Q-Codes (QNH, QFE, QDR, QDM)

Q-Codes are standardized three-letter abbreviations originally developed for Morse code transmissions. In aviation, a limited set of Q-Codes remains in common use, primarily in radiotelephony and navigation. They allow concise communication of technical information between pilots and air traffic services.

The four most relevant Q-Codes in modern aviation are: QNH, QFE, QDR, and QDM.

• When set on the altimeter, QNH causes the instrument to display altitude above mean sea level
• Used during takeoff, landing, and low-level enroute operations
• Provided by ATC or ATIS in hectopascal (hPa) or millibars (mb)

• “QNH one zero one five”
• “Set QNH, indicating 1,200 feet”

• When set, QFE causes the altimeter to read zero on the ground at a specific airfield
• Altimeter then shows height above ground level (AGL)
• Still used in gliding, military operations, and occasionally in training
• Not used in IFR or international operations

• “QFE one zero zero five, indicating zero on apron”
• “Maintain 1000 feet QFE”

• Indicates the magnetic bearing from a radio navigation station to the aircraft
• Used for position reporting, direction finding, or tracking outbound from a VOR/NDB

• “Your QDR is 270 degrees” → Aircraft is west of the station
• “Report passing QDR 090 from LIN VOR”

• Indicates the magnetic heading to a radio station (with no wind correction)
• Used for steering or for pilot request of vectors or navigation assistance
• Also provided by ATC with Direction Finding (DF) equipment

• “Request QDM to VOR”
• “QDM 120, steer heading 120 to reach station”

• “QNH one zero one eight, set and crosscheck”
• “QFE one zero zero four, indicating zero”
• “QDM 090 to station, steer heading 090”
• “QDR 180, you are north of the VOR”

Although many other Q-Codes exist (e.g., QSY, QTE, QFU), only a small core remains in practical aviation use today — especially in voice communication and low-tech navigation scenarios.