B.3.1 Coordinate Convention. At an airport, each runway is designated by two numbers (one
for each end). Each number designation is approximately one-tenth of the angle that
the extended runway direction makes with magnetic north. For example, depending on
its direction of use, a runway may be called Runway 4 or Runway 22. An aircraft
departing Runway 4 flies an approximate course of 40 degrees with respect to
magnetic north; similarly, an aircraft landing on Runway 4 also flies an approximate
course of 40 degrees prior to touchdown. Use of Runway 22 sets the flight course at
220 degrees with respect to magnetic north. Parallel runways receive similar numbers
with right (R) and left (L) designations.
To define aircraft crash locations relative to airfield runways and facilities, it is
necessary to establish a location coordinate system. This standard uses the Cartesian
coordinate convention with the following characteristics:
The origin of the coordinate system is at the center of the relevant runway.
The x axis coincides with the extended runway centerline; the positive direction
is the direction of flight.
The y axis is perpendicular to the x axis with the positive direction created by a
90-degree counterclockwise rotation of the positive x axis.
The coordinate system is depicted in Figure B-1.