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

Definition

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.

QNH – Altimeter Setting for Mean Sea Level (MSL)

  • 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)
Example Phraseology:
  • “QNH one zero one five”
  • “Set QNH, indicating 1,200 feet”

QFE – Altimeter Setting for Field Elevation

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

QDR – Magnetic Bearing From the Station

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

QDM – Magnetic Heading To the Station

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

Summary Table

Q-Code Meaning Use Altimeter/NAV
QNH Altimeter shows height above MSL Standard for ATC & charts Altimeter
QFE Altimeter shows height above field Field ops, gliding Altimeter
QDR Magnetic bearing from station Position reporting, nav Navigation
QDM Magnetic heading to station Homing, nav assistance Navigation

Common Use in Phraseology

  • “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”

Note

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.