Generator Failure and Battery Discharge at FL280
During climb through FL280 in a twin-engine business jet, the left generator trips. The right generator remains online, but the bus tie shows OPEN and the battery ammeter indicates 35 A discharge. The dispatch deviation guide permits flight with one generator for 90 minutes if the essential bus load is below 60 A. Current load is anti-ice 25 A, avionics 18 A, cabin 12 A, fuel pumps 8 A. The APU is available and its generator can be started up to FL350; however, APU start requires battery power, and the battery is at 68% and decreasing. Weather at destination is fine, but the alternate is 45 minutes further. The aircraft is in IMC and icing conditions are forecast above FL300. The QRH says do not reset a tripped generator more than once.
1. Analyse the electrical state: what is powering what, and what is the significance of the 35 A battery discharge?
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Left generator is offline and the bus tie is OPEN, so the right generator may not be feeding all buses. The battery is carrying 35 A. Total listed load is 25+18+12+8 = 63 A, so the 90-minute dispatch deviation is not met until load is below 60 A. Shedding cabin load (12 A) brings the essential bus to 51 A, which meets the guide, but the battery still discharges at 35 A unless the right generator/bus configuration is corrected. First verify right generator output, bus tie position, and that no other bus is isolated. A 35 A discharge on a 68% battery gives limited time; treat it as a serious electrical emergency, not a routine checklist item.
2. Would you start the APU, and how would you manage the battery?
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Start the APU promptly while battery is above the minimum for APU start, because the aircraft is in IMC/icing and the alternate is 45 minutes away. APU generator can restore bus power and stop battery discharge. If APU start fails or battery drops below the checklist minimum, shed all non-essential loads and divert to the nearest suitable airport. Do not delay the decision to try multiple resets. The battery percentage and discharge rate should be monitored against the QRH time curve; if the APU is available, using it is preferable to continuing on a discharging battery.
3. What checks would you complete before attempting a generator reset, and what are the risks?
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Before reset: confirm the generator is offline, no smoke or burning smell, no bus fault, and the QRH permits one reset. Do not reset if there is a known short circuit, if the generator tripped with a fault light, or if the bus tie is abnormal. A reset attempts to reconnect a generator that may have an internal fault; repeated resets can cause a fire or damage the bus. If it trips again, leave it offline and rely on APU/remaining generator. Record the event and advise maintenance.