VHF Direction Finder (VDF)-Procedures

A pilot may request a VDF bearing using the appropriate phrase or Q-Code to specify the service required (see Figure 6.1):

‘QDM QDM QDM OXFORD APPROACH G-DS REQUEST QDM, G-DS’

Figure 6.1 QDM/QDR/QTE.
Figure 6.1 QDM/QDR/QTE.

A VDF station will provide the following as requested:

• QDR: Aircraft’s Magnetic Bearing from the station (Radial); used for en route navigation
• QDM: Aircraft’s Magnetic Heading to steer (assuming no wind) to reach the VDF station; used mainly for station homing and let-downs using published procedures
• QTE: Aircraft’s True Bearing from the station; used for en route navigation
• QUJ: Aircraft’s True Track to the station; not generally used

Note: QDM is the reciprocal of QDR; QUJ is the reciprocal of QTE. QDR, QDM and QTE are most commonly used.

The direction-finding station will reply in the following manner:
• The appropriate phrase or Q code
• The bearing or heading in degrees in relation to the direction finding station
• The class of bearing
• The time of observation, if required

The accuracy of the observation is classified as follows:
• Class A – Accurate within ± 2°
• Class B – Accurate within ± 5°
• Class C – Accurate within ± 10°
• Class D – Accuracy less than Class C

Note: Normally, bearings no better than Class B will be available. The latest equipment uses Doppler principles to determine a high-resolution bearing that can be displayed as a digital read-out; bearings produced in this manner have an accuracy of ±0.5° (available on UHF and VHF systems).

Behnam Bidar

Commercial Pilot Of I.R.I And The Civil Aviation Training Group Supervisor

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VHF Direction Finder (VDF)-Procedures

by Behnam Bidar time to read: 1 min
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