106 votes
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Why is Python used on aircraft although it may not be certifiable?

Just because aviation developers use Python, does not mean that Python actually goes flying. Lots of aviation development is about testing, stressing, validating, analyzing, and documenting the code ...
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69 votes
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How dissimilar are redundant flight control computers?

As far as Airbus is concerned: Each unit is composed of two dissimilar boards, one driving the output and the other checking it. Dissimilar means both different CPUs and chipsets (A320 uses i386 (...
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66 votes

Why don't all commercial aircraft transmit GPS data in real time?

Most commercial aircraft transmit their GPS-based position twice per second. This is part of their Automatic Dependent Surveillance – Broadcast (ADS–B) broadcasts. The problem with providing world-...
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52 votes
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Are fighter jets designed to be so inherently unstable that a human can't fly one unassisted?

My short answer: Stability is reduced by shifting the center of gravity aft. Shifting it past the neutral point makes the airplane unstable, so movements away from the trimmed state are accelerated. ...
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52 votes
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Why are on-board computers allowed to change controls without notifying the pilots?

There is a general design principle, that some, but not all, of the behavior of the flight guidance system or autopilot should be visible to the pilot. Usually automatic engagement or disengagement ...
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45 votes
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What programming languages are used for equipment onboard aircraft?

There are no language recommendations or requirements, other than what is sensible given the verification requirements in the various standards (e.g., DO-178B/C). For the highest design assurance ...
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  • 566
43 votes
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Do safety-critical avionics systems run Linux?

None of the avionics systems I've worked on have used Linux or any consumer-type operating system. There are a few main issues. First is the practical. Most safety-critical avionics involve a ...
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40 votes
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How does TACAN work?

How is TACAN different from the VHF Omnidirectional Range (VOR) system? A very short question, but the answer calls for describing several techniques which are by themselves difficult to summarize ...
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39 votes
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How does WiFi work on an aircraft?

The small bulb houses the antenna that provides the satellite communications for the internet link. Inside the aircraft several wireless access points provide a WIFI signal to the passenger's ...
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39 votes

How dissimilar are redundant flight control computers?

Redundancy is not only achieved by multiplying the computers, but also by diversifying them. On Airbus airliners, two different computers are used (one with Intel chips, the other with Motorola chips ...
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38 votes
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What exactly did this mechanic sabotage on the American Airlines 737, and how dangerous was it?

It's a serious crime, but what that guy did, only affecting one system out of three, would be unlikely to cause a crash if the pilots were half way reasonably competent. The take-off would be ...
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  • 103k
35 votes

Why is Python used on aircraft although it may not be certifiable?

As a software engineer who works at a defence company that develops and sells mission critical (but not safety critical) systems, I can confirm that there's a pretty even split between development in ...
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  • 451
34 votes
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How is varying modulation depth achieved by localizer ground transmitters?

The beam strength decreases as you move away from it's own centreline, so is it actually that the entire modulated signal strength decreases which when de-modulated is effectively a difference in ...
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  • 67.6k
33 votes

Do safety-critical avionics systems run Linux?

The short answer is that no safety-critical avionics systems that I'm aware of use Linux, and the highest criticality systems often don't use a commercial operating system at all. However, Linux is ...
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  • 6,325
33 votes

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

According to BBC's description, he blocked one of the pitot tubes. (...) a piece of foam was found glued inside a navigation system part which stopped it from functioning. It was reportedly inside ...
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32 votes

Why is the 5G rollout a problem in the USA but apparently nowhere else?

If you read the FAA’s statements (not media reports) closely, you will find their complaint is merely that it hasn’t been proven not to be a problem, not that they actually expect a problem or have ...
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30 votes
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Why are critical flight computers redundant?

Failure modes to consider: Overheating. This changes the chip's timing properties and eventually results in error. This can manifest as single-bit errors in the middle of seemingly normal operation; ...
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30 votes
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What are these boxes built into the tails of some fighters?

You're right. It's the ECM/EW antenna/equipment (fairing) in all the aircrafts except Typhoon. This photo shows the details of EW/ECM suite in Gripen. Source: www.w54.biz In Typhoon, it is the ...
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30 votes

Why is the input power of an ADS-B Transponder much lower than its rated transmission output power?

The rated TX power is the maximum power emitted while transmitting. The electrical input power is much lower, because the design of the transponder is such that it accumulates energy from the input at ...
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  • 74.2k
28 votes

Why are critical flight computers redundant?

As other answer pointed out: A CPU can fail. Either partially (giving erroneous answers), or totally. Moreover all computer are subject to cosmic radiations that can once in a while flip a bit in ...
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27 votes
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Do planes have odometers?

A Hobbs meter measures the time spent in a general aviation aircraft with the power on. Planes differ in that time is easier to record than distance. For a given airspeed, the distance covered by the ...
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  • 120k
26 votes

How does an alpha (AoA) vane work?

From what I have studied at my instrumentation course, it rotates and reads the angle between the current position and the reference position. You then have several (3-4) of them around the fuselage ...
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26 votes
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Like transponders, can flight recorders be turned off?

There is no switch for the FDR, but there is a circuit breaker and by pulling this you are removing aircraft power from the FDR. However, this does not mean you are necessarily turning it off, as ...
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  • 34.8k
26 votes
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Why is it hard to see G1000 with sunglasses?

The screens are LCDs, which have a polarized filter layer over them. That layer is usually placed at a 45° so they are misaligned with your polarized sunglasses which are aligned vertically. You can ...
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25 votes
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How does the ADF null positions find where the NDB is?

Short answer Do you find the null position, then assume it's 90 degrees from the beacon? That's correct. For the antenna pattern shown in the question, the angle between direction of nulls and peaks ...
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25 votes
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What kind of delay does the A320's fly-by-wire system add?

Yes there will be a delay, but the delay caused by the control loop is really tiny. I've seen position control loops run successfully and stable at a couple of hundred Hz for simulator motion systems, ...
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25 votes
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What CPU does the F-16 use?

MIL-STD-1760A is simply the standard that a processor must conform to, and is not an actual model of CPU. There are actually a lot of independent computers in a military aircraft, each with specific ...
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25 votes
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What is the difference between autopilot and fly-by-wire system?

An autopilot can fly the aircraft based on pilot selected modes. The autopilot therefore reduces the pilot's workload by replacing manual inputs via the yoke or sidestick. A fly-by-wire (FBW) system ...
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25 votes
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Why is the 5G rollout a problem in the USA but apparently nowhere else?

Since you are asking specifically about the 3.7–3.98 GHz band, the answer is that most of the world uses the 3.3–3.8 GHz band. The 3.7–3.98 GHz band was seen as much less important until US operators (...
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24 votes
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Why do helicopters and airplanes use different headset plugs?

It's a holdover from the old days when microphone technology wasn't as advanced. The military adopted "dynamic microphones" as the standard, which were less noisy than the alternative "carbon ...
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