What are the differences between symmetrical and cambered airfoils? I have seen images of cambered and symmetrical wings but apart from that what are the major differences between them?
I have also read that symmetric wings don't produce any lift at 0° AOA whereas cambered wings do.

Also, are the 2 statements given below true?

In a cambered airfoil, the aerodynamic center and center of pressure are not at the same place, so the lift created also generates a moment at the aerodynamic center.
In a symmetric airfoil, the aerodynamic center and the center of pressure are at the same place, so you do not have a pitching moment.

symmetric wings don't produce any lift at 0° AOA whereas cambered wings do.

Yes, that's correct.

Usually, the most important difference is that a cambered wing is optimised for a positive angle of attack. It produces less drag for the same amount of lift, and can produce more lift before stalling.

Obviously that assumes that the wing is the right way up - a cambered wing will be less efficient and stall earlier when inverted. And a symmetrical airfoil will produce less drag when no lift is required (e.g. a vertical stabiliser in steady flight)


Which fonts were used in old (1930s) aircraft cockpit displays and instruments? This is probably more of a graphic design question than aviation but maybe a few hangar rats around here know the answer.

What type fonts were used on the old instruments in aircraft from the 1930s like Lockheed Vegas, Electras, Beech Staggerwings, DC-3s, etc.?  I need it for a web site I’m working on.

I've seen a few times that even hand-written markings were used. This suggests that there hardly was any consistency.

  Photo from Darwin Aviation Museum:


What would be a safe minimum vertical separation distance between passenger-carrying multicopter aircraft? There is increasing talk about employing passenger-carrying multicopters ("taxi drones") to extend urban mobility into the third dimension. These aircraft will have MTOMs in the range of several hundred kgs.

In case this catches on on a larger scale, airspace use will increase considerably compared to the current occasional helicopter and sight-seeing flight.

For safety reasons, presumably a certain minimum vertical separation will be required due to the downwash from the rotors.

Is there any information available about the current thinking on required minimum vertical separation between manned/passenger-carrying multicopters? Also, will there be any difference for this requirement between hovering and cruise flight modes?

The downwash is directly related to total lift; more rotors just means each rotor is producing a smaller fraction of the total, and the end result should be no different for separation purposes than for one or two rotors.

There are a lot of obstacles to mass adoption of personal aircraft, but the exact lift mechanism is arguably the smallest.


How is an on ground lightning strike test conducted? Whenever a design company is obtaining an STC for an aircraft (Supplemental Design Certificate) for an electrical installation, one of the required tests to obtain the STC is a lightning strike test. The test is needed to show that the electronics installed can withstand a lightning strike without degrading their performance or inducing degradations into other systems.

We can't position the aircraft on ground waiting for a lightning bolt to hit like 'Doc' in 'Back to the Future', so how do design companies, or engine manufacturers, etc. simulate a lightning strike and draw conclusive results that the system with withstand actual lightning?

You create your own lightning. You can do that with an impulse generator. Here's what a smaller one looks like:

I don't know if that's what is used for the certificates but it certainly one way to test against lightning strikes (provided that you can generate a high enough voltage).


What are the main differences between scimitar and regular propellers? I am looking to know the main differences between scimitar and regular propellers. Can somebody help me on this?

Primarily the curved sweep of the blade's leading edge, allowing for better efficiency at higher engine speeds.


If DME is required, why have non-DME minima? I was looking at the ILS or LOC RWY 9 at KJZI today and I noticed that it had lower minima for when you can identify an intermediate fix (YOCUB).  That made sense, but the entire approach requires DME.  So, if that's the case, why even bother having non-DME minima?

Both of the missed approaches require DME.  Under what circumstance could you shoot this approach but your MDA would be 520?

Here's the current plate: http://155.178.201.160/d-tpp/1609/05354IL9.PDF

Conceivably the I-ETI DME transponder could be out of service, preventing you from identifying YOCUB (unless you have a second VOR or GPS), but you could still identify BASSO on the CHS DME for the missed.


What radial is the aircraft crossing? I'm working through the ASA Private Pilot 2020 Test Prep questions and there's a question I don't understand the answer for.

3579 (Refer to Figure 28, illustration 5) The VOR receiver has the
indication shown. What radial is the aircraft crossing?

A - 030
B - 210
C - 300

I thought the answer was B - 210 but that is the heading, not the crossing.
The correct answer is A - 030, but I'm not sure why. What does it mean to be crossing a radial?

A radial is always pointing (radiating) away from the VOR. But your instrument shows the TO/FROM indicator as TO. So you are crossing a 210 course towards the VOR, which means you are on the 030 radial from the VOR.

What does it mean to be crossing a radial?

This just refers to the fact that you cannot determine your heading (or track) from the CDI. Based on this instrument alone, you could be following the track to VOR right now or just happen to cross the radial at this moment (but actually fly in a totally different direction).


What materials are used in a Rolls-Royce RB211-524 Engine? I am trying to know what materials (Specifically metals) are used in making a Rolls-Royce RB211-524 Engine. I already found what is used in engines in general, but is it the same for all? And if so, what could be different in this specific engine?

Thanks!

There is some variation. The RB211 was to be one of the first engines to use a fan stage made in carbon fiber (Hyfil), but that plan was changed in a late stadium and the fan stage was done in titanium instead.  Conways did use Hyfil, IIRC.
Otherwise it's mostly steel and aluminium, with some titanium. Copper for the wiring etc.


How will a variable pitch propeller move during takeoff? In my ATPL books i've learned that for a variable pitch propeller, it is better to have a fine pitch for take-off (higher RPM) and a coarse pitch for cruise (lower RPM).

In this question taken from the ATPL question bank it states that a propeller will move towards the coarse pitch on take off.

Does anybody understand why the correct answer for this question is coarse pitch. Is this implying that we initially start our take-off with a fine pitch but slowly change towards a coarse pitch during the climb?

What happens is the prop at idle will be at the maximum fine pitch limit.  The prop control is set to Max RPM for take-off (it uses variation in pitch to regulate RPM) so the prop governor is set up to regulate engine rpm at redline once there is sufficient power to spin it that fast.

You add throttle to take off.  The engine increases in speed, with the prop blades still in full fine pitch, until it gets to redline RPM, which is also the governor setting.  When the RPM gets there, the governor now acts to keep the RPM from going any higher.  It starts to move the blades to make the blade pitch more coarse to add load to the engine, and does so until the RPM stabilizes at the Max RPM governor setting.  As you keep adding throttle, increasing torque, the governor will increase blade angle more, whatever is required to keep the RPM at the governor setting.  Also, as you start to move, the forward speed starts to unload the propeller by reducing angle of attack, and the blades will coarsen further as required.

The governor doesn't know or care what the blade angle is; it's just a flyweight device like on an old steam engine and all it knows is "speed too high, do this, speed too low, do that". All the prop control does is apply a preload to a spring that determines the speed at which the flyweights will do their thing.

So yes the propeller will move toward coarse pitch because it's already fully fine and the governor has to move it more coarse to limit RPM in that situation.

If you shove the throttle in quickly, causing the RPM to rise very quickly, there may be a slight lag in the governor's response and the prop will overspeed momentarily a little bit (enough to create a noticeable EAAAOOOOWWW sound as RPM passes redline a bit and then slows down as it recovers to the governor setting).

The question is poorly worded.  It should be referring to "constant speed" governed propellers, not variable pitch, which is manually operated and quite rare (way too much work).  And the statement "best angle of attack" really means "angle of attack required to load the engine such that RPM is stablized at the Max RPM setting" (normally redline RPM for takeoff).  And this will always be more coarse from full fine pitch.


Would it be possible to use 3D printed node based structures to make cheaper GA planes? A car boasting 700HP and under the U.S LSA weight limit was just announced by Divergent Technologies. I was curious on peoples thoughts on using this technique in planes. Obviously there are some issues with the surface of the structure bearing load, but I imagine these could be overcome.

3D printing is unlikely to make anything cheaper in the near future. With current printing technologies it's an order or magnitude or two more expensive per unit than volume manufacturing techniques such as extrusion or injection moulding.

It's notable that the company you link to chose to make a supercar rather than a low-cost small car. There's little price competition in that market, as brand loyalty dominates. Most supercars are bought as status symbols or for fun rather than for their actual road performance. Most of the incumbents manufacture very small runs with a lot of hand assembly: exactly the kind of manufacturing that 3D printing is competitive for. On top of that, because of the status symbol marketing, there's huge room for new players to differentiate based on a green image. Tesla has done this in the last few years, which is why some of DMF's marketing material focuses on dissing electric cars.

Runs are small in GA too, so there's potentially a wider niche for these techniques to fit into. The market that would most closely fit IMO is kit aircraft. A kit that's primarily 3D printed parts joined by standard spars, with a flexible outer shell, could have shorter lead times and less tooling cost.

After discussing this with some mechanical engineer colleagues today, they pointed out how 3D printing of metals is now being used as a complement to CNC machining in the rocket industry. For a part that has to be machined from a single piece of metal, they 3D print a shell that's slightly larger than the required shape, and then machine it to the correct shape. It allows you to achieve the tolerances you get from machining (which 3D printing can't yet deliver), but without the waste you get from cutting down a solid block.

It's an aside to the main question, but it's a way that 3D printing could be used to reduce the cost of some components and allow designs that would have been economically infeasible.


Can passengers use headphones during takeoff and landing? On a recent flight from KBP to KIV operated by Ukraine International Airlines (aircraft B737-800) I was asked by the flight attendant to remove my headphones both during takeoff and landing.

Is this common practice because I never saw it happen on other flights?  Are there any EASA regulations regarding this?

Jan Hudec was right.

Passengers are not to wear headphones during critical phases of the flight (understand : takeoff, landing, taxi, emergencies), because this could prevent them to hear announcements or directions made by the crew in case of emergency, and because headset cables could create an obstruction in case of an evacuation.

Also, this would prevent them from listening to the safety briefing.

This safety rule is enforced, as far as I know, by several European airlines.


What is ATR Automatic Thrust Restoration in MD-83? What is ATR Automatic Thrust Restoration  in MD-83 ?

The MD-80 series has two systems that can increase thrust in case an engine fails during takeoff:

Automatic Reserve Thrust (ART)

This system is independent of the throttle position and can increase the thrust of the remaining engine to the maximum rated thrust in case of an engine failure. It can be turned off with a switch on the glareshield, because it must not be used when using a FLEX takeoff thrust.
Automatic Thrust Restoration (ATR)

This system will use the autothrottle servos to increase thrust up to the go-around thrust setting after an engine failure.

  Thrust Recoveries for Engine Failure During Takeoff

  In takeoff mode, two separate systems attempt to provide maximum available
  thrust when the performance of one engine significantly differs from the
  other. These systems are automatic reserve thrust (ART) and automatic
  thrust restoration (ATR).

  Automatic Reserve Thrust (ART) System

  The ART system combines features of the digital flight guidance computer
  (DFGC) and the JT8D-200 fuel control to provide maximum rated thrust in
  the event of an engine failure during a normal thrust takeoff. Upon actuation
  of the ART system, thrust is increased without throttle movement by the
  opening of a solenoid-operated fuel valve in the engine fuel controls of both
  engines.

  The ART system is READY when the airplane is on the ground, the ART
  switch is in AUTO, either slat is extended, both engines are operating at or
  near idle, and the ART system self-test is complete. The ART system is
  subsequently armed when the N1 on both engines reaches 64% RPM.

  The ART system is actuated when the DFGC detects any one of the
  following: 30.2% differential in N1 RPM, invalid N1, DFGC failure,
  electrical power loss, or manual DFGC switching. Upon actuation, the ART
  system increases the EPR of the operating engine(s) from normal takeoff
  EPR to maximum takeoff EPR (an increase of approximately .05 EPR) by
  opening the solenoid-operated fuel valve in the engine fuel control. Once
  ART is actuated, the maximum takeoff EPR limit is displayed on the thrust
  rating indicator, and the EPR gauge. Once actuated, the ART system is
  latched (ART fuel valve remains open) until the ART switch is moved to OFF.

  The ART has an automatic self-test feature. If the ART system fails the selftest, the ART INOP annunciation illuminates. Dispatch is allowed with a failed
  self-test; however, the ART switch must be moved to OFF to disable the ART
  system.

  The ART switch, with AUTO and OFF positions, is on the upper instrument
  panel. Two annunciator lights are on the center instrument panel. The
  READY light indicates ART has successfully passed the self-test. The ART light
  indicates the system has successfully activated.

  Automatic Thrust Restoration (ATR) System

  The Digital Flight Guidance Computer (DFGC) automatic thrust restoration
  (ATR) is a feature, separate from the ART system, that increases thrust under
  certain conditions in the event of an engine failure during takeoff. Once
  activated, the ATR will unclamp the throttles (if the autothrottle system is
  engaged) and move both of them equally until one of the engines reaches the
  Go-Around EPR Limit.

  The ATR is armed if:

  The flight director pitch axis is in takeoff mode,
  The airplane is above 350 feet radio altitude, and
  Both engine EPRs are below the Go-Around EPR limit.

  After arming, the system will activate if the differences between the engines
  are greater than or equal to 0.25 EPR and 7% N1 (in the same direction), or
  (for DFGC models -930) the airplane’s vertical speed decreases to less than
  zero for 5 seconds. In these cases, the throttles will unclamp (if the
  autothrottle system is engaged) and move to the Go-Around EPR limit.

  If ART is armed and the ATR is activated, the EPR limit will be the
  maximum inflight takeoff rating reduced by the same amount that the ART is
  designed to provide. This correction prevents overboosting the engine if the
  ART system subsequently actuates.

(MD-80 FCOM Sec. 18 - Power Plant)


Why aren't aircraft cabins pressurized to sea level pressure? From an article on WHO's website:

  Although aircraft cabins are pressurized, cabin air pressure at cruising altitude is lower than air pressure at sea level. At typical cruising altitudes in the range 11 000–12 200 m (36 000–40 000 feet), air pressure in the cabin is equivalent to the outside air pressure at 1800–2400 m (6000–8000 feet) above sea level.

Why aren't cabins completely pressurized, but instead to 6000-8000', seeing that many passengers wouldn't have to endure sometimes painful popping in the ears?

Two reasons: Longevity and weight. Which really come down to just weight.

Airframes have a limited fatigue life, measured in flight cycles.
The main driving factor for airliner airframe wear is pressurizing and depressurizing them. Each millibar of difference between cabin pressure and outside pressure effectively consumes some percentage of the airframe's fatigue life.

Reducing the cabin altitude means increasing this pressure difference, and thus consuming more of the airframe's life. This could be compensated for with sturdier construction, which adds weight. It would also consume a little more bleed air, requiring slightly heavier packs, which, as well as weight, means a loss of efficiency.

Luxury business jets often maintain a lower cabin altitude, such as 4,000 ft. This eats into their flight cycles, so they can still be switched to the usual 8,000 ft for flights without the owner/VIP inside.
Carbon fiber has a much longer fatigue life, so CFRP fuselages can afford to lower the cabin altitude to 6,000 ft. This pressure altitude can also be maintained in other airliners at flight levels well below their ceiling.

The optimum compromise point is subject to a lot of debate. The highest cabin altitude that could be permitted is 15,000 ft, above which hypoxia-induced loss of consciousness can occur. The regulatory bodies have settled at 8,000 ft, so that's what the manufacturers targeted with most of their aluminum airliners, and that's where airlines prefer to run them even if they have a choice, to get more life out of their planes.


What are the FAA's requirements for an experimental type certificate? What is required by the FAA to obtain an experimental type certificate for a manned prototype aircraft?

Found it. It's easy to get lost in the FAR's, but in case you're curious I managed to find the requirements I was looking for under 14 CFR 21.193:

  An applicant for an experimental certificate must submit the following
  information:

  (a) A statement, in a form and manner prescribed by the FAA setting
  forth the purpose for which the aircraft is to be used.

  (b) Enough data (such as photographs) to identify the aircraft.

  (c) Upon inspection of the aircraft, any pertinent information found
  necessary by the FAA to safeguard the general public.

  (d) In the case of an aircraft to be used for experimental purposes—

  (1) The purpose of the experiment;

  (2) The estimated time or number of flights required for the
  experiment;

  (3) The areas over which the experiment will be conducted; and

  (4) Except for aircraft converted from a previously certificated type
  without appreciable change in the external configuration, three-view
  drawings or three-view dimensioned photographs of the aircraft.

  (e) In the case of a light-sport aircraft assembled from a kit to be
  certificated in accordance with §21.191(i)(2), an applicant must
  provide the following:

  (1) Evidence that an aircraft of the same make and model was
  manufactured and assembled by the aircraft kit manufacturer and issued
  a special airworthiness certificate in the light-sport category.

  (2) The aircraft's operating instructions.

  (3) The aircraft's maintenance and inspection procedures.

  (4) The manufacturer's statement of compliance for the aircraft kit
  used in the aircraft assembly that meets §21.190(c), except that
  instead of meeting §21.190(c)(7), the statement must identify assembly
  instructions for the aircraft that meet an applicable consensus
  standard.

  (5) The aircraft's flight training supplement.

  (6) In addition to paragraphs (e)(1) through (e)(5) of this section,
  for an aircraft kit manufactured outside of the United States,
  evidence that the aircraft kit was manufactured in a country with
  which the United States has a Bilateral Airworthiness Agreement
  concerning airplanes or a Bilateral Aviation Safety Agreement with
  associated Implementation Procedures for Airworthiness concerning
  airplanes, or an equivalent airworthiness agreement.

  [Doc. No. 5085, 29 FR 14569, Oct. 24, 1964, as amended by Amdt. 21-85,
  69 FR 44862, July 27, 2004]


How does the Mil Mi-35M compare to the Boeing AH-64D Apache? (Source left, right)

How does the Mil Mi-35M compare to the Boeing AH-64D Apache?

Both are attack helicopters. I have the following concerns with the Mi-35M:

When compared to the largest U.S. attack helicopters (like the Apache), it looks quite heavy.
It has a cargo compartment that seems to have no use. Looks like the Soviet design was retained to avoid massive redesign.
It doesn't have a reinforced 'cheek' like the Apache does to protect it from bullets of larger caliber.
It doesn't have a mast-mounted radar like the Longbow has. Looks like fire-control is manual.

How do they compare?

TL;DR It's really mission related.

1) not the same role

2) Cargo compartment is important (see below)

3) Soviet doctrine had helicopters fighting with troops so I'm guessing a soldier on the ground is more worried about the dude with the AK-47 and bayonet charging them so they don't have time to take pot shots at choppers

4) Mast mounted radar came later. The original Apache didn't have it and even the new Super Cobra doesn't have it

I'll expand on my comment about the Mi-28 Havoc below but to stab at the Mi-35 you have to look at the Soviet air doctrine when these aircraft were designed.

This student research paper aptly named The Soviet Attack Helicopter describes the role helicopters were seen taking in the Soviet Union

  In April of 1976, Belov reflected an evolutionary change in Soviet attitude toward attack helicopters stating that fire-support helicopters may be regarded as a highly effective weapon for land forces. He felt that these helicopters could be used not only to support subunits on the battlefield but also to destroy various targets independently, to accompany airmobile troops and landing forces both inflight and after landing, to fight tanks and other armored targets and also to destroy enemy aircraft and air-mobile troops both in the air and on the ground.

Contrast this to US forces where there are very defined roles for helicopters. Attack helicopters at the time (Apaches and Cobras) and transport units (Huey and Chinook) had very defined roles. Transport choppers provided some cover fire and limited rocket capability. Attack helicopters provided close air support and sneak attacks on various mechanized and fixed targets.

the soviets though saw helicopters as one in the same. As one author put it in the soviet tactical air doctrine paper from 1976

  The one constant in all Soviet use of tactical air power is that air power is only one component that must be used in concert with other military forces in order to be effective.

So their helicopters were not tools that happen to occasionally transport or support ground troops they saw them as integral components in a land/air strategy.

this brings me to the Mi-28 Havoc. Note that on the wikipedia page it looks similar to an Apache. Swiveling gun turret, guided/unguided rockets, etc... But also note it has a small compartment that can fit 3 people.

Imagine an aircraft goes down: pilot, co-pilot, navigator (or some combo like that). In the US an attack helicopter would provide cover fire if needed. a transport helicopter would come in to retrieve the crewman.

BUT in the Soviet strategy even the smaller Havoc could land quickly and evacuate the wounded! It's a stark contrast in CONOPS.

The Mi-35 is really a big version of this strategy. Bring in lots of troops and stick around with rockets and guns to provide heavy gun fire. Unlike the precise shots that the Apache/Havoc can take; the Mi-35 and even the armed versions of Huey's/Black Hawks provide a 'pray and spray' mentality. A lot of fire on a lot of entrenched troops/light armor in a treeline or foxholes.


What is the device at the tail of the F-16 Block 60? The F-16 Block 60 has a lot of advancements, one of which is the device at the tail. What is it?

For clarification, I believe all these vents (second image) are for said device.

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 IFR flight plan be amended or cancelled whilst in flight? I'm asking, because ForeFlight states in their demo training video that an IFR filed flight plans can only be amended or cancelled up to 47 minutes prior to it being filed (and up to 2 hours after, for VFR flight plans that have been filed. Not sure why that's time restricted at 2 hours?).

website: https://foreflight.com/support/video-library/watch/?v=how-to-filing-icao&list=filing-briefing

But in the movies you see jets owners telling the pilots to alternate their course to an alternative location (even International flights).

Yes, an IFR flightplan can be cancelled at any time. The pilot simply tells ATC "cancelling my IFR flight", then it is cancelled. Depending on airspace classification, ATC may need to issue a clearance to continue as a VFR flight.
However, diverting to another destination than originally planned is not the same as cancelling a flightplan. To do so, the pilot will just inform ATC that they are diverting, and then ATC will provide an appropriate route to fly to get to the new destination. The reporting office at the new destination will, when the flight has landed, send a standard message to the original destination, stating that the flight has landed elsewhere.
Most deviations from your filed flightplan does not actually require an update of the flightplan itself. After all, the flightplan is only the plan you intend to follow at time of departure (or really, at time of filing the plan). Very few flights end up actually following their flightplan to the letter. ATC always keeps a local copy of your flight data, which is updated with any clearances given and other requests that might deviate from your original plan. If the deviation, whatever it may be, affects a downstream ATC sector, it can easily be coordinated verbally. However, if, in some rare case, you need to actually amend your flightplan while in the air, just inform ATC. The controller can either make the required changes (and send related AFTN message) directly, or get in touch with a flight data assistant that can take care of it.


Can you do your PPL solo time in an ultralight? I've been thinking of getting an ultralight as a low cost way to pursue flying.  And I've been wondering, when my instructor finally signs me off for a solo flight, am I allowed to do that in an ultralight?  And, if so, is there equipment I would be required to have that isn't standard on an ultralight?

Nope.

Your solo time must be done in the category and class of aircraft for which you are seeking a pilot certificate (the FAA doesn't come out and say it in those words, but that's what the "aeronautical experience" requirements basically boil down to). You must also pass a pre-solo knowledge exam and receive instruction in the particular make and model of aircraft you will be solo-ing in (the second of which is impossible in an ultralight: You cannot receive dual instruction in that aircraft as by regulation it can only have one seat).

As you don't need a pilot certificate to fly an ultralight you could just get one, get some basic instruction on flying it (from someone who has flown them before), and go fly. Some ultralights are pretty fine basic aircraft thanks to modern materials and construction techniques.

Your private pilot training & solo experience would be helpful in flying certain types of ultralight aircraft, but it's not required as long as you abide by the regulations applicable to ultralights.
Similarly experience in the more "airplane-like" ultralights may help you out in the rest of your private pilot training, but that experience isn't required (and not really "loggable" toward your training, through you can put it in your logbook if you wish -- just log the time as "Ultralight Flying" or something similar.)


How does the FAA determine which format of location identifier to assign to an airport? In the U.S., FAA location identifiers are assigned to registered aerodromes. However, these can have different formats:

3 Letters (e.g. ORD)
1 Number and 2 Letters (e.g. 1AD)
2 Numbers and 1 Letter (e.g. 25M, 8M1, or M72)
2 Letters and 2 Numbers (e.g. TN01, 1CA3, or 50SD)

How does the FAA determine which of these formats should be used when assigning the identifier for an airport?

In short, the scheme is as follows:

Busier airports get 3-letter identifiers.
Less busy public-use airports usually get 2 numbers and a letter, sometimes 1 number and 2 letters.
Less busy private airports (which is almost all private airports) get 2 letters and 2 numbers.

More specifically, the FAA assigns airport identifiers (and location identifiers in general) according to the guidance laid out in section 1-2-7 of JO 7350.9F (PDF).
3 Letter Identifiers
For airports, 3-letter identifiers are assigned to airports that meet the following criteria:

Airports:
(a) with a manned air traffic control facility.
(b) with a navigational aid (NAVAID) within airport boundaries.
(c) that receive scheduled route air carriers.
(d) that receive military airlift services.
(e) designated by the U.S. Customs Service as Airports of Entry.

or

Public use airports commissioning Automated Weather Observations Systems, level III (AWOS-III) or higher that have paved runways 5,000 feet or longer.

1 Number, 2 Letter Identifiers

Most one−number, two−letter identifiers have been assigned to aviation weather reporting and observation stations and special−use locations. Some of these identifiers may be assigned to public−use landing facilities within the United States and its jurisdictions, which do not meet the requirements for identifiers in the three−letter series.

The format of these codes is as follows:

In this identifier series, the number is always in the first position
of the three−character combination.

For example, 1AD would be a valid code.
2 Number, 1 Letter Identifiers

Most one−letter, two−number identifiers are assigned to public−use landing facilities within the United States and its jurisdictions, which do not meet
the requirements for identifiers in the three−letter series.

The format of these codes is as follows:

One−letter, two−number identifiers are keyed by the alphabetical letter. The letter may appear in the first, middle or last position in the combination of
three characters.

For example, 25M, 8M1, or M72 are all valid codes.
2 Number, 2 Letter Identifiers

Two−letter, two−number identifiers are assigned to private−use landing facilities in the United States and its jurisdictions which do not meet the requirements for three−character assignments.

The format of these codes is as follows:

They are keyed by the two−letter Post Office or supplemental abbreviation (listed below) of the state with which they are associated. The two−letter code
appears in the first two, middle, or last two positions of the four−character code.

For example, TN01, 1CA3, or 50SD would be valid codes.
The order continues to list a table of supplemental codes that can be used instead of the state's mail code. This allows for states whose mailing codes wouldn't work well as part of the identifier and also for states which need more than the 300 private airport registration codes possible with a given 2-letter sequence in this format.
Changes to Existing Identifiers
Airport identifiers are preferred to keep the same code once it's assigned, except in exceptional circumstances. According to section 1-2-4 of the same document:

Location identifiers are considered permanent and will not be changed without strong and documented justification, primarily concerning air safety or a significant change of landing facility status.

As a result of this, it's possible for an airport which now meets the qualifications for a 3-letter identifier to still have an identifier containing numbers due to it not having met the requirements for three letters when it was assigned. 8A3, Livingston Municipal Airport is an example of this. It has an AWOS-III and a paved runway longer than 5,000 feet, but still retains the code 8A3, which was assigned before the runway was lengthened.


Would it be possible to use a magnetron beneath glider plane to generate its own thermals? Would it be feasible to install a series of magnetrons or something else on the underside of a gliders fuselage and wings in order to heat the air beneath the glider and ultimately cause the glider to obtain high altitude flight or obtain flight when thermals are not available? If hot air rises would you theoretically be able to artificially heat the air beneath a glider in order to achieve high altitude flight?

I was watching videos about gliders and I noticed that thermal air pockets are often required to achieve altitude gain. I'm a dumb guy so excuse me if this is a ridiculously dumb question.

This would not be feasible.  First of all electromagnetic radiation emitted by magnetrons would heat up the water vapor in the air and not necessarily the air itself.  Molecules must have a dipole for EM heating to work.  Second it is not just the heat, what really creates the lift is the moving air upwards.  If you heat the air underneath the airplane that doesn't mean you will make the air move.  Thermals are typically less effective when close to the ground.  Thirdly, finding thermals on your own is part of the sport.  I think that generating your own thermal would defeat the concept of the sport.

Also gliders don't have to completely rely on thermals to stay up.  Ridge Lift and Wave Lift can be used in mountainous areas where the lift is generated by a moderate wind slamming perpendicular to a mountain ridge forcing the air up.


What mental health standards must a candidate meet in order to qualify for a pilot's medical certificates? What are the mental health standards (if any) that a candidate pilot must meet in order to qualify for a medical certificate?

Answers for Canada, the US, and Europe would be particularly interesting to me.

Canada:

  1.3 The applicant shall have no established medical history or clinical diagnosis which, according to accredited medical conclusion,
  would render the applicant unable to exercise safely the privileges of
  the permit, licence or rating applied for or held, as follows: (a)
  psychosis or established neurosis; (b) alcohol or chemical dependence
  or abuse; (c) a personality or behaviour disorder that has resulted in
  the commission of an overt act; (d) other significant mental
  abnormality

US:

  Unless otherwise directed by the FAA, the Examiner must deny or defer
  if the applicant has a history of: [...] (8) Psychosis; (9) Bipolar
  disorder; (10) Personality disorder that is severe enough to have
  repeatedly manifested itself by overt acts; (11) Substance dependence;
  (12) Substance abuse; [...]

EASA (Europe) (abbreviated):

  AMC1 MED.B.055 Psychiatry   (a) Psychotic disorder   (b) Organic
  mental disorder   (c) Psychotropic substances   (d) Schizophrenia,
  schizotypal or delusional disorder   (e) Mood disorder   (f) Neurotic,
  stress-related or somatoform disorder   (g) Personality or behavioural
  disorder   (h) Disorders due to alcohol or other substance use   (i)
  Deliberate self-harm

  AMC1 MED.B.060 Psychology   (a) Where there is
  suspicion or established evidence that an applicant has a
  psychological disorder, the applicant should be referred for
  psychological opinion and advice.   (b) Established evidence should be
  verifiable information from an identifiable source which evokes doubts
  concerning the mental fitness or personality of a particular
  individual. Sources for this information can be accidents or
  incidents, problems in training or   (c) The psychological evaluation
  may include a collection of biographical data, the administration of
  aptitude as well as personality tests and psychological interview.
  (d) The psychologist should submit a written report to the AME, AeMC
  or licensing authority as appropriate, detailing his/her opinion and
  recommendation.


What data did the earliest HUDs display (for fighter jets)? Ideally I'm looking for a screenshot with a bullet list of data. I started my search at the obvious encyclopedic site and was surprised to learn that the earliest HUDs (on fighter jets) go all the way back to the 40's.

So what data did they display? Presumably it would be a limited set of data compared to today's standards, and I'm very interested in what was considered the most important data for a HUD. Especially, did they have that circular piper showing where your bullets would impact?

Reflector Sight:

The Me 262 Schwalbe, introduced in 1944 as the world's first operational jet fighter aircraft, did not have a full-blown HUD. Instead, like many fighters of WWII, it had a reflector sight which used lenses and reflecting glass to display a reticle. This sort of thing [all of the bright yellow lines you see in the image are fixed together. Although you only really needed a dot and a circle (like the Spitfire), some pilots liked the extra lines to help line up targets that were not dead-ahead. They were favored by pilots over iron-sights because the pilot was not required to position his head in order to see where the guns would fire.

Simple HUD

The MiG-21, introduced in 1959, used a combination of reflector sight and HUD. Though it didn't display the altitude, speed, heading, or attitude in a way that modern fighter pilots may take for granted, it had some ability to track targets with radar and to display predicted target positions for gun or missile use. Here is a guide on how to aim your guns using its sight. Also, explanations of the displays. The following image was posted on a forum thread related to the MiG-23, which came after the MiG-21, but this image looks much like those from the MiG-21 manual. A different image from another author shows you how simple the display could get. Finally, an F-16 in the sights of a MiG-21. You can tell this is a MiG because of the distinctive pitot tube.

Full HUD

The F-14 first flew in 1970. Its HUD was equipped with an artificial horizon, altitude, speed, heading, gun data, missile data, and much more. This is from the F/A-18, which first flew almost a decade later.


Is it possible to play music in the cockpit? I was wondering that if a pilot's flight had been delayed or a pilot had nothing to do, would it be possible for a pilot to play music in the cockpit?

Depending on the equipment in the aircraft, the answer may very well be yes. A lot of modern headsets in civilian aircraft (particularly those with active noise reduction) have bluetooth capability that allows music streaming. Some more modern audio panels even have music inputs now. I even flew in an Archer that had a CD player on the panel and wired into the audio panel.

If you are lucky enough to have an automatic direction finder (ADF) eating up useful load in your aircraft you may be able to tune into AM radio stations. This may have contributed to the crash of Varig Flight 254.

While you are legally allowed to do this (at least in small planes) the sterile cockpit rules that most if not all air carriers have prevent professional pilots from doing so, as @Carlo Felicione points out in the comments


Why nitrogen generation system is only present in centre tank only? I was going through FCOM of A320 and it mentioned that nitrogen generation system is only there for centre tank and not for wing tanks what is the reason for the same?

The inerting system was added to the A320 as a result of a new FAA regulation in 2008:

On 21 July 2008, FAA required
operators and manufacturers
to incorporate a Flammability
Reduction Means (FRM) or Ignition Mitigation Means (IMM)
on fuel tanks having a flammability exposure exceeding certain
thresholds [...]

(Airbus FAST Magazine 44)
Airbus found that only the centre tank was affected by these thresholds required by the FAA:

AIRBUS COMPLIANCE TO THE RULES
Airbus demonstrated that ‘only
the centre tank’ of some of its
existing aircraft has fleet average
flammability exposure exceeding
7% and is affected by the
requirements of the FAR Part 26.
There is no necessity to do any
modification on other tanks.
It concerns the following aircraft:

A320 Family,
A330-200, A340-200,
A340-300, A340-500, A340-600,
A300-600.

(Airbus FAST Magazine 44)
What exactly does fleet average flammability exposure mean? The FAA defines it as follows:

the percentage of the flammability exposure evaluation time
(FEET) each fuel tank ullage is flammable for a fleet of an airplane type operating over
the range of flight lengths in a world-wide range of environmental conditions and fuel
properties as defined in this appendix[, which] means the percent of time each fuel tank ullage is flammable for a
fleet of an airplane type operating over the range of flight lengths.

(FAA Advisory Circular 25.981-2A)
Since the centre tank is usually used first, it will spend more time empty (or almost empty). Fuel vapour is highly combustible (much more than liquid fuel), so the risk is significantly higher for the centre tank.

By the way, the system is not really a nitrogen generation system. It only enriches the nitrogen content of some HEPA filtered bleed air to reduce the oxygen content:

Air Separation Module (ASM) description
It is the core of the Inert Gas Generation
System. The objective is to reduce
the centre wing tank ullage O2
concentration to below 12%
during most conditions. Each ASM
is a semi-permeable hollow fibre
membrane bundle contained in a pressure
containment canister. This canister
is a cylinder with three ports. There is
only one ASM on the A320 Family aircraft,
two on the A330-200 and A340-200/300,
and three on the A340-500/600.

(Airbus FAST Magazine 44)


Is there a special procedure for mid-air refueling in the rain? After reading about mid-air refueling and watching The Perfect Storm, I have a question: is there a special procedure to observe when performing an in-flight refueling in the rain?

Side note: I heard the tanker pilot says something like "we have a wet hose". Is this phrase common?

If you're VMC and simply have rain falling, the procedure doesn't change, and it isn't a big deal (talking fixed wing refueling with a boom here; other communities' procedures/capabilities may be different).  The receiver's windshield will have some amount of rain hitting it, but if it isn't particularly heavy rain then he should still be able to do the AR.

If the visibility is really bad because of the rain, or if you're getting into IMC, then that's the situation you have, irrespective of rain falling or not, and obviously you'd rather have better conditions for doing the refueling.  Going IMC momentarily while you're hooked up may not be a big deal, as you can still see the tanker, but if you lose sight then the first priority is to get positive separation between the two aircraft.


Do planes depreciate like cars? Let's say I was in the market for buying a Cessna. What benefits would buying a new Cessna have over an older one? With cars, the resale value does hit a floor as long as it is safe to drive. Are planes the same? Is the fuel efficiency worth buying a new Cessna or is it more of a status thing?

Do planes depreciate like cars?

Planes do not really depreciate like cars per say but aircraft engines kind of do!

Planes are a bit different than cars due to the certification process being far more verbose. Year to year changes tend to be non-existent or come down to trim/paint options. As such a well maintained old aircraft with a fresh/low time engine may fetch more than a new aircraft with a run out engine.

There are also a lot more factors that go into the value of an aircraft even from airframe to airframe in the same make and model where cars can have some options the avionics combinations for most light aircraft are nearly endless.

  Is the fuel efficiency worth buying a new Cessna or is it more of a status thing?

A brand new Cessna 172 is no more fuel efficient than a 172 from 30 years ago (more or less) because the design largely has not changed. Unlike cars that get small aerodynamic and engine changes often, it's far more complicated to change aircraft designs and deal with the certification so designs remain largely unchanged short of small and limited improvements.

I'm not really sure its a status thing, thats highly opinionated and a bit off topic here.


What is this oddly-shaped plane? I saw this plane yesterday:

What is this plane? And what is the reason for it's odd-looking nose?

It is the Airbus A300-600ST (Super Transporter) Beluga, which is a version of the A300 wide-body airliner modified to carry aircraft parts and oversized cargo.

Source: berlin-aviation-forum.com

The nose is shaped like that as the upper portion is basically a cargo hold and is used to transport oversize cargo, especially aircraft parts.

"F-GSTB - 2 Airbus A.300B4-608ST Beluga Airbus (8634655670)" by aeroprints.com. Licensed under CC BY-SA 3.0 via Commons.

The cockpit was lowered below the cargo deck so that the cargo area could be loaded without having to disconnect any of the vital electric and hydraulic lines running to the rest of the plane. However the A300’s lower fuselage, wings and landing gears were retained.

The following image shows the changes that were made in the nose section from A300 to the Beluga.

Source: allaboutguppys.com


If an approach chart says "GPS required", do I need GNSS capability to fly it? If an aircraft is /Y, /C, or /I (RNAV no GNSS), can they fly an approach chart that says "DME/DME/IRU or GPS required"? GPS in my mind is a GNSS. If you don't have DME/DME/IRU and are RNAV (non-GNSS) capable, can you legally fly the approach?

An example of a chart that has the "DME/DME/IRU or GPS required" notation is here.

If you don't have DME/DME/IRU and are RNAV (non-GNSS) capable, can you legally fly the approach?

The chart the OP refers to is shown below.

As you can see from the STAR (standard terminal arrival), which is not an "approach" you have to have either "GPS" or a "DME/DME/IRU" capable RNAV system. Older RNAV systems that do not have an IRU (inertial reference system) would not qualify for this STAR.


Is it common to change the type of engine during major overhauls? Is it common to change out the type of engine during major overhauls of old aircraft?  For example, replacing a 285 hp engine with a 310 hp.  Would this invalidate the performance specifications found in the aircraft's pilots operating manual?

Not common but not unheard of. Overhauls are the major avenue by which older aircraft variants receive upgrades, effectively becoming newer variants (or functionally equivalent to them). Engine upgrades can be one of the easier changes to make, assuming the new engine was designed to be a "drop-in replacement" (mounts and fuel/electrical connections identical, so you just bolt it on possibly with a token change to the housing). Other changes between variants can be much more in-depth, like stretching the fuselage or altering wing length and profile, which are not typically done to aircraft that have already entered service.

In GA, this tends to be more common, as many of the airframes in the GA fleet are decades old (thanks to strict maintenance requirements keeping them serviceable much longer than the expected useful life of a car), and so the benefit of more modern technology of all kinds, including in the engines, tends to justify the costs. Major airlines very rarely do this kind of thing, especially with engines, as jet engines are ridiculously expensive, and when the engine's reached the end of its useful service life, the airframe usually isn't far behind. It's sometimes done to really big, really expensive aircraft like 747s, and the military has done a few "service life extension programs" that involve replacing engines on venerable airframes like B-52s and C-130s.

As far as invalidating ratings, well yes, the original aircraft specs in the POM would no longer apply after an up-engine. The aircraft, as a unit, must be re-rated both theoretically and empirically by an FAA inspector to determine its new specs, and whether all the components of the aircraft can handle them safely (a more powerful engine does not necessarily mean the aircraft can be rated for a higher "do not exceed" speed, if the limiting factor wasn't the engine but the airframe's ability to take the stress). The easiest types of upgrades to get approved are ones that turn the aircraft into a more powerful factory variant of the airframe; for instance, dropping a 235 engine into what used to be a Cherokee 180. With a few other tweaks to bring the entire aircraft up to the specs of a 235, it can be evaluated as if it were one.


What is the VAC indication? I pilot the plane cessna in the simulator for a long time, and I always saw this VAC indication next to the Ammeter. What is VAC for and how to read it?

In short, it is the vacuum gauge. It measures the vacuum pressure in Inches of Mercury. It runs/powers your non-electrical gyroscopic instruments. Those are your Attitude Indicator, your Directional Gyroscope, and sometimes your Turn Coordinator. These are all necessary to fly by Instrument Flight Rules.

Read these:

PHAK

Airplane Flying Handbook


Trying to identify an aircraft from a photo I'd like to know if anyone can identify an aircraft from this photo. The man in the photo is my grandfather Joseph White. He didn't talk about what he did in the war and we have been trying to put the pieces together for years. Any assistance would be appreciated. This plane might have been captured so it's a larger pool of aircraft than I would be aware of.

Based on the wing/canopy position and yoke rather than joystick, I think this is some version of the Lockheed P-38 Lightning.  Everything I can see in the photo agrees with what I can find online in terms of canopy style, relative position of the wing leading edge, and the relatively unusual (for WWII era) yoke primary control.
http://warbirdsnews.com/warbirds-news/found-lost-squadron-p-38-piloted-by-lt-col-robert-wilson.html
And what might be another photo of the same pilot, credited as the 475th Fighter Group, actually dressed for work:

P-38s of various generations were flown in both Europe and the Pacific -- including the Aleutians, where the heavy jacket would be more appropriate than the Philippines or Coral Sea.  They were, as far as I recall, not flown from carriers, however, so it would be an Army (before the Air Force split) or possibly British livery aircraft; that's not discernible in this tight crop.


Where do extra planes come from? Last night, I had to change planes at LAX because the United Airlines B737 that I was flying on had radio problems and thus could not fly over the ocean. One of the hi-frequency radios had problems, and the pilot said that both radios must function in order for the plane to fly over the ocean. So I flew on another B737 and arrived at Honolulu almost two hours late.

Do airlines keep "spare" planes at major airports in case problems with planes that are scheduled to fly happen? What is the procedure for getting a replacement plane? A plane could not be flown in at a moment's notice, obviously, because it could take hours for it to arrive.

In my experience, having permanent airplanes standing by as spares does not really happen. Based on historical data potential realtime spares, airplanes with potential availability on any given day, can be pinpointed for reschedule or delayed maintenance, should the need arise.

In reality, often the "spare" as you called it, is an airplane that can be pulled from another trip with a subsequent replacement available causing less delay than the flight generating the need for the spare in the first place.

At some airline "hub" locations, maintenance is being performed on aircraft and those aircraft can be used as spares, assuming the checks or maintenance is complete or can be delayed.

Two important points though:

It is extremely costly to have "extra" airplanes standing by to replace an aircraft that may go out of service.  Swapping aircraft is sometimes quite difficult because the type aircraft scheduled may not be available.  An alternate aircraft (different type) poses difficulty because the crew that was going to fly the B737 you were scheduled on, could not fly a substitute Airbus, for example (they either would not be qualified or not current/legal to fly the different type at a moments notice).
The airline's SOC (Systems Operations Control) or similar has a difficult challenge on most occasions dealing with maintenance delays or cancellations. It is not uncommon for the flight to just be cancelled and have the passengers put on later flights.  However, the airline's Operational management people are experienced at minimizing actual delays and maximizing aircraft utilization.


Is it better to increase speed in a climb? In straight and level flight, lift is determined by speed and angle of attack.  If we are heavier, we must go faster to generate more lift, at the same angle of attack.  At the same speed, angle of attack must be increased for more lift, hence the saying "stall speed increases with weight".

We know lift is less than weight in a descent, because the drag vector has a vertical component opposite weight.

We know lift = weight in level flight.

We know the wing is much more efficient than the prop at producing lift.  By simply raising the nose in a condition of 2400 lbs weight and 600 lbs thrust, sin angle × 600 obviously does not equal 2400 - cos angle × 2400.

We know in a climb there is a vertical component opposite lift.

Does this not in effect make the plane "heavier"?

Does this not allow us to keep optimal AOA, and steady state (not curving up or down) flight, at a slightly higher airspeed when climbing?

Should we not pitch to a slightly higher airspeed in a climb for maximum aerodynamic efficiency?

We know in a climb there is a vertical component opposite lift.

  Does this not in effect make the plane "heavier"?

  Does this not allow us to keep optimal AOA, and steady state (not
  curving up or down) flight, at a slightly higher airspeed when
  climbing?

No, a plane is in effect "lighter" in a climb than in level flight.

Climbing "unloads" the wing-- the lift vector is smaller in a steady climb than in level flight

For any given angle-of-attack, the airspeed must be lower in a steady climb than in level flight.

And for any given airspeed, the angle-of-attack must be lower in a steady climb than in level flight.

In a sustained vertical climb, lift must be zero, with thrust supporting the entire aircraft weight (and also overcoming drag).

Covered in detail (including vector diagrams) here-- Does lift equal weight in a climb?

Note: the question stated that the goal was to maximize "aerodynamic efficiency".  This would seem to imply that the goal is minimize fuel burn per altitude gain, or something similar.  Assuming that the engine is equally efficient at all airspeeds, it would seem that this would be achieved by maximizing the L/D ratio, in which case the concepts stated above are relevant.  Since angle-of-attack is tied to L/D ratio, any shift in the correlation between airspeed and angle-of-attack will change the airspeed that we should fly at, although the shift may be too small to notice in actual practice.  For shallow climb angles the Lift vector is really only reduced by a very small amount, and since Lift for a given angle-of-attack varies according to airspeed squared, the resulting shift in the airspeed associated with a given angle-of-attack will be quite small.

While it's good to understand the basic physics at play, we should be clear that in actual practice, it is by no means always optimum to climb at an airspeed that is lower than the airspeed corresponding to the attack that yields the maximum L/D ratio in level flight.  It depends on what parameter we are trying to optimize and on what other variables are at play.  In most aircraft, these other variables will produce changes in the optimum airspeed for climbing that completely dwarf the slight shift in the relationship between angle-of-attack and airspeed that is caused by the "unloading" of the wing during the climb.

We are more often interested in climbing at the maximum possible rate, or the maximum possible angle, than we are in climbing in the most aerodynamically efficient manner.  Particularly in aircraft with piston engines, the difference can be enormous.

In theory, for a fixed amount of Thrust, the steepest climb will be obtained at the angle-of-attack that gives the highest possible L/D ratio, but this will not be the fastest climb.  Climb rate depends on the difference between power-available and power-required.  Even though the speed where minimum power is required is actually slightly below the best L/D speed, in an aircraft with a fixed-pitch prop the speed for best climb rate is usually above the best L/D speed, because of the greater power available when the engine can turn at a higher RPM.  On the other hand, since Thrust equals power divided by speed, in a piston-engine aircraft more Thrust will typically be available at low airspeeds than at high airspeeds, despite the loss of RPM.  Since climb angle depends on the difference between Thrust and Drag, in a piston-engine aircraft the steepest climb angle typically occurs at an airspeed a little below the airspeed that yields the maximum L/D ratio, i.e. at an airspeed a little below the airspeed that yields the minimum amount of Drag.  For general aviation light airplanes with piston engines, these kind of effects related to available Thrust or Power will usually have an effect on the airspeed that yields the maximum climb rate, as well as the airspeed that yields the maximum climb angle, that completely dwarfs the effect due to the slight "unloading" of the wing by the climb angle, and the resulting slight shift in the airspeed that is associated with any given angle-of-attack.

Example-- from this Cessna 152 data sheet--

Best climb angle 55 KIAS

Best glide speed 60 KIAS

Best L/D speed-- not stated

(Theoretical best L/D speed is slightly faster than best glide speed because the drag from the windmilling or stopped propeller biases the best glide speed to be slower than the best L/D speed.)

Best climb rate 67 KIAS

Related ASE questions on the relationship between Vx, V best-glide, and Vy:

How can best glide speed be lower than best rate of climb speed??

Is Vy closer to Vbg with a variable pitch prop


What do the various lights in the overhead aisle light cluster of a Bombardier Q400 NextGen represent? I took this picture of an overhead aisle light cluster in a Bombardier Q400 NextGen.

Copyright: self

I am inquiring about the role of the bottom row of six rectangular lights. From right to left they are yellow, dark blue, dark red, green, orange, and medium red.

My observation regarding these lights:

The seatbelt light, when lit (and accompanied by a single ping), lights up the green light, for about five seconds.
A double ping, with the second ping at a lower frequency than the first ping, lights up the medium red light, for about five seconds.

I presume that these six lights are intended for communicating with cabin crew. I would like to know the detailed meaning of these lights.

This is the so called "area call panel" and it is indeed used to signal the cabin crew. The colours and their respective meaning is not regulated and depends on the aircraft and aircraft manufacturer.
A selection of colors, manufacturer and type according to airliners:

Boeing / McDonnell Douglas:

Pink - Flight crew to FA call ORFA to FA call
Blue - Call to FA from passenger in seat
Amber - Call to FA from passenger in lavatory
Red (717 only) - Lavatory smoke detector set off
Green (DC-9 only) - Unused, included as a placeholder for an unknown function.

Airbus:

Red - Flight crew to FA call OR (some aircraft only) FA to FA
call
Blue - Call to FA from passenger in seat
Amber - Call to FA from passenger in lavatory
Flashing Amber - Lavatory smoke detector set off
Green (some aircraft only) - FA to FA call

Further down you can read, that Bombardier Dash 8 uses solid green for a regular call and flashing amber for emergency call.
A definitive answer can only be found in the respective aircraft or crew manual.


Why is the altimeter unwinding unevenely during a spin? Spencer Suderman recently did a world record 81-turn inverted flat spin, and dropped over 21 thousand feet while doing so. The entire thing is documented on youtube. The spin starts at 3 minutes into the clip. Looking at the footage, in the beginning of the spin, and also (although to a lesser extent) at the end of the spin, the altimeter is unwinding very unevenly, being almost steady for a second and then quickly unwinding 3-500 feet before steadying (or actually increasing the first couple of turns) for another second. Why is that? It seems unreasonable to me that it would actually be leveling out.

It's worth noting that in the middle of descent, when spin is perfectly flat, it's unwinding evenly.

The altimeter works by measurements of the pressure in undisturbed air, also called static pressure. A static port is placed, usually on the side of the hull, perpendicular to the airflow.

During a spin, the airflow will not flow evenly past the static port, but will occasionally flow directly onto the static port. This will cause a rise in measured pressure, leading the altimeter to believe it is lower than it actually is. This cause fluctuations in the indicated altitude.


Safety regulations for take off spectators around airports? In a Greek island, an A320 blasted a child ten meters away, during take off. It was with his family outside the airport (Greek src).

I wonder what are the regulations, if any, for how much people are allowed to approach the airport (I intended to say runway, but some people might not be able to identify it).

I don't expect from a common person to be aware of the dangers that occur at these situations. The airport should protect them, that's why I ask, if there are any regulations that define the min. allowed distance of people outside the airport?

If yes, it would make sense for the airport to have it's fence at that distant, not any closer.

Most airports are intentionally built away from other areas because of practical problems like noise and potential structures getting in the way. There's also the rather significant requirements to build a runway itself (long, relatively flat and level). But there doesn't seem to be any hard minimum safety distances. It seems to be left up to the airport itself to determine safe distances.

One of the best examples I can think of (with limited clearance around the airport) is Princess Juliana International Airport in St. Maarten. The runway approach passes directly over Maho Beach, a road, and then you have a 7000ft runway (the largest flat spot the island can muster). In the picture below, the fence marks the end of the airport.

It produces some spectacular videos of planes passing less than 100ft over the beach and people watching on the beach are impacted by the blast of jets, who must stop at the end and bring their engines up to speed before starting their roll.

The incident mentioned happened at Skiathos Airport, which is also an island airport with limited land for a runway (shorter than St. Maarten at 5300ft).

So it seems to be that if you have a long, flat, and relatively level spot to build a runway, there's nothing to prevent you from building an airport there.


What Is This in The Top of IL-86VKP? What Is This in The Top of IL-86VKP?

Ilyushin Il-80

Source: Wikipedia

The "canoe" is thought to house "advanced" satellite communications equipment. This is a classified aircraft though, so there isn't a lot of publicly available information on exactly what other equipment might be contained in that hump.


Are weather balloon launches NOTAM'ed? Are weather balloon launches NOTAM'ed?

Related, how frequent (periodically and spatially) are they for gathering data on wind-aloft, etc.?

Yes, they are NOTAM'ed. In the FAA case, the FAA wants to know first when you intend to launch, where from (distance and direction from a town on a map), how high you expect to go and what direction you expect it to travel in. 24 hours before launch, you have to call your local Flight Service Station (FSS) and file a Notice to Airmen (NOTAM) giving the launch site, date and time, expected max altitude, expected rate of climb, expected direction of travel and landing spot. Your local FSS will have an 800 number. These people can also give you the winds aloft if you ask. Most pilots have no use for winds aloft over 30,000 feet, so tell the FSS that you're launching a balloon and ask for wind speed and direction for as high as they have data for. This will typically be about 50-60 thousand feet. Try to get the winds aloft for a reporting station to the west of you because 24 hours later, those winds will have likely moved to your location.

The NOTAM will look something like this:

"High altitude balloon release 5.49 WNW of KAGC, E/SE bound reaching Flight Level 600 (60,000 feet) on June 6.  Launching time between 1200 and 1300Z.  E/SE direction of drift.  Landing time no later than 1700Z"


How high can a ramjet go? Yesterday, there was an off-topic question on Space.SE, asking if a ramjet-missile could place itself in orbit. Impossible for a ramjet, obviously, as it requires a high speed flow of air and is too slow to reach orbital velocity.
However, this got me thinking about a ramjets altitude limitations:
How high could a ramjet-powered aircraft or missile possibly go? And how does the speed the jet is traveling at effect the highest possible altitude?

Here's a quick estimate for this.
The maximum altitude for level flight is when the engine can't produce the thrust required to fly fast enough to generate the lift required to balance the weight.
Ramjets work best at around Mach 3 and can operate up to Mach 6
Lift is proportional to speed squared and air density. So doubling the speed allows the plane to fly in air that is a quarter of the density.
The equations for calculating air density with altitude are moderately complex but there are a couple of tables here that show that the density at 32km is about eight times less than at 20km.
So if the SR-71 flew at Mach 3 and 25km, and if you could make a SR-71 that could fly at Mach 6, it might manage another 5 or 10 km in altitude.
Obviously that's a massive simplification because if switching engine technologies would have improved the SR-71's speed, they would have done it. Also because the SR-71 engines were ramjets when it was flying fast.
A ram jet won't get you into orbit because orbit is not just a matter of flying high enough but of reaching orbital speed - the speed where the curve of your naturally falling trajectory will miss the earth due to the earth's curvature. It's about Mach 25. And (as Ross points out) even if you could reach Mach 25, you can't circularise the orbit with an air breathing engine because that requires thrust at the highest point.


On commercial jets, is asymmetric thrust used as part of normal operations? I know that when manoeuvring on the ground, asymmetric thrust is often used, for example to assist in turns when taxiing.

Are there other circumstances in normal operations which might call for the use of deliberate asymmetric thrust in manoeuvring?

I am specifically not asking about emergency or other abnormal ops, flight testing or auto-throttle operation.  I could rephrase the question as "in day-to-day ops of flying an multi-engine commercial jet, is asymmetric thrust ever used to manoeuvre the aircraft when not on the ground?".

This paper from Boeing sheds a light on the subject:

  [A]n intentional engine throttle up or down could create a desired yawing moment followed by a desired rolling moment. Using asymmetric thrust to control roll is not precise because of the lag time associated with engine spool-up or spool-down and should be avoided unless no other means of roll control are available.

While the paper is admittedly about righting the plane from an in flight upset, and is therefore based on a disaster scenario, the message still applies to everyday flight: asymetrical thrust is not the preferred method of control, as the delay between adjusting the throttle and the actual thrust change makes it less precise for maneuvering than the main control surfaces.


Why doesn't the landing gear get raised on the first flight of a new airplane? This image shows the A350 first takeoff high in the air and the landing gear is still down. Why didn't they retract it?

Test flying is thoroughly planned, and of the many things to test during development, the landing gear is just a minor part. In the first flight the goal is to check out basic functionality and how well the low-speed performance was predicted. The landing gear can wait for one of the later flights. You can see in the photo of the A350 that the slats are extended and the flaps are in take-off position. The pilots are busy testing handling in take-off configuration, and for that the gear must be down. You can be sure that they also tested the landing configuration at altitude before going down to land.

Generally, the tested envelope of the aircraft will be expanded step by step. Since every flight will contain a take-off segment, it is prudent to check out this part of the envelope first. Once the low-speed regime is tested, consecutive flights will take the aircraft to higher speeds, and only then will it be necessary to retract the gear.

Also, the first flight of a newly developed aircraft has become a ceremonial affair. After having spent hundreds of millions of dollars or euro, and with all the media attention, nobody wants to live through the embarrassement of a gear failure on occasion of the first flight.

This was not always the case. The F-100 went supersonic on its second flight; taking this kind of risk would be unimaginable today without the pressure of an arms race.


What material and shape should be used for angle of attack sensors? Does the material and shape of the vane for an angle of attack sensor have to be identical to the material and shape of the wing? What properties should I consider?

A wide variety of materials would suffice as an AOA sensor merely aligns itself with the wind as a weather vane and does not carry load.  Any non-warping reasonably strong material such as aluminum plate can be used in the design.

Since we are only measuring wind direction, look no further than old style delta shaped weather vanes, also found on turbine style wind mills.

Another quick AOA sensor could be a smoke trail, a ribbon, or a string. It just needs to follow the wind stream.

A symmetrical wing shape would work fine, a flat plate is easier to construct and is adequate
to the task.


What is this orange container labeled "Flight kit wheel"? What is this orange container for?
It reads

  Flight kit wheel. Do not remove.

What's a "flight kit wheel"?

Short answer
Corsair is a small airline, with a limited number of aircraft, serving airports in remote islands from Paris. For their economical survival their aircraft must keep a high operational ratio. However:

The airline may not have a maintenance facility at destination, either a owned facility or an agreement for maintenance services from another company locally based.

The facility may not have a satisfactory stock of spare parts for their aircraft or the required tools, and no possibility to obtain them in a very short time, even from their main base.

A common solution is to bring parts aboard, in particular MEL components. It's a balance between the cost to carry the container and the cost of extra wait time (better said by FreeMan in a comment below: The weight penalty is much lower than the wait penalty.)
These containers marked Flight kit, Fly away kit (FAK), Do not unload, Do not offload, etc, contain components or tools intended to remain on board and be used at the next stopover in case of necessity.
It's relatively common to see FAK for spare wheels. One of the reasons is when the crew executes a rejected take-off just prior to V1 speed on a large aircraft, brakes are subject to intense heating propagated to the wheels. Tires inflated with nitrogen at about 1,300 kPa (that's about 13 bars or 200 psi) could blow out beyond a certain temperature, causing damages/injuries. To prevent such explosion, wheels are fitted with fusible plugs melting to allow tires to deflate safely.
After such event, the plugs (and possibly the tire) have to be replaced. A common option is to change the whole wheel and perform inspection and repairs later. The kit contains the necessary tooling and parts for this replacement. This might take 30 minutes or so.
As FreeMan also mentions, sometimes the mechanic who is going to replace the wheel is onboard. That was the case (at the time the photo was shot) for Corsair for certain destinations where there is no permanent maintenance team at the stopover.
Corsair, a small airline serving remote locations
And actually Corsair is a small French airline based at Paris-Orly (LFPO), which has a taste of holidays. Their 5 aircraft take people from Paris to beautiful beaches on islands where airports don't have large maintenance facilities (Fort-de-France, Pointe-à-Pitre, La Réunion, Saint Martin, Palma ...)
For a long time Corsair used Boeing 747 Classic, meaning also less common spare parts.
In such a small airline, when an aircraft is grounded the schedule of the others is indeed disrupted, the shorter, the better.
Flight kit

Loading a flight kit, source Linde

Flight kit, Air France (translates to "Fly away kit, do not unload"). Photo by A380spotter at Flickr

Flight kit wheels in cargo hold (Malawi elections inspection). Source
Secured content
Parts in the container are secured to prevent them from moving.

AKN FSK container for Air France (Source)

(source)
See also: Do any aircraft carry spare parts for making repairs?

Corsair, formerly Corse Air, comes from Corse island (the birth place of Napoleon Bonaparte). Their business has known ups and downs several times, they are now part of Dubreuil Group. Corsair 747 had over time famous tail numbers: F-GSEA, F-GSEX, F-GSUN, F-GSKY, F-HLOV, etc.

F-GSEA landing at Princess Juliana. Source: JetPhotos, photo by Rogier van der Velde


How easy is it to make a connection to the aircraft pitot-static system? I've recently discovered the device named Levil 2 AW which gives complete navigation functionalities, including Air Data computations once it is connected to the pitot-static system.

In this regard, generally speaking, is it really so easy to connect to the aircraft pitot-static system as it appears from both product description and related videos?

It's very easy to connect a component to the pitot and static systems: It's literally just basic plumbing (install a T fitting and connect the lines). For IFR certified aircraft a static system test will also be required (and a pitot pressure leakdown test would be advisable if the pitot system is opened).

The regulatory issues surrounding the installation are more complex regarding what kinds of devices may be installed on a certificated airframe and under what conditions they such devices could be used as a primary or standby reference for flying the aircraft, as Ron alluded to.


What is the range of TCAS? The traffic collision avoidance system has two versions, TCAS I and TCAS II.

I know for sure that TCAS I has a range of 40 nautical miles, but what is the range for TCAS II?

Short answer

If a single range should be stated for ACAS II, it would be the reliable range of 14 NM, even if targets can displayed by current TCAS II up to 30/40 NM.

Reliable means here: a track can be established with a probability of at least 90 per cent for aircraft within the surveillance range. The reliable range of 14 NM is achievable with a ground plane antenna, a power of 250 W and a Mode S sensitivity of –74 dBm.

The mean number of aircraft in a spherical volume is proportional to the cubed radius. Each aircraft tracked by a ACAS system must be interrogated, and its position/altitude data stored. This creates stress both on the ACAS equipment and on the radio spectrum used for ATC (SSR and ADS-B in addition of ACAS). The current balance between stress and benefit is a range of 14NM which can be reduced to 4.5 NM if the number of aircraft or the number of ground interrogators prevent managing the nominal range. The spectrum stress should be relieved with the forthcoming ACAS-X.

In addition, while the nominal monitoring range is 14 NM and the guaranteed range is 4.5 NM, RA/TA are issued based on estimated time before separation failure (more accurately before the closest point of approach):

From Eurocontrol ACAS guide

(In the answer, ACAS is related the principle, TCAS is the technical implementation of the principle.)

Diversity of ranges

There are different range values that can be considered:

Overall pulse detection range is 30 NM.
Reliable surveillance range is 14 NM.
Recommended RA range is 12 NM.
Guaranteed range is 4.5 NM.

The range must be limited because it impacts the number of transponder addresses to be stored for a given transponder density as well as the number of interrogations within a volume, hence radio spectrum use and reliability.

ACAS II recommendations by ICAO

ACAS II ICAO recommendations are found in Doc 9863, Airborne Collision Avoidance System (ACAS) Manual:

Interrogation pulse detection range is 14 NM for Mode A/C and 30 NM for Mode S.
The equipment should have the capacity for surveillance of any mix of Mode A/C or Mode S targets  up  to  at  least  30  aircraft.
Surveillance must be reliable within 14 NM, with an aircraft density of 0.3 aircraft per square NM within 5 NM (and up to 142 aircraft within 30 NM).
The equipment should assess as possible collision threats only those targets within a maximum range of 12 NM. No target outside this range should be eligible to generate an RA.
As density increases, reliability decreases.
If the overall target count ever exceeds the surveillance capacity at any range up to 14 NM, the long-range targets may be dropped.
The system reliability is guaranteed within the minimum range of 4.5 NM. This radius is deemed adequate for providing protection for up to 500 kt encounter.

TCAS version 7.1

TCAS II is the sole implementation of ACAS II which fully comply with ACAS II. The reference (paying) documents are: DO-185B (RTCA) and ED-143 (EUROCAE).

From the EASA document ACAS Guide

  TCAS II can simultaneously track up to 30 aircraft, within a nominal
  range of 14 NM for Mode A/C targets and 30 NM for Mode S targets. In
  implementations that allow for the use of the Mode S extended
  squitter, the normal surveillance range may be increased beyond the
  nominal 14 NM. However, this information is not used for collision
  avoidance purposes.

This is confirmed in FAA document Introduction to TCAS II V7.1

  TCAS has a requirement to provide reliable surveillance out to a range
  of 14 nmi and in traffic densities of up to 0.3 aircraft per square
  nautical mile. [...] TCAS can simultaneously track up to 30
  transponder-equipped aircraft within a nominal range of 30 nmi.


Why can't I ever get my right ear to pop on descent in a plane? Whenever I'm flying, there's a period of descent where my right ear just refuses to pop. This has been bothering me for at least ten years.
There seems to be a long stage of descent where my ear is just in agony. I've tried chewing gum, closing my nose and lightly blowing, opening my mouth, everything. However, when descending into landing (I can see cars at this point) it will start to pop.

Otherwise, it'll pop when I swallow at this stage or even while I'm walking around in the airport. The only thing that makes it pop early and at the same time as my left ear would be when I yawn.

When it does pop, it actually hurts sometimes. It has a very distinct pop, too. Instead of a light pop, it sort of stutters a bit, like it pops twice, and it's much louder.

This phenomenon seems to be very unique to when I'm flying on a commercial airline and descending. It has never happened upon ascension, and from the few times I've driven into mountains it hasn't happened, although that hasn't happened enough to be sure.

What about the descent makes this happen? Is there anything I can do to fix this issue?

The eustachian tube is a vent line that connects your inner ear to the back of your throat. Like the sinuses, higher pressure air flows outbound from the inner ear (when cabin pressure is dropping) with pressure changes easier than inbound (when cabin pressure is rising).

So the air trying to get back in on descent has a harder time than when it was leaking out unnoticeably on the climb, and a pressure differential builds up before it equalizes the pressure - the pop.  Part of the tube is through cartilage and it's helped to open more by mechanically "massaging" it so to speak by moving your jaw.

It sounds like the tube for your right ear, which is partly in cartilage and partly in bone, is misshapen enough that it takes an abnormally high pressure differential to equalize pressure when the pressure change happens quickly like on an airplane.  This is putting a lot of stress on your eardrum (which is what the pain is from).

Decongestants often help but if it is a severe chronic problem, which yours sounds like, as a last resort there is a procedure that is usually done temporarily on babies (where the tube is blocked until they grow more - one of my kids had one put in, which falls out on its own later), called a shunt, where a doctor implants a tube across your ear drum to allow the inner ear to vent that way.

Anyway, you should see a doc about it if it's that bad.


What is the cable connected to a plane for? I've seen that airplanes are connected to some wire like in the picture. What is it's name and what is it for?

This is a ground power unit (GPU) which supplies the aircraft with electricity while the generators or the auxiliary power unit (APU) are not running. This is important especially during boarding, when the cabin lighting needs to remain on for passengers to embark or disembark. The GPU is also used to start the APU, which in turn provides electricity to start the engines and the generators.

  A ground power unit (GPU) is a vehicle capable of supplying power to aircraft parked on the ground. Ground power units may also be built into the jetway, making it even easier to supply electrical power to aircraft. Many aircraft require 28 V of direct current and 115 V 400 Hz of alternating current. The electric energy is carried from a generator to a connection on the aircraft via 3 phase 4-wire insulated cable capable of handling 261 amps (90 kVA). These connectors are standard for all aircraft, as defined in ISO 6858.
  Source: Wikipedia

Related Questions:

Can large airliners be operated without ground support?

How are turbine engines started?


How does a vertically higher center of gravity affect handling? Much of the discussion of the center of gravity of the aircraft is focused on the longitudinal axis, i.e. front and back. How does the vertical position of the CG affects the handling characteristics?

For example, the Boeing Dreamlifter and the Airbus A300-600ST both have their cargo stored in the upper portion of the airframe. Are these aircraft easier to "flip over"?

As long as flight is coordinated, the vertical position of the center of gravity (cg) is of minor importance. It will show in issues like thrust changes, when acceleration will cause higher trim changes because of the increased lever arm between the inertial forces and the thrust forces.

This will only change when flight is no longer coordinated and the aircraft sideslips. Now the big cargo volume is more important than the cg location because it will contribute a considerable side force. Also, it will need additional means of lateral stabilisation because the big fairing will destabilise the aircraft in yaw. Still, the lever arm between the cg and the lift force vector will be much, much smaller than the lever arm of the ailerons, and a little aileron deflection will be enough to stabilise the aircraft.

Maneuvering will look funny to crews used to fly the unmodified version of the same airplane, because now a roll manoeuver will induce a lateral motion at the location of the cockpit which was not there before. Same goes for eigenmodes like the Dutch roll which will be more noticeable for the crew because their cockpit sways laterally.

"Flipping over" needs deliberate commands from the pilot; this is no different in aircraft with unusual vertical cg positions. The most extreme is probably the VM-T "Atlant" version of the Russian M-4 Molot bomber.

M-4 Molot version VM-T Atlant with Buran booster tank (picture source)


What is this fighter jet at Weymouth NAS? The picture was taken at Weymouth NAS in about 1988

It's a Panavia Tornado.

Found a site with that picture and others from the same air show. Here is a better picture of one in the same markings. It is part of the RAF No. 5 Squadron, which switched from the English Electric Lightning to the Tornado in 1988. The squadron uses a maple leaf to commemorate their link to the Canadian Corps in World War 1.

Source


How can the cruise speed be larger than Vne? I recently read the POH for a M20V, the advertising for this aircraft states that the top speed is 242 KIAS. The POH gives the Vne at 196/195 KCAL/KIAS.
I have found a similar discrepancy, the Vl3 (light sport aircraft) mentions the aircraft has a Vne of 165 KIAS, yet one of the engine choices gives the plane a max cruise speed of 195. I find these numbers confusing can anyone shed a light on this?

The reason is that cruise speeds are usually given in TAS (True AirSpeed) rather than IAS (Indicated AirSpeed) or CAS (Calibrated AirSpeed). See e.g. this answer for details on what these speeds are.
Have a look at the following plot showing TAS as a function of altitude for the two Vne speeds you gave (assuming ISA conditions):

You can see that the claimed cruise speeds are achievable above 14,000 ft for the M20 and above 11,000 ft for the VL3 without exceeding Vne.
You said that advertisement for the M20V claimed a top speed of 242 KIAS, but I think that is a mistake. It should be KTAS, not KIAS. Wikipedia also claims:

Cruise speed: 242 kn (278 mph, 448 km/h) (TAS)

(Wikipedia - Mooney M20)


Is there a public NOTAM archive that's searchable by airport? Pilotweb lists NOTAMs currently in effect. Is it possible to view or sort the history for a particular airport?

On Pilotweb, there's a "Federal NOTAM System (FNS)" section on the right side of the screen. If you select "NOTAM Search" it takes you to another NOTAM search tool. If you then select "Archive" from the drop-down list, you can search by date and location.


Is the phraseology in the early portion of the movie The Net realistic? Bear with me for a moment; I know that this is based on a movie scene, but there's a real question at the end.

Early in the 1995 movie The Net, there's a scene where a programmer is flying their Cessna at or near dawn, approaching the destination airport. This is a night flight, so it would presumably be an IFR flight with all of what that means, or rather meant in the mid-90s. We get to hear some communication between the pilot and ATC:

  (pilot) Burbank tower, Cessna seven-three-nine-Mike-Bravo, intercepting approach course, ILS runway eight.

  (ATC) 39 Mike Bravo, we've lost radar contact. Say your position and altitude.

  (pilot) Just passing the middle marker at 1300 feet.

  (ATC) 39 Mike Bravo, that's a negative. Verify your position and check your instruments.

  (pilot) All normal, for crying out loud, you must be able to see my lights.

  (ATC) That's a negative. Execute a missed approach immediately. Contact approach control on one-two-four point five.

A moment later,

   the airplane crashes into what appears like it could be power station chimneys, and turns into a fireball, killing the pilot.

That ATC exchange has always bothered me. I can see a few things that feel obviously wrong:

It seems awfully late, especially in IFR towards a big airport (assuming that's Hollywood-Burbank, which goes nicely with a later in-movie statement that this happened "outside L.A."), to contact ATC only by the time you are well into the final approach.
If this is an IFR flight, shouldn't the pilot be following a filed flightplan, and wouldn't someone notice if the aircraft strays too far from its intended course and at least ask the pilot what's going on then rather than wait until it is well into populated or industrial areas? (Note: I can't tell from the movie if the plane supposedly has a transponder or not.)
By the time of passing the middle marker, shouldn't the pilot have the runway clearly in sight and at the very least be lining up with it, if not already be fully lined up with it? This is in moderate darkness, but it doesn't appear to be in otherwise difficult conditions; no visible fog, for instance, even in aircraft-exterior shots.

If someone wants to comment on the above as well, feel free to. However, my main question is this: if this situation were to somehow develop in real life, then is the phraseology realistic? Would ATC say that they have "lost" radar contact? Since the aircraft is obviously in the wrong place by that time, it would seem like they should never have had radar contact in the first place. In such a situation, I (as a non-pilot) would expect ATC to request an ident, possibly verifying the transponder code as well.

"Radar contact lost" is standard phraseology.  Most typically it's used when an aircraft far from the radar antenna is no longer being picked up, and it's just an advisory that "we can talk to you but we can't still see you."  (Remote VHF antennas are cheaper & easier to put up in remote places than radar transmitters.)

As for the scenario itself, initial contact with the tower is hardly the point where ATC would first notice that the aircraft wasn't going where it should be.  To get TO the ILS course, you'd typically have Approach Control issuing radar vectors to the aircraft, ending up with "N1234X, 3 miles from Van Nuys, fly heading 100 until established, cleared ILS runway 8 at Burbank."  If the aircraft flies through the course (for whatever reason; it sounds like in the movie the implication is that his navigation equipment has been hacked), they'd issue another vector, cancel his approach clearance & tell him to climb, or whatever.

Also, ATC (i.e. Approach Control, even more so than Tower) will get automated low altitude alerts when an aircraft is below set altitudes.  If an aircraft in radar contact was descending into terrain (and not on final to a runway), well before the radar loses line-of-sight with the aircraft, the controller would issue something along the lines of "N1234X, low altitude alert, check altimeter 30.05, climb and maintain 2000'."

There are non-radar environments where pilot mistakes have put perfectly flyable aircraft into the terrain without any opportunity for ATC intervention.  There have been cases within radar coverage where misread instruments, usually only when combined with an additional pilot error, have put aircraft into terrain or obstacles short of the landing runway.  The smokestacks referenced sounds like a prominent feature well north of Burbank, so at a minimum there's some "artistic license" involved in claiming that a hacked ILS could put the aircraft that far off course in that direction without ATC catching it well in advance of things getting to the point of a crash.

Also, an ILS receiver would be awfully hard to hack, no matter what sort of evil programming genius you are.  You could disable it in several different ways (pair of wire cutters would do that), but the malfunction would be obvious to the pilot early on.  To have the receiver seem perfectly normal but in fact guiding the pilot down too soon would really require broadcasting false signals to the aircraft in real time in a way that an ILS ground station probably can't do -- at least not without triggering a warning in the monitoring equipment that ends up shutting it down.  And even then, when the pilot gets to 200' above the runway elevation, if HE doesn't see the runway lights, he should be going around.

All in all, this scenario has its weaknesses.  The idea that a hacker could create enough problems to bring down a plane is actually more credible now than in 1995, but even so, the most likely problems are a lot less dramatic than what's described -- "hey, where'd all my electronic charts go?"  Aviation has a LOT of safeguards to prevent exactly this sort of scenario from playing out, even with state-sponsored bad guys as the potential threat.

But, it made for a fun movie, so suspension of disbelief and all, right?


Why isn't the arresting hook always used on land? Watching Jet Stream, about training to fly the CF-18 Hornet, they comment that the jet was originally certified as a Navy plane, landing on aircraft carriers with an arresting cable.

Usually, when landing on land, they land hard and fast and take a mile of runway to come to a stop; but during an emergency, they use the tailhook which brings the jet to a stop after only 1,000ft.

My question is: why don't they always use this to land?

Here's a short clip I've taken from the show:

There is a lot of stress placed on the airframe when you use the tailhoook. You can see the skin buckling in the picture below behind the landing gear. I'll admit, you probably wouldn't land intentionally with this sort of technique on land but if you catch the wire during the flare it could probably pull you down pretty hard. For these types of landing and it would be difficult to get it right every time.
(Like  I wrote in the comments, I do realize that the aircraft below has not yet caught the cable. When you flare, and you might catch the cable mid-air if you have a nose-high attitude, and slam down hard as it pulls you backwards and you loose lift, or you do a non-flare like carrier pilots, also very hard. IMO I think either would end up like the landing below.)

You have no ability to control the aircraft and you end up stopping and rolling backwards on the runway. You can only be one aircraft at a time and you cannot roll off straight away, wasting time.

You'd have to have an arresting gear system and along with that more staff and maintenance.

At least on aircraft carriers, I believe the arresting cable has a limit of only 250 catches for safety reasons. Even if it the limit was greater on land, you'd have to have people changing the cables on a regular basis.

You'd still have to have conventional brakes which you could just as well use.