A clearance that puts you below the minimum en-route altitude
You are the pilot of a Cessna 402C on an IFR passenger charter from Port Moresby (AYPY) to Popondetta (AYGR), off-blocks 06:40, three passengers, no airframe de-icing, and a portable oxygen system with about three hours of supply. The route crosses the Owen Stanley Ranges; cloud tops are reported at 12,000 ft and the outside air temperature at 9,000 ft is +4°C.
Clearance: 'ABC, cleared to Popondetta via W6, climb to 9,000 ft, expect 11,000 at KONDA.' You read back and enter cloud at 7,500 ft. The en-route chart shows MEA 11,200 ft from Moresby to KONDA and 8,400 ft afterwards; the area chart grid MSA is 11,200 ft. The aircraft is unpressurised. There is opposite-direction traffic at 11,000 ft, which is why the controller wants you low.
1. At the readback stage, what is your analysis of this clearance and what do you say?
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The clearance cannot be accepted as issued. The controlling minimum for the route is the MEA on the en-route chart - 11,200 ft from Moresby to KONDA - not a level chosen by ATC. A clearance is a traffic separation instruction; it does not confer terrain clearance. In IMC at 9,000 ft you would be 2,200 ft below the minimum for the most hostile part of the route over the Owen Stanleys, and the grid MSA of 11,200 ft confirms it: MSA is the emergency/off-route figure, and it is not lower.
Two further points argue for refusing early rather than querying later:
- 'Expect 11,000 at KONDA' is also below the 11,200 MEA, so the controller's whole planned profile is wrong for the terrain, not just the first level;
- at 11,200 ft the cabin is above 10,000 ft, so oxygen is required - you have it - and at +4°C in cloud with no de-icing you want to minimise time in the freezing level, which a higher level helps with.
Correct response at readback: 'UNABLE 9,000 DUE TERRAIN, REQUEST 11,200.'
2. What does 'expect 11,000 at KONDA' authorise, and what should the readback have contained?
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An 'expect' is not an authorisation. You may climb only when ATC issues the clearance; until then you stay at the last assigned level - which here is a level you should not have accepted at all.
The readback must repeat the clearance exactly as issued, and the place to correct an unacceptable level is before you read it back:
- 'CLIMB 9,000, EXPECT 11,000 AT KONDA' is an accurate readback of a clearance that is unsafe and probably unlawful to fly.
- The correct transmission is a refusal plus a request: 'UNABLE 9,000 DUE TERRAIN, REQUEST 11,200, NEGATIVE EXPECT 11,000 AT KONDA.'
The 'expect' still tells you something useful: it is not a clearance and gives no protection, but it reveals the controller's intended profile. If the expected level is also below the MEA, say so immediately, so the whole profile is renegotiated while you are still climbing near the departure aerodrome, where a hold is easy and fuel is plentiful. Waiting until KONDA to object puts you at the edge of the high terrain with little time and fuel to negotiate.
3. ATC replies: 'Negative, maintain 9,000 for opposite traffic at 11,000; report KONDA.' What do you do?
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'UNABLE DUE TERRAIN' is the first transmission, not the start of a negotiation. A clearance never overrides the minimum altitude, and the pilot in command is responsible for terrain clearance at all times.
Sequence:
- State the problem and the requirement: 'UNABLE 9,000 DUE TERRAIN, REQUEST 11,200 OR A HOLD.'
- Give the controller options that preserve separation - a hold over lower terrain, a climb once the opposite traffic has descended, or a return to Moresby.
- If you are closing on terrain with no safe level available, declare an emergency (PAN or MAYDAY as the urgency dictates), climb to the minimum safe altitude, and tell ATC what you are doing. The rules give the PIC authority to deviate from a clearance in an emergency, with a duty to notify and to report afterwards.
- After landing, file the occurrence report and document the readback error and the emergency declaration. ATC will be doing the same from their side.
The one thing you must not do is fly the clearance because a controller issued it.