Night Departure with a Suspect Alternator
You are the sole pilot of a single-engine, normally aspirated airplane departing a mountain-adjacent field at 22:40 local. Field elevation 4,200 ft, temperature 18°C, density altitude computed at 6,900 ft. Useful load allows full fuel plus one passenger. During the run-up the ammeter shows a slight discharge at 1,000 RPM that returns to near zero at 1,700 RPM. The battery was replaced six months ago. On the takeoff roll the ammeter again indicates discharge, and after gear/flap retraction at 500 ft AGL you notice the landing light dimming slightly and the ammeter needle sitting in the discharge arc. The alternator warning light is not illuminated. Terrain rises to 8,500 ft within 6 NM ahead, and departure routing requires a climbing right turn to a 9,500 ft MEAs within 10 minutes.
1. What is the immediate priority order, and how do the density altitude and terrain drive it?
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Priority is fly the airplane, maintain terrain clearance, then manage the electrical problem. Density altitude ~6,900 ft already degrades climb rate substantially; the airplane is heavy and the terrain ahead rises to 8,500 ft within 6 NM. A degraded electrical system is not an immediate control problem, but losing it can cost you flaps, transponder, lights, and - critically at night - pitot heat and radio/navigation. So:
- Establish a positive climb and turn toward lower terrain or the published departure path.
- Reduce electrical load immediately (landing light off, unnecessary avionics off, cabin heat blower off) to see whether the discharge reverses.
- Only then troubleshoot. Do not troubleshoot at 500 ft AGL over rising terrain at night. The density altitude means you should not count on a rapid climb to the 9,500 ft MEA; plan a route that keeps terrain margin while you decide whether to continue or return.
2. The ammeter stays in discharge and the warning light never illuminates. What does that combination suggest, and what is your decision point?
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A steady discharge with no warning light suggests the alternator is not producing output but the warning circuit (often triggered by a voltage differential or field condition) is not annunciating - a failed indicator, a tripped field/overvoltage relay, or a wiring fault. Treat it as a real charging failure regardless of the light. Decision point: with battery-only power at night over rising terrain, you have a finite and unknown endurance. Set a hard limit - e.g., if the discharge has not reversed within 2–3 minutes of load shedding, or if voltage drops below the level at which pitot heat and radios are reliable, turn back to the departure field while you still have terrain clearance and battery reserve. Do not press toward a 9,500 ft MEA at night on battery power. A precautionary return to a known field with runway lighting beats an unplanned electrical failure over high terrain.
3. What should you tell ATC, and how does that change your options?
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Declare the situation plainly: "[Callsign], single-engine, electrical failure, alternator not charging, request immediate return to [field], request vectors and terrain advisories." If you still have radio, ask for:
- Vectors clear of terrain and a descent profile you can fly without automation.
- Traffic advisories so you can rely on see-and-avoid if the transponder fails.
- Confirmation of runway lighting and, if available, an approach you can fly with minimal electrical dependency. Telling ATC early converts an unknown into a known for them and gets you priority handling; it also gives you a second set of eyes on terrain. If radio fails, squawk 7600 if the transponder still works, fly the last assigned/expected route, and land at the nearest suitable field.