Transponder Failure En Route to Controlled Airspace
You are flying a Cessna 172 VFR from Masterton to Wellington, a Class C controlled aerodrome. The aircraft has a serviceable Mode A/C transponder at departure. About 30 nm north of Wellington, at 2,500 ft AMSL, the transponder fails; the radio still works. The weather is fine: visibility 20 km, cloud base 4,000 ft, and you are in Class G airspace. You have not yet entered Class C. You call Wellington Approach, advise the transponder failure, and request clearance to enter controlled airspace and land. The controller says she will check traffic. You are conscious that Wellington is a busy controlled aerodrome and that your aircraft is now non-compliant with the transponder requirement. You have 1.5 hours of fuel remaining and the weather is not deteriorating. You need to decide whether to hold outside, divert to an uncontrolled aerodrome, or accept a clearance if offered.
1. May you enter Class C without a serviceable transponder? What factors determine the answer?
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A clearance into Class C is required, and controlled airspace in New Zealand also carries an equipment expectation, including a serviceable transponder. You should not treat the clearance request as permission. Until the controller explicitly clears you, you remain outside Class C and in Class G. The controller may be able to provide a clearance and separation with the transponder failed, but that is an ATC decision based on traffic, radar coverage and workload. Advise the failure clearly, state your position, altitude and intentions, and ask whether she can accept you. If she cannot, remain clear. Do not enter on the assumption that 'the radio still works' or that the failure is minor. The legal test is compliance with the clearance and the applicable equipment rule; the safety test is collision avoidance in busy terminal airspace.
2. What are your lawful and safe options if ATC is unable to approve entry?
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Options include holding outside the boundary at a safe altitude and distance while ATC checks traffic; requesting a clearance to a VFR reporting point outside Class C and awaiting further; diverting to an uncontrolled aerodrome where the transponder can be repaired; or returning to Masterton. Consider fuel (1.5 hours remaining), weather, passenger comfort and the possibility that ATC may become able to accept you. Do not orbit in a way that conflicts with the arrival path. If you divert, make a positive decision early rather than pressing on. If ATC offers a clearance, confirm the conditions and read back the clearance. If the radio later fails, squawk 7600 and follow the lost-communication procedure, but that is separate from the transponder failure.
3. What pre-flight and in-flight responsibilities does this event illustrate?
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Pre-flight, you should check aircraft equipment, maintenance status, transponder inspection and alternate routes. Check AIP, NOTAMs and controlled airspace boundaries, and plan an alternate that avoids controlled airspace if equipment is doubtful. In flight, monitor the radio, advise ATC early, use standard phraseology, and make a decision under pressure. The event illustrates that a clearance is not a right and that equipment serviceability affects the routes available to you. It also shows the value of carrying enough fuel to divert and of telling ATC about a failure before reaching the boundary. If the event affected safety, consider filing an occurrence report so that the equipment problem is recorded and investigated.