IFR Flight Planning - Fuel, Alternate and the 'Nearest Suitable' Question
You are planning a night IFR helicopter flight from Muscat to a remote coastal site 210 NM away. The destination has no instrument approach; the only let-down is a visual circuit, and the forecast for your arrival window is BKN010 with a 2,000 m visibility and a temporary 800 ft cloud base. The nearest airport with an instrument approach is 55 NM away, with a forecast of SCT015 and 8 km visibility. Your helicopter burns 320 kg/h at cruise; the flight is planned at 1 h 05 min. You must carry a final reserve of 30 minutes. Company policy requires a destination alternate whenever the destination forecast is below the alternate-planning minima. The aircraft has 1,100 kg of fuel available at start-up.
1. Compute the fuel plan and decide whether the flight can be dispatched as planned.
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Fuel computation.
- Trip fuel: 320 kg/h × 1.083 h ≈ 347 kg
- Final reserve: 320 × 0.5 = 160 kg
- Contingency (typically 5% of trip, company-dependent): ≈ 17 kg
- Alternate fuel: 55 NM at cruise - assume ~0.25 h → 80 kg
- Total required: 347 + 160 + 17 + 80 ≈ 604 kg
Available fuel at start-up is 1,100 kg, so the fuel is not the limiting factor - there is ample margin.
The real question is the alternate. The destination has no instrument approach and the forecast (BKN010, 2,000 m, TEMPO 800 ft) is below the alternate-planning minima. Company policy requires a destination alternate. The 55 NM airport with an instrument approach and SCT015/8 km qualifies as a suitable alternate if it is forecast to be above its own alternate minima at your ETA, and if you have the fuel to reach it (you do).
Decision. The flight can be dispatched provided the 55 NM alternate is confirmed suitable (weather above its minima, runway/approach serviceable, night operations permitted) and the fuel plan includes the alternate. If the alternate is not suitable, the flight cannot be dispatched, regardless of the ample fuel.
2. What does 'nearest suitable' mean here, and why is the 55 NM airport not automatically the answer?
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'Nearest suitable' is not 'nearest'. It means the nearest aerodrome that, at the expected time of arrival, is expected to be usable: weather at or above its operating/alternate minima, a serviceable approach and runway, night operations available, and within the aircraft's fuel and performance capability.
Why the 55 NM airport is not automatically the answer:
- Weather must be checked at ETA, not now - SCT015/8 km is fine, but the TEMPO and the arrival time matter.
- Suitability includes approach type and night capability - does it have a night approach? Is the approach available at your ETA?
- Fuel and time - 55 NM is ~15–20 minutes; you must have the fuel to reach it after a missed approach at destination.
- The destination itself has no instrument approach, so a missed approach there means a visual go-around into BKN010 - the alternate must be genuinely reachable from that point.
Judgement. If the 55 NM airport is forecast below its own alternate minima, or its approach is not available at night, it is not suitable, and you must find another - or not go. The trap is treating 'there is an airport 55 NM away' as automatically satisfying the alternate requirement.