Communications, navigation and surveillance (CNS) requirements and procedures
Communication, navigation and surveillance
CNS requirements depend on the airspace and operation. VHF radio is the normal means of communication in controlled airspace; HF may be required on remote routes. Navigation equipment must be suitable for the route and approach, whether GNSS, VOR, NDB or another approved system. Surveillance may involve radar, secondary surveillance radar transponders or ADS-B, and the pilot must operate and monitor the equipment as required.
Procedures
Pilots must use correct phraseology, read back clearances, maintain a listening watch and follow lost-communication procedures. Before relying on GNSS, confirm database validity, receiver autonomy and approach approval. Transponder codes such as 7600 (radio failure), 7700 (emergency) and 7500 (unlawful interference) are internationally recognised, but they do not replace a distress call when communication is possible.
Worked example
An IFR aircraft loses VHF communication in controlled airspace. The pilot squawks 7600, continues according to the last acknowledged clearance or the published lost-communication procedure, and attempts contact on other available means. Climbing or descending without a clearance because “the radio failed” is not automatically permitted; the procedure and airspace must be considered.
Traps
A transponder is not a substitute for a clearance. A GNSS moving-map display is not automatically an approved navigation source for an instrument approach. Do not leave a listening watch because the frequency is quiet.