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 ...
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92 votes
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What are the differences between Bearing vs Course vs Direction vs Heading vs Track?

This is how I explain it! Heading: This is where my nose points - and seeing as my nose is attached to my head, this is where my head (and thus my machine) is pointing relative to north. Course: This ...
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  • 1,186
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. ...
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  • 26k
79 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 (...
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  • 44.5k
77 votes
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How can pilots fly inside a cloud?

When aircraft fly inside clouds, they fly under "instrument rules". It doesn't matter whether the visibility is reduced (at night) or totally blocked (in a thick cloud), this mode of flying ...
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  • 67.7k
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 ...
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  • 16.3k
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 ...
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  • 26k
65 votes
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Why do pilots use airways instead of just "flying direct" every time?

Airways simply allow for better management of traffic. Imagine for a moment that everyone had an off-road capable car, if all the drivers were going "GPS Direct" to their destination how would drivers ...
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  • 15.5k
64 votes
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Where do I land if I fly from KLAX with a constant east heading, crossing the US and the Atlantic ocean?

If an aircraft is following a magnetic course changes in magnetic declination as the aircraft moves along its route of flight will affect the true course, and on a long flight such as the hypothetical ...
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  • 7,147
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 ...
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53 votes

Do pilots need to know how to use a sextant?

Ooh, a celestial navigation question...about airplanes... I never thought I'd see one of these in the 21st century! To answer the basic question: Pilot training doesn't cover sextant use, but there ...
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  • 67.2k
52 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 ...
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43 votes
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Do pilots need to know how to use a sextant?

Can a sextant be used while flying? Yes it can. Some aircraft like 747 for example had a sextant port to allow celestial navigation. How accurate/reliable is a sextant, both standing still and at ...
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43 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 ...
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  • 67.7k
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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  • 67.7k
39 votes
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Why does "no aircraft cross directly over the pole"?

This article from AA (titled "Over the Top" by Gerard J. Arpey) says, By the way, because of the limitations of older navigation systems, none of the polar routes we fly crosses exactly over the ...
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  • 3,064
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 ...
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  • 67.7k
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,...
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  • 39.2k
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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  • 67.7k
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 ...
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  • 11.2k
32 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 ...
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  • 20.8k
32 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 ...
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  • 16.3k
30 votes
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What will happen if satellite navigation fails?

It only takes 3 satellites for a GPS fix (4 if you want altitude). There are 31 operational satellites currently in orbit and at any given time you can most likely receive a signal from half a dozen ...
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  • 96k
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.
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  • 27.5k
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 ...
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  • 96k
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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  • 67.7k
24 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 ...
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  • 20.8k
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 ...
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