Readback Accepted: A 300 m Level Error in Class C Followed by Transmitter Failure
You are the pilot-in-command of a Cessna 172 departing Boraldai, near Almaty, on a VFR flight north through the Almaty TMA, which is Class C airspace. The tower clears you: “Climb to 1,200 metres, QNH 1014 hectopascals, squawk 6042, report leaving the control zone.” You read back “climb 1,500 metres, squawk 6042” and the controller answers “readback correct”. You climb through 1,350 metres. A departure controller then clears a Boeing 737 to cross your area at 1,400 metres, and your traffic awareness is limited to the radio. At that moment your VHF transmitter fails: you can hear ATC and other aircraft perfectly, but nothing you transmit is acknowledged. The weather is CAVOK, visibility over 20 km, cloudbase above 3,000 metres, and you have 2 h 40 min of fuel for a planned 1 h 20 min flight. The transponder is serviceable.
1. The controller answered “readback correct” to your wrong level. Who carries the responsibility for the resulting conflict risk, and what must you do in the next 30 seconds?
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Responsibility is shared, but the clearance that must be flown is the one ATC issued - 1,200 m - not the one you read back. Under ICAO Annex 2 and PANS-ATM the pilot must read back safety-related clearances correctly, and “readback correct” is a confirmation, not a new clearance; because neither side caught the mismatch, the pilot is expected to notice it against the original transmission and query it. You did not, and the controller did not hear it.
Immediately: stop the climb, descend back to 1,200 m, level off, and turn clear of the 737's crossing track while remaining VMC. Do not climb to 1,500 m to “get above” anyone. Your transmitter has failed, so you cannot clarify by RT; the only safe assumption is that ATC is separating traffic from an aircraft at 1,200 m and that any other level makes you an unknown. A 300 m error at these levels is far outside standard separation and is exactly the altitude-bust chain the exam expects you to break early.
2. State your radio-failure actions, including the SSR code, and explain whether you continue to destination.
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Squawk 7600 and leave it there. Continue in VMC, keep the assigned altimeter setting and 1,200 m, and stay clear of controlled airspace you are not cleared for. Standard VFR practice is to continue under VMC, land at the nearest suitable aerodrome - Boraldai behind you, or the first aerodrome with an operating ATS - and report arrival to ATS, normally by telephone, so the controller can close the flight plan and stand down any alert.
Continuing to destination is wrong for three reasons: ATC already has an unresolved traffic situation created by your wrong level; your “report leaving the control zone” call will never come and will trigger the controller's own contingency actions; and a 1 h 20 min planned flight leaves ample fuel to divert but no reason to press on. Because your receiver works, watch for light signals: steady green = cleared to land; steady red = give way and continue circling; flashing red = aerodrome unsafe, do not land; flashing green = return for landing.
3. After landing, what must you do, and what makes this a reportable occurrence rather than a routine radio failure?
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Telephone the ATS unit, identify yourself by callsign, state the time and place of the failure, the level actually flown, the transponder code selected and the landing time, so the controller can close the flight plan and cancel any uncertainty phase. Then file a mandatory occurrence report with the civil aviation authority.
This is not just a radio failure. The chain contains an incorrect readback that was accepted, an undetected 300 m level error, a commercial aircraft cleared to cross at 1,400 m on that assumption, and a subsequent loss of communication - any one of which is reportable, and together they are an airprox risk. Record the original clearance, your readback, the controller's reply and the time the transmitter failed, and ask ATC whether the transponder should stay on. Do not treat the event as closed because you landed safely: the reporting system exists to fix both the unit's monitoring and your own readback discipline.