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107 votes
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How did the 9/11 hijackers find their way to New York City?

Several of the hijackers, including Mohamed Atta, held at least private pilot certificates and had undergone ATP level jet training in DC9 and 737 full motion simulators in December of 2000. Atta ...
Romeo_4808N's user avatar
81 votes
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Why was Pan Am Flight 103 flying over Lockerbie?

The direct route you show is actually only a straight line on your map projection. The surface of the Earth is curved and the straight line between London Heathrow and New York JFK looks like this (...
Bianfable's user avatar
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80 votes
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Why don’t airplanes use turn signals?

At uncontrolled airports, there is rarely enough traffic for signals to be needed, and pilots should (though are not required to) communicate with each other on CTAF—an option that cars do not have. ...
StephenS's user avatar
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75 votes
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Explaining a "Great Circle Route" to young Civil Air Patrol cadets

I would recommend that you don't introduce the term first and then try to explain it verbally, but demonstrate it in an interactive, hands-on practical way instead. Bring a globe, a flat map, and a ...
Michael Hall's user avatar
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69 votes
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Is the destination of a commercial flight important for the pilot?

The pilots in this case did know where they were going: Edinburgh. BA said a paperwork error was to blame, with the pilot following orders from Germany, where WDL’s head office had filed the ...
StephenS's user avatar
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58 votes

How did the 9/11 hijackers find their way to New York City?

All of the hijacked flights were going in different directions and had to be piloted to a different destination. The hijacker pilots had different degrees of success in doing this. The flight paths ...
Tyler Durden's user avatar
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51 votes

Why don’t airplanes use turn signals?

I think the points raised in other answers are good, but they miss the essential difference. Cars choose from a discrete set of options, but planes do not. When you indicate left when driving you are ...
Jack Aidley's user avatar
48 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 ...
mins's user avatar
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44 votes
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Why does IRS alignment take so much time?

GPS faster? Yes and no GPS is faster depends on which case we want to consider: Cold start, restart or operational use. Cold start, like for example the first time we use the instrument: Inertial ...
mins's user avatar
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39 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 ...
mins's user avatar
  • 74.5k
36 votes

Do today's aircraft still have INS (inertial navigation system)?

Short answer Aircraft still use inertial navigation systems because INS is autonomous, it doesn't need any external support to work, it provides more information, and is more accurate than a GNSS in ...
mins's user avatar
  • 74.5k
35 votes

In the rare event that the U.S. DOD shuts off the GPS, what's the alternative?

If the GPS is unavailable, it will be quite an impact to the aviation industry. All airliners in-flight will experience degraded RNAV performance, but they would make it to the destination using VORs,...
kevin's user avatar
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34 votes

When flying VFR without GPS, how do pilots know if they are inside controlled airspace or not?

VFR aviation maps called "sectionals" (and now GPS map displays) depict the types of airspace through borders with different colors and dashed lines. You can buy or download the maps for free from ...
jwzumwalt's user avatar
  • 11.5k
34 votes

Why don't planes (mostly airliners) primarily use GPS for navigation?

Satellite-based navigation is not reliable. The operator can turn it off. The satellites can fail. The signal can be jammed or spoofed.
Anonymous Physicist's user avatar
33 votes

Can a great circle be drawn between any two points on Earth?

A great circle drawn along a sphere will, with the exception of the one drawn exactly along the equator, intersect all parallels of latitude it passes by exactly twice. To make it intersect any two ...
Jpe61's user avatar
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33 votes
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Can a great circle be drawn between any two points on Earth?

I believe you are having trouble imagining it because you are allowing the smaller circles formed by the lines of latitude themselves to constrain your thinking. Consider two points at roughly 45 ...
Michael Hall's user avatar
  • 26.5k
28 votes

Why might this trans-pacific flight not follow a more direct route?

Looks like they were avoiding a storm system from Oregon north into Canada.
TomMcW's user avatar
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27 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 ...
mins's user avatar
  • 74.5k
27 votes

Can astronavigation be used during flight?

You sure can! It's not really done all too much any more in the days of GPS but it was done quite a bit in the early days of aviation. Historically, this was done by the "flight navigator" a position ...
Dave's user avatar
  • 101k
25 votes
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Do airlines use GPS for critical purposes? If so, why?

GPS, or to be more accurate, GNSS is a commonly used navigational aid in aviation, especially in smaller passenger planes. Larger airliners are more likely to be also equipped with inertial navigation ...
Jpe61's user avatar
  • 28.9k
24 votes

Can a great circle be drawn between any two points on Earth?

The shortest path between any two point on a sphere follows a great circle. There is exactly one great circle for any pair of two non-identical points on the surface of a sphere, unless they are ...
Federico's user avatar
  • 32.6k
23 votes

What's the minimum number of sensors for a hobby GPS waypoint-following UAV?

The absolute minimum for a generalized vehicle that needs to know its position and attitude (orientation) in space is one per degree of freedom. This can be reduced if we have information about the ...
AEhere supports Monica's user avatar
23 votes

How do missiles navigate and determine their orientation without GPS?

As per comments, this question is referring to guided weapons such as Stinger (IR guidance). Guided missiles that acquire their target via signal return, such as infrared, radar or laser designation (...
Jpe61's user avatar
  • 28.9k
23 votes

How were compasses in early interwar planes safeguarded against interference from flight?

The unreliability is caused by the nearness of several big bits of magnetic material, chiefly an engine, and some electrical equipment. The countermeasures are something called "swinging the ...
DJClayworth's user avatar
  • 4,502
22 votes
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What is the purpose of a Victor Airway?

An airway (Victor or otherwise) is just a standard route for aircraft to fly on in the national airspace system - for all practical purposes they are literally highways in the sky (with the lanes ...
voretaq7's user avatar
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