Transmitter failure after departure from a Class D control zone
You are the pilot of ZK-ABC, a Cessna 172, departing VFR from a regional aerodrome with a Class D control zone. Clearance is: 'ZK-ABC, cleared to leave the control zone via the eastern VFR route, maintain 1,500 feet, squawk 4372.' Three minutes after departure you are 4 nm east of the zone boundary, VMC, level at 1,500 feet. You can hear ATC transmissions clearly, but after two calls ATC does not reply and you hear another aircraft tell ATC that your transmissions are unreadable. You suspect your transmitter has failed; the transponder appears to be working because ATC previously identified you. You now need to return to the aerodrome because your passenger is unwell, but re-entry requires a clearance. Another aircraft on the frequency is willing to relay. You have a current NZ FRTO and must decide what to do without creating a collision or airspace risk.
1. What immediate actions should you take, including transponder code and airspace behaviour?
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Set the transponder to code 7600 to indicate a communication failure, unless ATC has already instructed 7500 or 7700. Continue VFR, remain clear of the Class D control zone and any other controlled airspace, and do not enter without a clearance. A clearance issued before the failure does not authorise re-entry after you have left the zone. Because you can hear ATC, try a relay through another aircraft. Keep a listening watch on the appropriate frequency and on 121.5 if able. Record the time the failure was confirmed and your position. Do not assume that because ATC previously identified you, your clearance remains valid. If no relay is possible, consider landing at the nearest suitable aerodrome outside controlled airspace and telephone ATS. The priority is to stay clear of controlled airspace and other traffic while you resolve the communication problem.
2. Describe how you would use a relay and what you would say, including the phraseology.
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Ask the other pilot directly: '[Callsign], ZK-ABC, request relay to ATC.' The relay aircraft should identify itself: 'Christchurch Approach, ZK-XYZ relaying for ZK-ABC.' Then pass the facts: position 4 nm east of the zone boundary, 1,500 feet VFR, transmitter failure, request re-entry clearance to land, passenger unwell. If the passenger is seriously unwell, the relay can prefix 'PAN PAN' or, if there is grave and imminent danger, 'MAYDAY'. ATC's clearance must be passed back to you and read back through the relay. Do not accept a paraphrased clearance without readback. If ATC clears you to enter, comply exactly; if ATC does not clear you, remain outside. The relay pilot should not invent or soften a clearance, and you should confirm the critical items: route, level, frequency and squawk.
3. If no relay is available and you are receiving ATC, what light signals should you expect and how should you acknowledge them?
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From ATC, airborne light signals may be used. A steady green means cleared to land; a flashing green means cleared to return for landing; a steady red means give way to other aircraft and continue circling; a flashing red means the aerodrome is unsafe and you must not land. Acknowledge by rocking the wings by day, or at night by flashing landing lights or navigation lights. If you receive no light signal and cannot establish communication, follow the lost-communication procedure: remain VFR, stay clear of controlled airspace, and land at the nearest suitable aerodrome. The light signal is a clearance only for the action it specifies; it does not authorise you to enter controlled airspace unless the signal clearly clears you to land and you can comply with the associated traffic requirements.