Night Departure from Salalah with a Fuel-Flow Anomaly
You are the PIC of a single-engine helicopter (MTOW 2250 kg, twin PT6-type turboshaft) departing Salalah (OOSA) at 21:40 local on a VFR night medical transfer to Thumrait, 85 NM to the NNW. The aircraft has 480 kg of fuel, giving an endurance of 3 h 10 min at the planned 140 kt cruise. Five minutes after lift-off, climbing through 4500 ft, you notice the fuel-flow indication has dropped from 340 pph to 285 pph while torque remains steady at 78% and Ng is stable. You are in IMC-free night airspace, 12 NM from the coast, over unlit terrain with no suitable forced-landing site within 8 NM. The destination has no instrument approach for your type and is forecast to be clear. Company SOP requires landing at the nearest suitable aerodrome if any abnormal indication cannot be positively identified within 10 minutes.
1. Analyse the fuel-flow discrepancy and decide what action to take, justifying your decision against the SOP and the operational risk.
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The indications are internally inconsistent: fuel flow down ~16% with torque and Ng unchanged is more likely an indication fault (flow transmitter or wiring) than a real fuel-flow reduction. A genuine 55 pph drop would normally be accompanied by a torque or Ng change. However, an undetected real leak or partial blockage is a fire/engine-failure risk.
Apply the SOP: you have 10 minutes to positively identify the fault. Steps: cross-check with the other flow indications if fitted, compare fuel totaliser against calculated burn, check fuel quantity trend, and monitor TOT and Ng. If the totaliser quantity is falling faster than the indicated flow implies, treat it as a real leak and land immediately. If quantity matches the lower flow and all other parameters are stable, the indication is probably spurious.
Because you are over unlit terrain with no landing site within 8 NM and the destination is 85 NM away, the conservative decision is to turn back to Salalah (12 NM) rather than press on. Night, single-engine, no forced-landing site: the risk of continuing outweighs the operational benefit. Land, have the aircraft inspected, and re-dispatch.
2. State the fuel planning consideration that would change if you elected to continue, and calculate your revised endurance margin.
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At the reduced indicated flow of 285 pph, the fuel burn would be roughly 480 kg / 285 pph ≈ 1.68 h, but you should not rely on an unverified indication. Using the planned 3 h 10 min endurance at 140 kt gives 443 NM range; the 85 NM leg is 19% of that, so range is not the limiting factor.
What matters is the reserve. Under normal VFR night operations you need a final reserve (typically 30 min for a helicopter) plus a destination alternate if required. At 140 kt, 30 min = 70 NM. With 85 NM to run and 443 NM of fuel, the reserve is more than satisfied - but only if the flow indication is trustworthy. If it is not, your usable endurance is unknown and the reserve cannot be assured.
Conclusion: the calculation shows the flight is feasible on paper, but the uncertainty in the indication means the reserve cannot be guaranteed. That reinforces the decision to divert to Salalah and resolve the discrepancy before continuing.