In aviation radiotelephony, Type C call signs are the most widely used format in commercial operations. These call signs consist of:
- The telephony designator of the aircraft operating agency, followed by
- The flight identification number
Typical Examples
- SCANDINAVIAN 937
- Fastair 345
- AIC 111 → “Air India One One One”
- IGO 2234 → “IndiGo Two Two Three Four”
- SEJ 2034 → “SpiceJet Two Zero Three Four”
Standard ICAO Rule (Core Principle)
As per ICAO provisions, Type C call signs shall always be transmitted in full.
There is no provision for abbreviation.
This rule exists to:
- Prevent call sign confusion
- Enhance situational awareness in high-density traffic
- Maintain standardization in global operations
Use of Alphanumeric Call Signs
With increasing traffic and call sign similarity issues, operators are now adopting alphanumeric call signs, including combinations of numbers and letters.
Example
- HIGHJET 12BA
Correct RT Transmission
- “HIGHJET, WUN TOO, BRAVO ALFA”
Incorrect (Not Permitted)
- “HIGHJET BRAVO ALFA” ❌
Key Point
Even when letters are used at the end (bi-grams), the entire call sign must be transmitted, including numeric components.
Exception to the Rule – France
In practice, a notable exception exists:
In France, under a national regulatory framework:
- Controllers may abbreviate Type C call signs
- This applies only when the call sign ends with a two-letter bi-gram
Example
- HIGHJET 12BA → may be shortened to HIGHJET BRAVO ALFA (France only)
Important Limitation
This exception does NOT apply to:
- HIGHJET 3456
- HIGHJET 345B
Operational Trend
The use of final two-letter bi-grams is increasing because:
- It helps in call sign similarity deconfliction
- Reduces confusion between similar numeric call signs
- Improves identification in congested airspace
Operational Advisory (Industry Practice)
Air Navigation Service Providers (ANSPs) and aircraft operators are encouraged to:
- Share operational practices for managing call sign confusion
- Improve:
- Sector and frequency management
- Monitoring procedures
- Flight Data Processing (FDP) and HMI track labeling
- Ensure availability of proper R/T designators to controllers
- Promote the use of alphanumeric call signs where appropriate
Regulatory Emphasis (ICAO Compliance)
Controllers and flight crews must be reminded that:
- Type C call signs consist of:
- ICAO R/T designator (not the 3-letter code), and
- Flight identification
- Abbreviation is not permitted, except for the France-specific case
Recommendation for Operators
Aircraft operators should:
- Apply for an official ICAO R/T designator in accordance with ICAO Doc 8585 (if not already assigned)
- Adopt standardized call sign formats to enhance safety and communication clarity
Final Exam-Oriented Takeaway
- Type C = Operator + Flight Number
- No abbreviation allowed (standard ICAO rule)
- Exception: France (only for final two-letter bi-grams)
- Increasing use of alphanumeric call signs for deconfliction
