VFR Clearance Limit and Radio Failure at a Controlled Aerodrome
You are pilot-in-command of a Cessna 172 on a VFR flight from Almaty (UAAA) to Taldykorgan. Cruising at 7,500 ft with QNH 1018 hPa, you request entry into Class C airspace. ATC clears you: "Via A-343, maintain 7,500 ft, squawk 6042, report 10 nm before Taldykorgan." You read back correctly. Twelve nautical miles after entering the airway, the COM radio fails: you can neither transmit nor receive. The weather is VMC with cloud base 4,500 ft and visibility 20 km. Your transponder still works, and you have no handheld radio. Taldykorgan is a controlled aerodrome with a tower; the destination QNH is 1016 hPa. Your clearance limit is Taldykorgan, no alternate is specified, and fuel endurance remaining is 2 h 30 min. You must decide what to do before reaching the control zone.
1. What are your immediate actions after the radio failure, including transponder and altitude management?
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First maintain aircraft control and continue VFR at 7,500 ft, because the clearance has not been cancelled and VMC exists. Set the transponder to 7600 to signal radio failure; if the unit has an ident feature, do not use it unless requested. Try the second COM radio, check headset plugs, squelch, volume and the relevant circuit breaker, but do not troubleshoot for long. Keep a listening watch on the last assigned frequency and, if available, the destination tower frequency in case reception returns. Because you are already cleared into Class C via A-343, remain on the cleared route and altitude rather than deviating into other controlled airspace. Do not climb into cloud or enter IMC. Prepare to use light signals at Taldykorgan. If fuel or weather deteriorates before the control zone, divert to an uncontrolled aerodrome and land, then telephone ATC.
2. May you continue into the Taldykorgan control zone and land? Explain the light-signal procedure and the conditions under which you must divert.
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You may continue toward Taldykorgan because you are VFR and already hold a clearance along A-343 to the aerodrome, but entry into the control zone and landing require ATC clearance. With a receiver failure, you cannot obtain a voice clearance, so you must look for light signals from the tower. A steady green light means cleared to land; a flashing green means return for landing; a steady red means give way and continue circling; a flashing red means the aerodrome is unsafe and you must not land. If you receive a steady green, land normally and report the failure to ATC after vacating. If you receive no signal, or a red signal, remain clear of the control zone and divert to a suitable uncontrolled aerodrome. Do not assume that the original airway clearance authorises landing. Because VMC is good, orbiting outside the zone while awaiting signals is acceptable, but fuel reserves must be protected.
3. How should you manage altimeter settings en route and at destination, and what altimeter error matters in this scenario?
Read the worked answer
Below the transition altitude, keep the altimeter set to the current QNH. En route you have 1018 hPa; when approaching Taldykorgan, obtain the destination QNH of 1016 hPa from ATIS or the tower before entering the control zone. The 2 hPa difference is about 60 ft: setting 1016 instead of 1018 makes the indicated altitude slightly lower for the same pressure altitude, so you must not delay the change until after crossing the zone boundary. If no ATIS is received because of the radio failure, use the last known QNH and add a conservative margin over the minimum safe altitude. Do not use the standard 1013 hPa setting for VFR cruising below the transition altitude. At destination, if a light signal clears you to land, land and report the actual QNH used; this helps ATC identify any altitude deviation.