Transponder Failure at the Class C Boundary
You are flying a Cessna 172 VFR from a private strip to a coastal international airport whose control zone is Class C. Before departure you file a flight plan and receive a squawk. Twenty minutes out, at 2,500 ft AMSL, the transponder display goes blank and the unit will not respond to any mode selection; Mode C is also lost. You are 25 nm from the zone boundary with 2 hours 10 minutes of fuel, 45 minutes of which is your planned reserve. Visibility is 15 km, cloud base 5,000 ft, and the terrain is flat. You call Approach 15 nm before the boundary and request entry. The controller replies: 'A6-ABC, remain outside controlled airspace, standby.' Two minutes later the frequency is busy and you have not received a further clearance. You are now 8 nm from the boundary and closing.
1. Are you cleared to enter Class C? What does 'remain outside, standby' mean?
Read the worked answer
No. 'Remain outside controlled airspace, standby' is not a clearance. In Class C, VFR flight requires an explicit ATC clearance; 'standby' only means wait. The transponder failure does not authorise entry either.
You must stay outside the boundary and be positively cleared before entering. A busy frequency and a closing distance do not create an implied clearance.
2. What should you transmit, and what are your options if no clearance arrives by the boundary?
Read the worked answer
Transmit: 'Approach, A6-ABC, 8 nm southwest, 2,500 ft, transponder failure, request clearance to enter controlled airspace or instructions.'
If no clearance arrives, turn away from the boundary and remain in Class G; hold clear or divert to an uncontrolled aerodrome. You have 2 hours 10 minutes of fuel with a 45-minute reserve, so there is no immediate emergency. Do not squawk 7600: that is the radio-failure code, and your transponder is unserviceable anyway. If ATC later offers a clearance, clarify how they will identify you without a transponder.
3. If the radio then fails completely while you are still outside the zone, what do you do?
Read the worked answer
Remain VMC and outside controlled airspace, land at the nearest suitable aerodrome, and telephone ATC afterwards.
If you were already inside Class C when the radio failed, follow the VFR lost-communication procedure: continue VMC, land at the nearest suitable aerodrome and notify ATC. Do not enter Class C without a clearance merely because the radio failed; if safety requires entry, declare an emergency and do only what is necessary.