Q Codes (QNH, QFE, QDM, QDR)

Where Q codes come from

Q codes were created in the early 1900s for Morse code communications between naval and aeronautical stations. The idea was brilliant: instead of transmitting long phrases by hand, common concepts were encoded as three letters starting with Q.

• "What is your position?" → QTH
• "What is the atmospheric pressure at sea level?" → QNH
• "What is your magnetic bearing to me?" → QDM

When radiotelephony replaced Morse, most Q codes were abandoned. But some remained because they were briefer and less ambiguous than the corresponding English phrases. Today an Italian controller can say "QNH 1018" to a German pilot with no language ambiguity — the Q code is universal.

The four Q codes you meet on every VFR flight

In a VFR flight you essentially encounter four: QNH, QFE, QDM, QDR. Others exist (QTE, QGE, QTH...) but today they're rare or restricted to specific contexts.

QNH — Station pressure corrected to mean sea level

QNH is atmospheric pressure at sea level, calculated from pressure measured at the airfield. When you set QNH on the altimeter, the altimeter shows actual geometric altitude (MSL) above sea level.

• If Lugano QNH (LSZA, elevation 915 ft) is 1018 hPa and you're on the ground, your altimeter set to 1018 will read 915 ft (the field elevation).
• If you fly to Locarno (LSZL, elevation 650 ft) and the local QNH is 1015, you must reset to 1015 — otherwise the altimeter lies.

QFE — Station pressure (at the field)

QFE is atmospheric pressure measured directly at the airfield, without correction to sea level. When you set QFE, the altimeter reads zero on the ground at the departure airport.

In Europe QFE is rare today for VFR (QNH is used). It's still found at some military airfields, in some Eastern European aeroclubs, and for training flights where the instructor wants the student to read "height above field" instead of "MSL altitude".

QDM — Magnetic bearing to the station

QDM is the magnetic heading the pilot must fly to head toward a ground station (a VOR, a direction finder, a tower). Expressed in magnetic degrees, 0° to 360°.

Example: if you're south of Lugano and ask for QDM to the Lugano VOR (LUG), the answer will be around 360° — meaning "fly toward magnetic north to reach the VOR".

QDR — Magnetic radial from the station

QDR is the opposite of QDM: it's the direction from the station to the aircraft, in magnetic degrees. If your QDM toward Lugano is 360°, then your QDR from Lugano is 180° (you're south, on radial 180).

Pronunciation of Q codes

On the radio they're pronounced letter by letter, using the ICAO alphabet:

• QNH → Quebec November Hotel
• QFE → Quebec Foxtrot Echo
• QDM → Quebec Delta Mike
• QDR → Quebec Delta Romeo

In practice though, especially between experienced controller and pilot, the accepted form is "literal" English: "Q-N-H one zero one eight". This form is universally understood.

Transition altitude and altimeter settings

In Switzerland, as in most of Europe, there's a transition altitude (TA) above which the altimeter is set to standard 1013 hPa (leaving the local QNH). This altitude is typically 7000 ft in Switzerland, but varies by country and region.

• Below TA → altimeter on QNH
• Above TA → altimeter on 1013.25 (Standard, abbreviated STD or QNE)

General VFR almost always stays below TA, so QNH is the setting you'll use 99% of the time.

Swiss specifics

Summary — to remember

1. QNH = altimeter shows MSL altitude (general VFR use).
2. QFE = altimeter shows zero on ground (military/training, rare).
3. QDM = magnetic heading TO the station.
4. QDR = magnetic direction FROM the station (radial).
5. Pronunciation: letter-by-letter ICAO, or "Q-N-H" English form.
6. Above transition altitude → 1013 hPa standard (STD/QNE).

Sources

• ICAO Doc 9432 — Manual of Radiotelephony, Chapter 5
• ICAO Doc 8400 — PANS-ABC (codes and abbreviations)
• Aero Locarno · Subject 090 — VFR Communications, Q-codes chapter
• AIP Switzerland — GEN 3.5 Meteorological Services