear an aircraft into a standard traffic pattern with lefthand turns. The word "left" could be omitted, as only right turns and righthand traffic patterns are called with "right". In the case of EGLL - London Heathrow the standard pattern would be a northern traffic pattern for runways 09L/09R and a southern traffic pattern for runway 27L/27R.

If you should come to the unlikely situation that you are VFR and want to depart from Heathrow, the clearance to leave the CTR in a northerly direction would be best executed leaving the crosswind, but clarification on frequency never killed anybody:

A: Heathrow Tower, G-ABCD, request leave CTR direct northbound after crosswind 09L.

or

A: Heathrow Tower, G-ABCD, request heading 360 after turning crosswind 09L.

When departing an aerodrome with traffic, it is unwise to leave the CTR along the extended centerline/upwind, as you are impeding other traffic, especially in slower aircraft.


Why are critical flight computers redundant?

Failure modes to consider:

Overheating. This changes the chip's timing properties and eventually results in error. This can manifest as single-bit errors in the middle of seemingly normal operation; it will eventually crash, but may output bad data first.
Water damage. Manifests as a parasitic resistance on the board and may cause you to misinterpret bits as high or low. May be leaky housings, condensation, etc.
Electromagnetic interference. (The system is supposed to be resistant to this, but it's still worth thinking about).
Physical connection problems. Either during construction (soldering faults) or induced afterwards (heat, vibration). Microscopic cracks in boards or joints can pass QA but result in intermittent faults. Again this can lose you a single bit at a time. This is related to the Xbox "red ring of death" issue.
Failure of other components. Capacitors are the usual suspect; electrolytic, tantalum, ceramic all have different failure modes. Again this may result in a system that mostly works but is prone to misinterpreting marginal values or suffers from timing drift.
Weird materials science ("Purple plague", tin whiskers due to lead-free solder)
Part QA may not be up to the standards you expect (suppliers shipping inferior parts with a bogus "aerospace grade" label). Hard to detect even after it's happened.

It's important to recognize that in high-speed digital systems you don't get nice clean "one" and "zero", you get a series of rising and falling edges that are smeared out by the parasitic capacitance and inductance of the wiring. This is inherently vulnerable to being misinterpreted in marginal electrical conditions.


I do not know the exact numbers for oleo stroke and so on, but this is how you would calculate this. A 747-400 weighs 400 tons on take-off and 296 tons on landing, maximum. See here for the source of those figures.

Next is the landing speed, this is approx. 160 knots = 82 m/s. Now let's assume the pilot has misjudged the height and does not flare, but slams the aircraft with the 3° approach angle into the runway. It is supposed to survive this, so let's just continue. This gives you a vertical speed of 4.3 m/s, and at 296 tons this is an energy of 2,750 kWs = 0.76 kWh, which needs to be dissipated by the landing gear. Now I make the assumption that the gear stroke is 0.5 m (those who know please put it in the comments, and I will correct the calculation). We have 0.5 m to decelerate a mass of 296 tons from 4.3 m/s to zero. If we assume a constant deceleration, the force will also be constant and the sink speed will decrease linearly.

The average sink speed during this process is 2.15 m/s, so it will take 0.23 s and an acceleration of 18.5 m/s$^2$. Force is mass times acceleration, so the force is 5,473 kN or 1.23 million pounds. This is just the inertial force to stop the descent. While taxiing to the take-off position, the aircraft will press with 400 tons = 878,000 lbs on the runway, since the wings do not yet produce any lift. This shows that even a hard landing does not stress the landing gear so much - after all, the acceleration is just shy of 2 g, acting on a much lighter plane.

In reality, the landing gear of a 747 is staggered, so the inner main gears will touch the ground first. Also, I expect that the force will not be constant along the whole gear stroke. This will change the details of this approximation, but the general magnitude should not be different.

This answer goes into more details on how to calculate the damage an airplane will do to a given runway or apron.

Now for the braking stresses. The landing field length of a 747-400 is 2175 m, and let's just assume that the pilot forgot to use thrust reversers, aerodynamic drag was switched off that day, and all the braking power had to be supplied by the 16 main wheels. Let's also assume that the pilot uses 1200 m of that field length for braking (I'm just making this up to get to an upper limit of what force will act on the tarmac). Now we need to decelerate from 82 m/s to zero within 1200 m. Linear deceleration means an average speed of 41 m/s, so the whole process takes 29.27 s. Dividing speed by time yields a deceleration of 2.8 m/s$^2$.

To bring the aircraft to a full stop, we have an energy of 995,152 kWs = 276.4 kWh to dissipate along a distance of 1200 m. Using again Newton's second law, we see that this requires a horizontal force of 829 kN = 186,322 lbs, which translates into 51,8 kN = 11,645 lbs per wheel. This is certainly more than what happens in reality, but to put it into proportion: The static load per main wheel at the maximum landing mass is 174 kN = 39,150 lbs (assuming that 4% of the mass is carried by the nose gear). This extreme (horizontal) braking force is still less than 30% of the (vertical) static load, which is well below of the maximum braking coefficient of an aircraft wheel on a dry runway.

EDIT:
CGCampell correctly remarked that emergency procedures at take-off weight will produce the biggest braking loads. Now I will calculate the highest possible braking loads, and for this I need this plot of a polynominal for the braking coefficient, which is the ratio between vertical and horizontal forces before the tire skids. I do not know the source; I collected it somewhere in the past and never found a reason to doubt its validity.

Shortly before the aircraft comes to a stop, the highest friction coefficient is reached, and then little lift is produced by the wings, so the vertical tire loads are those of the static case. At 96% of 400 tons acting on 16 wheels, this is 24 tons = 235,344 N = 52,907 lbs of downward force per wheel. Since the friction coefficient is 1 at low speed, the same load is transferred horizontally from each wheel to the ground, almost five times more than what I approximated for the landing above. Clearly, going to the limits produces much higher loads.

Formulas used in the calculation:

How to calculate the deceleration of a mass $m$ from a speed $v_0$ to $v_1$

Energy has no absolute value, we just add or subtract energy. The amount of energy change $∆E$ between the aircraft at a speed $v_0$ and at a speed $v_1$ is:
$$∆E = \frac{m}{2}\cdot (v_0^2 - v_1^2)$$

The unit of energy is the Joule, which equals the Watt-second or the Newton-meter. Thus 1 J = 1 Ws = 1 Nm = 1 $\frac{\text{kg}\cdot \text{m}^2}{\text{s}^2}$. Metric units are neat, right?

In physics, energy $E$ equals work $W$, and work is performed when a force $F$ travels along a distance $s$. As does the braking force, acting on the moving aircraft:
$$E = W = F_{brake}\cdot s$$

How do we get the rollout distance $s$?

We use the fact that the energy change due to deceleration equals the brake energy:
$$\frac{m}{2}\cdot (v_0^2 - v_1^2) = F_{brake}\cdot s \Leftrightarrow s =  \frac{m}{2\cdot F_{brake}}\cdot (v_0^2 - v_1^2)$$

How can we find the time $t$ it takes to slow the aircraft down?

If the force is constant, the acceleration $a = \frac{m}{F}$ is constant, too. So the speed over time $v(t)$ is:
$$v(t) = v_0 + a\cdot t$$

We decelerate, so $a$ is a negative number. But the same works for a positive acceleration, too. To find the time $∆t = t_1 - t_0$ we make use of the fact that v varies linearly over time, such that the average speed is the arithmetic mean between $v_0$ and $v_1$. And time is just distance divided by speed:
$$∆t = \frac{2\cdot s}{v_0 + v_1} = \frac{m\cdot s}{F_{brake}\cdot(v_0 + v_1)}\cdot (v_0^2 - v_1^2)$$

With such formulas it is always a good idea to compare the units on both sides. Yup, seconds, so the result is really a time.


Why is AVGAS so much more expensive than car gas?

The LL of 100LL stands for Low Lead as it has tetra-ethyl lead added as a detonation inhibitor for high-performance engines. Despite the "low" moniker there actually is a lot of it in there, and it's toxic. This fuel is expensive for a number of reasons:

The lead itself is expensive
The lead additive means that a refinery must shut down and clean the lead before producing other fuels, this means more refinery time and therefore more costs
Lead in fuel cannot be allowed to contaminate other fuels so you cannot pipeline leaded fuel. It has to be transported in containers, adding to shipping costs
There are extra controls around the lead in many parts of the world, namely storage requirements and paperwork, all which costs
100LL fuel has many more "aromatic" hydrocarbons than mogas (auto fuel) in order to increase the octane levels and prevent fuel from vaporizing in your lines at high altitude. It's much higher grade, so it costs more
It's a specialist fuel made in much less quantities than other fuels, so a premium is added to ensure a profit

Keep in mind that the Avgas is taxed less than Mogas in most places. It would cost even more if it were taxed the same!

Efforts are underway to come up with a 100LL replacement that will work the same in all engines and situations, which is a hard problem to solve. Whatever fuel they come up with, while having no lead, will still likely be more expensive than mogas just because of the more expensive hydrocarbon mix and the specialist nature of the fuel.


What does it mean when an aircraft engine is de-paired?

De-pairing means literally braking up pairs. In the case in question, it means that if an aircraft is equipped with engines of a certain specific type, one of the engines has to be replaced with a version that has been upgraded.

The reason for the de-pairing is to mitigate the risk of a dual engine failure: Having two engines that are both affected by the same issue considerably increases the risk of both engines failing on the same flight. At least RR Trent 1000 and P&W 1100G have been issued a de-pairing AD by EASA.

Article on RR Trent 1000 de-pairing AD on Airlineratings.com

Article on P&W 1100G de-pairing AD on samchui.com


What is the device at the tail of the F-16 Block 60?

That’s a ram air intake and exhaust for a heat exchanger used to cool the Falcon Edge Integrated Electronics Warfare Suite (IEWS). The system remains fairly clandestine, but a few of its components are known to exist.

https://www.northropgrumman.com/Capabilities/FalconEdgeIEWS/Pages/default.aspx


Can a pilot amend a flight plan in-flight?

Anything and everything (well, maybe not the aircraft type...). A flightplan is just that - a plan. The pilot's intentions can change during flight for any number of reasons. Just inform ATC of your new intentions, request a new clearance as appropriate, and ATC will accommodate the request if possible. Happens all the time.


Do jets breaking the sound barrier leave shredded metal on the ground?

I don't think this had anything to do with military jets breaking the sound barrier nearby; it does sound more like strips of metal recovered from chaff dispensers on the jets; countermeasures systems which eject hundreds of strips or threads made of metal foil used to thwart enemy radars.  Most likely the aircraft discharged their chaff dispensers during training exercises over the farm; you simply recovered some of the metal strips.

Wikipedia

Source


Which aircraft require that the vertical position of the centre of gravity is checked?

In many aircraft the vertical (Z axis) placement is of little impact on weight distribution.  However, in some aircraft it affects maneuverability.  So for an aircraft like a C-5 it is noticeable, yet a C-5 is not considered an aircraft where vertical CG would be a factor, as the nature of the operations are, well, cargo hauling.  In a helicopter, which tends to have a higher (Z-axis) CG with the top placement of the engine and transmission, the considerations are greater. It doesn't impact loading in a normal sense, but there is a noticeable impact in handling particularly when roll moments are involved.

Stated perhaps more simply, static stability is normally bounded by longitudinal and to a lesser degree latitudinal forces. However, a higher CG will impact dynamic stability where the consideration is not primarily limited to wing (rotor) and airfoil loading.

So the simplest answer is that it does make a difference, which is more than just measurable in some applications, but normally the difference is of small consequence and only a tertiary consideration.


Why is the compressed air (from engine compressors) taken from High Pressure (HP) stage instead of Low Pressure (LP) stage?

Coming from the compressor section of the engine, the bleed air is sent to the precooler. Even air from the "low" pressure section needs to be cooled before it is sent to the air conditioning system. Here is a precooler from a CitationJet:

The page with that image notes that the bleed air is "hot enough to melt insulation and alter the heat treatment on aluminum alloys." The precooler reduces the temperature of this air and regulates the pressure to the pack system.

When the engine is at low power settings, bleed air is taken from the high pressure section. The engine must run fast enough that this provides enough pressure for the bleed system to operate properly.

Once the engine gets to a higher power setting, the bleed air is taken from the low pressure section. At higher engine speeds, this air still has the pressure required to run the bleed system.

Since the bleed system needs a minimum pressure to operate, compressing the ambient air to this pressure will always add a certain amount of heat.

Here is a diagram of the bleed system, to help visualize what is going on. Note that even after the air goes through the precooler, it is still hot enough to be used for wing anti-ice.


If the pilot reduces the airspeed while he increases the rate of descent, you will not notice any change in pitch attitude when the aircraft descends. With jets you should be able to hear a change in engine pitch when thrust is reduced. Turboprops run their engines at constant speed, and a reduction in power here means a reduction in propeller pitch. This causes the propeller noise to change, but this change is harder to discern. With a little practice you should be able to hear the slight drop in propeller noise which signals the begin of the descent, though.

Gliders control their sink rate by flying in rising or sinking air, and additionally by flying slow (and near their minimum sink rate) or fast. To descend quickly, they can open speed brakes and/or sideslip. My favorite for a fast descent is to spin the aircraft, but airliners do not use this option.

In order to produce the necessary lift to keep the aircraft in the air, the pilot picks a combination of speed and angle of attack at which lift equals weight. Other combinations would result in an accelerating vertical speed and are only used in transitions from one flight state to the next.

To arrive at the aircraft's pitch attitude, you need to add the flight path angle to this angle of attack. If the plane descends with a flight path angle of -3° and the pilot reduces speed such that he needs to increase the angle of attack by the same 3° to produce the same lift, the resulting pitch angle of the aircraft would stay the same.

Normally, the correct answer to your question is 2. Reduction of engine power. But the other answers are also correct: If the speed is held constant, the attitude has to be reduced by the desired flight path angle change. Note that this is achieved by reducing thrust alone. If the pilot wishes to descend really fast, he might move to answer 3. Combination of both as in this answer.


Where can fuel consumption data by aircraft type and route be found?

I am providing an answer to my own question. However, hopefully, someone will be able to expand further on this.

For US Airlines, the bureau of transportation statistics is a reliable source. And the data is free!


What is this small number on the top right of an IAP?

It is the year followed by the day of the year of the last ammendment to the chart. If there have been no changes to the chart since it was first issued, this space is blank. In this case the chart was revised on the 171st day of 2019. If you look at the bottom left hand portion of the chart, the date shows the last time the procedure was revised e.g.—17AUG17. Apparently there were changes to the chart (obstacles,  name of the airport, typos in the notes, etc.) that did not affect the procedure, so the dates are different.

Refer to the Aviation Chart User’s Guide.

  The Date of Latest Revision is shown on the top margin above the
  procedure title. The Date of Latest Revision identifies the Julian
  date the chart was last revised for any reason. The first two digits
  indicate the year, the last three digits indicate the day of the year
  (001 to 365/6).

  The FAA Procedure Amendment Number, located on the left bottom margin
  below the City, State, represents the most current amendment of a
  given procedure. The Procedure Amendment Effective Date represents the
  AIRAC cycle date on which the procedure amendment was incorporated
  into the chart. Updates to the amendment number and effective date
  represent procedural/criteria revisions to the charted procedure,
  e.g., course, fix, altitude, minima, etc.


Do captains and first officers always fly together or are they mixed?

In airlines where pilots bid on monthly lines it is conceivable that a pair of pilots fly all month together. However, trip trading and reassignments rarely let this happen. It is far more common that a crew only stays together for a single "pairing" that lasts between 1 and 4 days (domestic 121 USA).

It's not a drawback to fly with new people because training emphasizes standard flying according to the FOM. Ideally, every pilot is exactly the same.
  Practically it is close enough that you can drop any two pilots from the same airline into an airplane and they more or less operate it exactly the same way.


Why does a steeper approach cause an increased landing rollout?

I'll just formalize my comment here as an answer:

Landing is all about managing the aircraft's energy. When you are coming in for a landing with a steep approach it usually means that you will have more energy (speed) as you approach the ground. A high ground speed as you approach the runway usually means floating and/or, just like in a car, a longer distance to slow down. That extended distance you would need to bring the plane to a stop or slow enough to taxi off the runway would be the extended roll-out. Therefore B is the best answer.

A is incorrect because a steep approach does not necessarily mean a hard landing. The smoothness of a landing is dependent on the pilot knowing the appropriate moment to flare.

C is incorrect because unless the pilot is trying to land short of the threshold a steep approach can be done anywhere over any part of the runway/approach.


Instructor can't talk when H10-13.4 is plugged in

So after Juan's help and also talking to Becker I think I've found the answer:

It's an unlucky impedance combination.

That means maybe I can get it to work by lowering the VOX-level (increase mic bias) far enough so my instructor can activate it but if I lower it too much, my own mic will constantly activate the intercom, resulting in constant noise.

Becker told me, this is likely due to an old wiring version being installed where both pilot and copilot's mic are connected in parallel to the same amplifier. So when my mic has a 'better efficiency' i.e. better conversion from mechanical swing to voltage, the VOX adapts the threshold (or as Becker said the bias voltage for the mic) for this and the amplitude of the co's mic is to low to activate it.
A fix would at least require rewiring of the system to have dedicated amplifiers and bias supplies for both the pilot and co-pilot.

I think I confused some things in the physics here; if you point me to it, I will gladly correct it.

In general Becker's advise was to always use the same kind of headset for both pilot and all passengers in order to ensure best results (all volumes will be the same for all people then).


Is it normal to take off with limited flaps on a B737?

That looks like Flaps 1, and that is not only normal and safe, it is very common on relatively long runways (7500' and longer). For slightly shorter runways, a Flaps 5 takeoff is often used, and for the shortest runways (less than 5500', roughly), even Flaps 15 or on some aircraft, Flaps 25.

All of those are entirely safe options.

As the runway gets shorter, you get the best performance -- defined as how much weight you can carry while still meeting all requirements -- with an earlier liftoff. This means, more flaps to enable rotating at a slower speed. The downside of more flaps is more drag, which reduces initial climb performance. To get the most weight possible, you'd use an extremely long runway, a high takeoff speed, and minimal flaps (i.e. Flaps 1 as you had) for the best performance in the climb. But when the runway isn't so long, you start to be more limited in the weight you can carry, and to get the best results, more & more flaps become optimal as the runway gets shorter.

It sounds like your flight was probably pretty heavy -- a full -800 certainly would qualify -- and so the crew took advantage of the long runway to accelerate to a fast takeoff speed using Flaps 1. In the air, the aircraft will fly fine at that weight, but it isn't as nimble and won't accelerate as quickly as a lighter 737 would. If you're used to the performance of a 737 loaded with the fuel for a one or two hour flight, it isn't surprising that the aircraft with enough fuel for a 6 hour flight (plus reserves, in both cases) would seem sluggish in comparison.


Aircraft design has not changed that much in the last 10 years. In fact, most aircraft in production 10 years ago are still in production.

The cargo holds in typical airliners are indeed pressurized. Take a look at a cross section of an airliner (A380 here):

The round shape of the fuselage outline is very efficient at withstanding pressure. Because of that, everything within the fuselage shape is pressurized. This includes the cargo hold below. Only cargo holds located behind the aft pressure bulkhead would be unpressurized, and these are mainly found in smaller aircraft.

The floor of the passenger cabin is not designed to withstand that pressure, because the flat surface would need to be much heavier to do so. Decompression events are considered by regulations though, so there are vents that allow the pressure to equalize. In older aircraft without these vents, a decompression event can cause the floor of the cabin to collapse, as in this incident (and because it wasn't addressed, this one too).

  Are cargo holds heated?

Sometimes. This will depend on the aircraft type. There are many threads over on the TechOps forums about this. The temperature can be adjusted depending on the cargo load.

Although the air outside the plane is cold, the walls are insulated (also for fire protection), and being pressurized along with the cabin helps too. Even in unheated cargo holds, the temperature should be above freezing. For example, the cargo bay of a 767 stays above 7˚C but with heat stays above 18˚C.

  Do they have lights? (Aren't some lit for animals?)

They do have lights, mainly for ground crew during loading and unloading. See this Boeing page about fire protection where it mentions that "another safety feature on many newer airplane models prevents the cargo lights from operating in flight".

  and what about Fedex-type cargo-only aircraft?

These aircraft are still based on the airliner models (and sometimes converted from airliners). Therefore, they have the same pressurization system. The cabin is still pressurized, or they would have to put in some type of bulkhead behind the cockpit.

This includes the cargo version of the 747 (both upper and lower areas are pressurized).

The rare exception would be aircraft like the 747 LCF (Dreamlifter). The cargo section is not pressurized, and there is a bulkhead behind the flight deck section.


What exactly did this mechanic sabotage on the American Airlines 737, and how dangerous was it?

It's a serious crime, but what that guy did, only affecting one system out of three, would be unlikely to cause a crash if the pilots were half way reasonably competent.  The take-off would be rejected as soon as the blocked side's speed tape failed to "come alive", well below 80kt (the pilot not flying checks that both speed tapes start to move as the airplane accelerates - this would be the first obvious clue and is a very basic action on a jet).


Does a stopper (chock) really prevent the plane from moving?

Wheel chocks are used to prevent accidental movement, generally on airplanes. They are placed in addition to setting the brakes, if present.

On smaller planes, chocks are used to prevent the airplane to roll, and tie downs are used to prevent the airplane to stay on the ground and not take off on its own. Using both the chocks and tie downs will ensure that airplane is secured and will not move, under normal conditions of course. Other safety measures are discussed in this answer.


What are the reasons behind this pusher propeller configuration?

Yeah good question. They need it to be out of the way of the spray, so high up, and they position it on top of something that looks like a vertical stabiliser, so why not use the vertical stabiliser, I presume is what you mean. Like this one, but then in a pusher comfiguration

My answer would be that that would position the centre of gravity too far back. The engine is heavy, it's best if it is mounted close to the centre of the plane. The combination of pusher prop and tail mounting would make for a configuration that wants to tip backwards. Placing the wings further back is awkward, it's a small plane and leaves little moment arm for the tail surfaces to work effectively.


Can a UAV over 55lbs legally fly 20 miles off the US coast?

The United States does not own or control airspace outside its territorial limits, but there is an exception; our government has extended Class A airspace out to twelve miles from the coast of the contiguous 48 states and Alaska. If you launch the UAV at sea and stay out of US airspace, there's no need to ask for an exemption.


How do combat jets know when to launch flares to counter IR missiles?

Actually most aircraft don't actively know when a missile is being fired at them. I have worked on helicopters and fighters that deploy counter measures.

The first is an IR jammer which we call a disco ball. It is made up of mirrors at different angles that resemble a disco ball. It radiates an IR signal at different angles to confuse the missiles.

The flares or chaff are fired periodically in known hot spots. This creates heat signatures similar to the engines and confuses the missiles.

There are active systems but they don't work well. I have seen a helicopter in testing suspended from a wire with countermeasures turned on. A missile was fired and the countermeasures didn't even get deployed. This is why they usually keep firing the flares or chaff in known hot spots.

Hope that helps.


What would it take to have a new large civil aircraft manufacturer?

What are the chances a start-up, with no state money, will come to market with a new 100+ seats plane in the next 20-30 years?

If you count Bombardier, the chances are roughly 100%. The Bombardier C-Series, which will seat 140 (160 max,) is scheduled to enter service within this year (2015.) However, Bombardier is hardly a 'start-up' in the normal sense.

Bombardier C-Series Mock-Up (Source: Wikipedia)

For a real start-up (e.g. a SpaceX-style company,) the chances will be much more slim. It takes billions of dollars worth of investments to design a modern commercial airliner before you will ever see the first dime of revenue. Start-ups generally won't have access to that kind of money until they have had time to mature and developed a steady revenue stream from other successful products (which is how Bombardier is doing it.)

  Could a SpaceX type of company be successful in the airplane manufacturing industry?

That depends greatly on the type of airplanes in question. Undoubtedly, this is possible in the light general aviation market. Several such companies have come and gone over the years. One interesting start-up that is planning to enter production soon is Terrafugia, a start-up from MIT, which is building aircraft that fold up into street-legal cars that can just drive away from the airport and park in your garage. However, the larger airliner market is a completely different ballgame, involving development costs that are orders of magnitude higher. Start-ups have a difficult time getting started in markets with such huge barriers to entry.


Why do we need a negative derivative of the pitching moment? restoring moment should be enough?

So let’s assume the aircraft has a $C_{m_a}$ curve as you show. When you start to pull up you will feel nose down force on the yoke because of negative pitching moment. As you further increase the pull, the force required should increase also. However in your picture at some point the negative pitching moment $C_m$ decreases (in magnitude), still negative though. That can cause all unwanted motions in the aircraft because suddenly the force you are applying is becoming too excessive. It can even over-g the aircraft depending on the conditions. You are basically braking the linear response of the aircraft.
Ironically enough , that was the main reason Boeing 737 Max was equipped with MCAS in the first place. The stick force per g was not linear at some corners of the envelope. So they put MCAS to linearize the $C_{m_a}$, initially. Of course then they extend it to low speed region also.
Additionally, Part 25 Airworthiness Standards for big aircrafts requires stick force curve slope to have a stable slope:

§25.175   Demonstration of static longitudinal stability.
…
(1) With the landing gear retracted at high speed, the stick force curve must have a stable slope at all speeds within a range which is the greater of 15 percent of the trim speed plus the resulting free return speed range, or 50 knots plus the resulting free return speed range, above and below the trim speed (except that the speed range need not include speeds less than 1.3 $V_{SR1}$, nor speeds greater than $V_{FC}$ / $M_{FC}$, nor speeds that require a stick force of more than 50 pounds), with—

As for the small aircrafts the Part 23 requirement has a little bit of a leeway:

§23.2145   Stability.
(a) Airplanes not certified for aerobatics must—
…..
(3) Provide stable control force feedback throughout the operating envelope.

The part you are asking is specifically addressed in FAA AC25-7C:

§26
...
There may be no force reversal at any speed that can be obtained, except lower than the minimum for steady, unstalled flight or, higher than the landing gear or wing flap operating limit speed or VFC/MFC, whichever is appropriate for the test configuration.
...
(4) Examples of “local reversals” are given in Figure 26-2. Curves A and C depict a local gradient reversal within the required speed range. Even though it might be argued that the “average gradient” meets the one pound in six knots criterion, the gradient reversals would render these characteristics unacceptable. Curve B depicts a situation in which the gradient reverses, but only outside the required speed range. In addition, Curve B demonstrates a situation in which the local gradient does not always meet the required one pound in six knots, even though the average gradient does.


Is a stall warning horn required to fly?

No, many aircraft don't have them, like the Cherokee since it uses a gear warning horn. The horn signifies that the gear isn't down and you don't want to confuse that with the stall warning, so they don't have one.

23.207 says that an audible or visual indication is not required as long as the aircraft exhibits a "warning" 5 knots before the stall, in the case of the Piper Comanche the warning that satisfies the requirement is the stall buffet.

The relevant section of 23.207 is part (b):

  (b) The stall warning may be furnished either through the inherent aerodynamic qualities of the airplane or by a device that will give clearly distinguishable indications under expected conditions of flight. However, a visual stall warning device that requires the attention of the crew within the cockpit is not acceptable by itself.

So the stall buffet, as long as it is pronounced, is adequate indication of a stall to satisfy 23.207.


What is the difference between 'warning area' and 'ADIZ'? Are they overlapped with each other?

You can find a good explanation of Warning areas (and lots of other areas) in the answer to this question.

ADIZ is effectively the controlled area that surrounds the US/CANADA border. The picture from the wiki article shows it quite well

The ADIZ was created to have an area to identify inbound, out of country, aircraft. As per the FAA

  All aircraft entering U.S. domestic airspace from points outside must
  provide for identification prior to entry or exit. ADIZs have been
  established to assist in early identification of aircraft in the
  vicinity of international U.S. airspace boundaries (AIM Section 6,
  5-6-1)

As far as I know there are no ADIZ areas internal to the country, although warning areas may be anywhere within the nations jurisdiction. I see no reason they could not overlap each other either.


Are jet engines affected by small bird (e.g. hummingbird) strikes?

All turbine engines must pass a series of tests, including water ingestion (flying through clouds) and bird strikes. For bird strikes, the following article does a good job explaining the requirements to pass bird strike testing:
Aircraft Certification for Bird Strike Risk

It cites 14 CFR Part 33-77 'Foreign object ingestion - ice' (although 14 CFR Part 33-76 'Bird ingestion' seems more appropriate) and EASA Airworthiness Code CS-E 800 'Bird Strike and Ingestion' as sources.

14 CFR Part 33-76:

  (4) A small bird ingestion test is not required if the prescribed number of medium birds pass into the engine rotor blades during the medium bird test.

  (5) Small bird ingestion tests shall be conducted so as to simulate a flock encounter using one 85 gram (0.187 lb.) bird for each 0.032 square-meter (49.6 square-inches) of inlet area, or fraction thereof, up to a maximum of 16 birds. The birds will be aimed so as to account for any critical exposed locations on the first stage rotor blades, with any remaining birds evenly distributed over the engine face area.

  (6) Ingestion of small and medium birds tested under the conditions prescribed in this paragraph may not cause any of the following:

  More than a sustained 25-percent power or thrust loss;

  The engine to be shut down during the required run-on demonstration prescribed in paragraphs (c)(7) or (c)(8) of this section;
  The conditions defined in paragraph (b)(3) of this section.
  Unacceptable deterioration of engine handling characteristics

EASA Airworthiness Code CS-E 800

  (d) Medium and small birds ingestion tests. Engine ingestion tests and analysis with medium and small sized birds must be carried out as specified below. Alternative evidence may be acceptable as provided under CS-E 800 (f)(1). The small birds test will not be required if the prescribed number of medium birds pass into the Engine rotor blades during the medium bird test.

  (B) Small birds. One 85 g bird for each 0·032 m2 of the inlet throat area or fraction thereof with a maximum of 16 birds, distributed to take account of any critical exposed

For more information, refer to 14 CFR Part 33-76, and EASA Airworthiness code CS-E 800.

One more thing to add - the documents do not include any tests for single small birds, only flocking small birds, and use birds that weigh 85 grams. Humming birds do not flock, and 85g is more than most humming birds weigh. That being said, the tests do include much larger birds, and all commercial jet engines found on commercial airlines certify large bird strikes, so it's likely that tests with small bird strikes are not conducted. Bouncing off of physics - if a turbine can withstand a large bird strike, it won't even feel a humming bird strike, therefore it is not a required test if the engine already certified with large bird strikes.


How to find trim condition of a sectional airfoil without knowing the angle of attack?

If you have access to a model of your airfoil, a moment balance, and a wind tunnel, you may determine $C_{M_{ac}}$ experimentally: the moment the wing experience may be normalized to calculate $C_{M_{ac}}$

Then solving for alpha is trivial. Otherwise a tool like XFLR5 may be useful to find  $C_{M_{ac}}$ for your airfoil.


What are the requirements for aircraft marker cones?

According to IATA Airport Handling Manual, safety cones should

be conical in shape
be of a minimum height of 750 mm (22.2″)
have a minimum base weight of 4.53 kg (10 lbs)
be orange in color with reflective striping.