How does aircraft navigation work?

PedroMorgan
  • How does aircraft navigation work? PedroMorgan

    Is it possible to briefly summarize how a commercial plane navigation system operates to a layperson (e.g. a passenger)?

    The aircraft takes off, reaches a certain altitude, and then lands perfect on a runway somewhere else.

    How does the navigation system affect this?

    How do pilots know where to go and where to land?

  • How do you navigate in your car?

    Before you depart, you have a general understanding of which direction you're going.
    (the supermarket is to the east of my house, about 3 miles. I believe it will take me about 5 minutes to get there).

    When you start driving, you keep your eyes open looking for information and clues.
    (The yellow lines on the road denote a two-way street. Certain landmarks are familiar and expected.)

    As you proceed, you may refer to your car dashboard to make sure things are as expected
    (My speed is 43MPH. I had planned for 45MPH... pretty close. My engine is running at 2,500 RPM, which is appropriate)

    You may have advanced instruments as well
    (The GPS in my car is telling me to take the next right turn, and go 1/2 mile)


    Its very much the same with flying.

    Pilots have pre-flight preparation where they go over a general plan.
    (we're going to fly north, on a heading of about 025 for 3 hours. We'll be passing over a large lake, and landing at our destination with a city off to our left)

    As they move towards the runway, they look for other airplanes, read the signs around the runway, and refer to their maps.
    (I see a sign indicating I'm on taxi-way Bravo, approaching Runway 31. I see yellow markings on the pavement indicating I should get permission before I cross)

    Once they take off, they look at their instruments to verify they're going at the expected speed, altitude and direction.
    (Altitude is 35,000 feet, as planned. Engines are at the right pressure, and speed is 440 knots, as expected)

    They can look out the window for large landmarks, lakes, mountains, cities, etc.
    (I'm passing by the mountain I saw on the map. I see the river valley below me, and a large city ahead of me, just like I planned)

    They may use advanced services like GPS Navigation, Radar and radio signals to help navigate. (My GPS is showing my position and direction. It says to turn a little to the right to stay on course. The navigation radio says I'm 25 Nautical Miles away from the radio transmitter)

    And they can talk to Air Traffic Control who can observe them on radar, and advise them to make adjustments to their course for navigation, and to stay separated from other airplanes.


    If they cannot see out the window, navigation does become a bit more complicated, and reliant on Instruments, GPS, Radar and Radio.

    But given a very careful plan of "Fly for exactly 31 minutes, at exactly a heading of 027, at exactly a speed of 130Kts", it is pretty remarkable how close the airplane will end up to the intended destination.

    That process is called Dead Reckoning. It requires some detailed advanced planning, but isn't that difficult. Combining Dead Reckoning with Instrument flying, and pilots can go through zero-visibility and still come out at the intended location.

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