Night VFR Fuel and Alternate Decision at an Uncontrolled Field
You are pilot-in-command of a single-engine piston airplane departing an uncontrolled aerodrome at 18:40 local time. Sunset is 18:55. Your destination is a paved, uncontrolled field 210 NM away with no published instrument approach and no fuel service after 19:30. Forecast en route winds give a groundspeed of 118 kt. Planned fuel is 180 L total; the engine burns 34 L/h at your chosen power setting. You have 12 L unusable and a 5-minute taxi allowance already consumed. During the climb you notice the left fuel quantity gauge oscillating between 60 and 75 L while the right reads a steady 55 L, and the ammeter shows a slight discharge with the landing light on.
1. Compute your available flight time and determine whether the planned flight meets a 45-minute night reserve. State the decision.
Read the worked answer
Usable fuel = 180 − 12 = 168 L. Taxi already consumed is separate; assume it is not part of the 168 L usable figure. Endurance = 168 / 34 ≈ 4.94 h ≈ 4 h 56 min. Flight time = 210 / 118 ≈ 1.78 h ≈ 1 h 47 min. Remaining after destination = 4 h 56 − 1 h 47 = 3 h 09 min, far above 45 min. Even allowing climb fuel and a 15-min approach, the 45-min reserve is comfortably met. Decision: fuel is not the limiting factor; the flight is legal on fuel. The limiting factors are daylight, the destination's closing time, and the electrical anomaly.
2. The destination closes fuel service at 19:30 and you cannot land before 20:25. What operational and legal considerations drive your alternate planning?
Read the worked answer
Arrival is after the fuel window closes and after sunset, so you are effectively planning a night arrival at an uncontrolled field. Because you cannot obtain fuel there, you must either carry enough fuel to divert to an alternate with service, or plan a technical stop. Under VFR you must be able to reach a suitable aerodrome with reserve fuel intact; the alternate must have service available at your ETA. Practically: pick an alternate within roughly 30–40 min flying time that is open after 20:30, verify its runway lighting and PPR requirements, and confirm you have night currency and a serviceable landing light. If no suitable alternate exists, the correct decision is to delay departure to the next morning rather than press on.
3. Interpret the fuel gauge oscillation and ammeter discharge. What is the correct response?
Read the worked answer
An oscillating quantity gauge plus a discharge with an electrical load indicates a probable electrical fault (sender, wiring, or alternator/generator output), not necessarily a real fuel fluctuation. Treat indicated fuel as unreliable. Cross-check with dipstick/totalizer figures and time-based fuel logs. The discharge means the battery is carrying the load; shed non-essential electrical load (landing light off until needed, pitot heat only as required) and plan to land at the nearest suitable aerodrome before battery depletion affects radios and flaps. Do not continue into night VFR with an unresolved charging fault and an unreliable fuel indication.