Aircraft callsign

Aircraft Call Signs

Call signs uniquely identify an aircraft on the radio. They are based on the registration mark per ICAO Annex 7.

Source: ICAO Annex 7 Aircraft Nationality and Registration Marks; ICAO Doc 9432 Chapter 2.

Registration structure

Format: state prefix + registration suffix

German sub-classes (for D-...):

• D-E... = single-engine aeroplanes < 2000 kg.
• D-K... = motor gliders.
• D-A... = multi-engine > 5.7 t (heavy traffic).
• D-I... = twin < 5.7 t.
• D-G... / D-M... = gliders.

Full call sign

Spelled in full: "Delta Echo Mike Romeo Alpha"

Phonetic spelling:

• D = Delta
• E = Echo
• M = Mike
• R = Romeo
• A = Alpha

Abbreviated call sign

After first contact with ATC, the call sign may be abbreviated, but only after ATC abbreviates first.

Rule (ICAO Annex 10):

• Pilot uses full call sign on first contact.
• ATC may abbreviate, e.g. "Mike Romeo Alpha" or "Romeo Alpha" for DEMRA.
• Pilot may then also abbreviate, only if ATC does so.

Important: if the pilot abbreviates earlier than ATC, confusion may arise with other similarly-named aircraft.

Germany-specific abbreviation rule

In German airspace a standardised abbreviation form for German registrations is common:

Format: "D" + the last 2 characters of the call sign.

→ ATC uses this form once it is clear after the initial call that there is no confusion risk with other aircraft.

Example initial call full:

• Pilot: "Frankfurt Tower, Delta Echo Foxtrot Echo Foxtrot, request taxi."

Example ATC reply with abbreviation:

• ATC: "Delta Echo Foxtrot, taxi via Alpha to runway 25."

Example pilot read-back abbreviated:

• Pilot: "Taxi via Alpha runway 25, Delta Echo Foxtrot."

Pilot must NOT change the call sign

Important rule:

• The call sign of an airborne radio station must NOT be changed by the pilot during the flight.
• A change is only permissible if the ground station (ATC) explicitly assigns a different call sign to avoid confusion.

Classic scenario: two aircraft with very similar call signs on the same frequency (e.g. D-EMRA and D-EMRB). ATC assigns one of them a temporary call sign:

• ATC: "DEMRA, for the duration of this flight, you are Alpha Sierra One."
• Pilot: "Roger, Alpha Sierra One."

Until the flight ends the pilot then uses the new call sign.

→ Pilot cannot decide this themselves — only the ground station.

Commercial call signs

Airline flights use operator callsign + flight number:

• Lufthansa 123 ("Lufthansa One Two Three").
• Swiss 247 ("Swiss Two Four Seven").
• British Airways 789 ("Speedbird Seven Eight Niner" — "Speedbird" is the ICAO operator callsign for BA).

The ICAO operator callsign (3-letter code) is listed in ICAO Doc 8585 Designators for Aircraft Operating Agencies:

• DLH (Lufthansa): "Lufthansa"
• SWR (Swiss): "Swiss"
• BAW (British Airways): "Speedbird"
• AFR (Air France): "Airfrans"

Private vs commercial call signs

Standard phrases on similar call signs

When ATC has two similar callsigns (e.g. DEMRA and DEMRB):

• ATC requires full pronunciation of both callsigns on every transmission.
• "Like-sounding callsigns" → pilot stays attentive.
• Possibly ATC assigns a temporary callsign (see above).

Call sign accommodation to traffic

ICAO recommends for any sector / FIR to use callsigns with all positions when:

• High traffic.
• Multiple aircraft with similar callsigns on frequency.
• Non-native pilot in local language.

Practical practice

• Own callsign flowing pronunciation (both full and abbreviated).
• Instructor mock radio in training.
• In large TMAs: ATC may call several times per minute → callsign must be recognised reflexively.