Alternator failure on a cross-country to Be'er Sheva
While cruising at 2,500 ft VFR from Herzliya (LLHZ) to Be'er Sheva (LLBS) in a PA-28, you notice the ammeter showing a steady discharge and the alternator warning light is on. The battery is 12 V, 35 Ah, about three years old. You have dual GPS/comms, electric flaps, an electric fuel pump, a landing light and pitot heat. The engine is running normally and fuel quantity is 90 L. The nearest suitable aerodrome is LLHZ, 12 NM behind you; LLBS is 38 NM ahead. It is day VFR with 20 km visibility. ATC has not reported any problem. You have 1,500 ft available to descend.
1. What immediate actions would you take to confirm and manage the failure?
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First verify the indication: check the alternator circuit breaker, cycle the master switch if the checklist permits, and check the ammeter again. If the warning remains and the ammeter stays in discharge, treat the alternator as failed. Reduce electrical load immediately: turn off the landing light, pitot heat if not needed in day VFR, the electric fuel pump if the checklist allows, and unnecessary avionics. Keep one com and one navigation source. Do not reset a breaker more than the checklist allows. Advise ATC of the electrical failure and your intentions. The aim is to preserve battery power for radio calls, one navigation display and, if needed, one flap selection.
2. Estimate the electrical endurance and decide whether to continue to LLBS or turn back to LLHZ.
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A 35 Ah battery is not 35 Ah of usable capacity after ageing and with a high load; treat usable capacity as perhaps 50–60%. With one com, one GPS and basic instruments, load may be 8–12 A, giving roughly 1.5–2 hours theoretically, but an old battery and low voltage may cut avionics earlier. LLBS is 38 NM ahead, perhaps 25 minutes; LLHZ is 12 NM behind, perhaps 10 minutes. The conservative choice is to turn back to LLHZ. Continuing adds exposure with a failing electrical system and no need to do so. If you continue, you must have a clear plan for a no-radio or no-flap landing and keep the battery for the approach. Turning back keeps more margin.
3. How would you plan the approach and landing with this failure?
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Plan for a normal approach but assume electric flaps may not be available. Select flaps only when the runway is assured, and be ready for an asymmetric or failed flap position; use the checklist for a flapless landing if necessary. Keep the landing light off unless required. Make a full radio call early, before battery power is depleted, and state the electrical failure. Fly a stable approach with extra speed margin for the flapless configuration. After landing, do not shut down immediately if ATC needs a phone call; but do not taxy with unnecessary electrical load. Have the alternator and battery checked before the next flight.