Night VFR into Marginal Weather with Fuel Pressure Fluctuation
You are flying a single-engine piston helicopter on a night VFR cross-country leg of 95 NM. Departure fuel was 220 litres; current fuel is 150 litres, giving an endurance of about 1 h 50 min at 110 litres/h. Planned destination weather is temporarily 2 500 m visibility with scattered cloud at 1 200 ft AGL, but the destination has no instrument approach and no radar service. En route, 25 NM from destination, the fuel pressure gauge begins fluctuating between 2.0 and 2.8 bar (normal 2.5–3.0 bar) and the engine-driven pump warning light flickers intermittently. The collective is at 60% torque, Nr stable, TOT normal. You have 20 min of legal night VFR fuel reserve remaining after landing. A suitable alternate with a lit runway and reported 10 km visibility is 18 NM off track, adding 12 min. ATC offers vectors but cannot confirm your fuel state.
1. Decide whether to continue to destination, divert to the alternate, or declare an emergency, and justify your decision using fuel, weather, and system-status reasoning.
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Decision: divert to the alternate now and advise ATC of the fuel-pressure anomaly.
- Fuel: 150 litres at 110 litres/h gives 1 h 22 min usable flight time, not 1 h 50 min; the stated endurance figure must be checked against actual burn. Diverting adds 12 min, leaving roughly 1 h 10 min, which still preserves the 20 min night reserve plus a 30 min planning buffer. Continuing to a destination with no approach and deteriorating visibility risks a go-around with no alternate fuel.
- Weather: 2 500 m visibility and scattered cloud at 1 200 ft is close to night VFR minima and may deteriorate further. A destination without an instrument approach offers no recovery option if the cloud base lowers.
- System: A fluctuating fuel pressure with an intermittent engine-driven pump light suggests a failing pump or vapour lock. It is not yet a confirmed failure, but it degrades the redundancy margin. The alternate has a lit runway and 10 km visibility, reducing the workload needed to manage a possible pump failure.
- Action: Turn toward the alternate, reduce power slightly to lower fuel flow, monitor pressure and TOT, and inform ATC. Do not declare an emergency yet, but state the anomaly and request priority if pressure falls below 2.0 bar or the light stays on.
2. Explain how you would manage the fuel-pressure anomaly during the diversion and what thresholds would trigger an emergency declaration.
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In-flight management:
- Confirm the indication: cross-check the gauge against fuel flow, TOT, and engine roughness. A true pump failure usually produces a pressure drop with rising TOT or roughness; a pure gauge fluctuation without those signs is less urgent.
- Reduce demand: lower collective to the minimum safe cruise torque, lean the mixture per the POH, and select the auxiliary pump ON if the checklist permits. This reduces vapour-lock risk and preserves fuel.
- Monitor: record pressure every 2 min and note whether the warning light is steady or intermittent. A steady light with pressure below 2.0 bar is a confirmed failure.
- Plan the approach: fly a stabilized approach to the lit runway, keep a high-ish approach path to allow a power recovery, and brief a forced-landing option.
Emergency thresholds: declare an emergency if pressure falls below 2.0 bar and stays there, if the light becomes steady, if engine roughness or TOT exceed limits, or if fuel remaining falls below 30 min. At that point request priority landing and emergency services.