Ask A Scientist© Engineering Archive

Index Key:   ENG006
Author:      katie
Subject:     Flight navigation.
How can a pilot tell where he has going if all he can see is clouds?

Response #:  1 of 1
Author:      david r munoz
Hi Katie:
You have asked an interesting question.  There are several ways that a pilot
can tell which way he/she is going.  First of all, he could use a compass,
which uses the magnetic field of the earth to determine direction.  However,
the compass is not really used by pilots now days, besides it would be
difficult to use a compass if you were flying over the north or south poles
(basically it would be useless).  Pilots now days use satellites that orbit
the earth and devices called geographical positioning systems (GPS).  These
GPS devices will use three different satellites to determine position with a
technique called triangulation.  The satellites emit a signal that the GPS
can receive to determine its position relative to the satellite.  If at
least two satellites are used and sometimes even three are used, the
position of the aircraft can be determined relative to the earth.  The
output from the GPS will be a coordinate in longitude and latitude on the
earth's surface.  These GPS systems are also used to determine the plane's
speed because it also contains a clock.  If you know the position change and
the elapsed time then you can calculate the speed by dividing the distance
covered by the elapsed time.