Mandatory Broadcast Zone With a Failing Radio
You are inbound VFR to a non-controlled aerodrome that lies within a mandatory broadcast zone (MBZ). You are 5 nm south at 1,500 ft, joining for runway 23. The aerodrome has a published circuit direction and a glider operation on the north side. Another aircraft calls 'downwind' as you call '5 nm south, joining overhead'. A third aircraft calls 'final' while you are on base. Your radio becomes intermittent and you can transmit but not receive reliably. There is no control tower. The weather is fine and the circuit is busy with three other aircraft. You must decide how to join, what calls to make, and who has right of way. You also need to consider what to do if the radio fails completely before landing.
1. What are the MBZ radio requirements and what calls should you make?
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An MBZ requires a serviceable radio and mandatory position calls. You should make standard calls: '5 nm south, joining overhead runway 23', then downwind, base and final. Listen out on the MBZ frequency, and keep calls concise. If the radio becomes intermittent, treat it as a failure for MBZ purposes: do not continue into the MBZ relying on a radio you cannot receive. Divert to an aerodrome outside the MBZ or hold clear and try to restore the radio. Do not enter and hope; other traffic will be relying on your calls.
The purpose of the MBZ is to ensure all traffic is on the same frequency and aware of each other. A radio that can transmit but not receive is not serviceable for that purpose. The safe decision is to stay clear until communications are restored or to divert.
2. Who has right of way between you on base and the aircraft on final?
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The aircraft on final has right of way over you on base. You should give way: extend downwind, slow down, or go around. If you are both on final, the lower aircraft normally has right of way, but landing aircraft have priority and you must avoid cutting in front. Gliders have right of way over powered aircraft, so avoid the glider area. The decision should be made early and communicated: 'Cessna on base, giving way to the aircraft on final'.
Right-of-way rules do not remove the need to see and avoid. Even if you have priority, you must not force another aircraft to take evasive action. In a busy circuit, the safest action is often to go around and rejoin rather than squeeze in.
3. What planning documents and in-flight decisions would you use?
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Before flight, check AIP NZ aerodrome and MBZ entries, NOTAMs, circuit direction, runway data, frequencies, glider activity, and weather. In flight, monitor the radio and use the standard calls. If radio failure occurs, leave the MBZ and divert. Also consider the traffic density and your own experience; if the circuit is busy and your radio is unreliable, the safest option is to land elsewhere and fix the radio. The aim is to avoid a mid-air collision and to comply with the MBZ rule.
Planning should include an alternate aerodrome outside the MBZ and a personal minimum for radio serviceability. In-flight, use a sterile-cockpit approach in the circuit and communicate intentions clearly. If you cannot receive, assume other traffic cannot rely on your calls and act accordingly.