QDM

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DFS VDF direction finder on the Deister near Hanover

The term QDM comes from radio navigation and in aviation refers to the magnetic direction finding from an aircraft to a ground transmitter. However, the letters QDM have no direct meaning. Question Direction Magnetic can, however, be noted as a donkey bridge. The abbreviation QDM comes from the times of the Morse code, which has survived to this day ( Q key ).

Drawing of a QDM

There are several ways to get the QDM to a station.

At a workstation of an air traffic control controller and at some airports without an air traffic control service, the QDM is determined using VDF and UDF direction finders. A special antenna determines from which direction the radio signal is coming during the radio conversation with the aircraft. The radar software shows this bearing as a line in the radar image so that the air traffic controller can recognize which aircraft he is talking to. At smaller airports, the bearing result is displayed on a separate device and communicated to the pilot via radio. However, this type of QDM determination is becoming less and less important.

The pilot can also determine the QDM for a station himself. The course to a transmitter can be calculated from the addition of missweisendem heading ( English magnetic heading, MH ) and the relative Seitenpeilung (English relative bearing, RB ). This relative bearing is determined with the on-board ADF direction finder. Modern display devices such as the RMI - Radio Magnetic Indicator - also display the QDM directly without the pilot having to calculate the heading MH and the lateral bearing RB in his head.

With the on-board VOR (Very High Frequency Omnidirectional Radio Range), the QDM can be displayed directly for a corresponding ground station.

Modern navigation systems enable the pilot to determine the QDM for practically any navigation point on the earth's surface.

QDM = MH + RB

The QDR is the reverse of the QDM. If there are two QDRs from different stations, the pilot can take a cross bearing to determine the current position during the flight. In order to be able to draw these magnetic bearings on a map, the QDR must first be converted into the so-called QTE by taking into account the location misalignment . This is the true bearing from the station to the aircraft.

Exemplary calculation of the QDM:

Given: MH 123 °, RB 043 °

Wanted: QDM, QDR

Solution:

QDM = 123 ° + 043 ° = 166 °
QDR = 166 ° + 180 ° = 346 °

See also

literature