Date: 201508
Local time of day: 0601-1200
Location: ZZZ.TRACON, US
Flight conditions: VMC
Aircraft: Beechjet 400
Operator: Fractional
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
ATC / advisory: TRACON ZZZ
Reporter organization: Fractional
Reporter function: Pilot Not Flying; Captain
Human factors: Confusion
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: While reducing power for initial descent the Master Caution started flashing; we noted the Right generator had fallen off line. After following abnormal check list we reset the Right generator; after approximately 15 seconds the generator fell off line again. Approximately two minutes later the Left generator fell off line; after completing memory items; both generators remained off-line. Continuing with the Emergency Checklist; we selected Emergency Power but there was no power available (there were no annunciators; engine instrument indication or radio available). We reselected Main Battery power and the Right generator came back online jumping erratically between 50 and 220 amps. We elected to continue to the airport with the battery and generator on. After landing we turned off the generator and continued to the ramp on the battery. Once secured on the ramp we again tried the Emergency Power with the engines running and shut down; we found it to be working correctly.

Callback: Reporter stated Maintenance did some troubleshooting and found the Left Engine Starter-Generator had seized and basically self-destructed. The Generator Control Unit (GCU) was damaged from the jumping high amperage/overvoltage of the Left generator. The Right Engine Starter-Generator had dropped offline to protect itself from the electrical power spikes and circuits that had been getting hot from the Left Starter/Generator electrical output.Reporter stated Maintenance also noted that Standby Battery power had not been available to the Flight crew due to the overheated wires and a reverse current issue to the Standby Battery Charging System caused by the failing GCU. The Hawker (BE-400XP) uses a Standby Battery in the nose compartment instead of a Static Inverter unit. TheRight generator did come back online after they had re-selected Main Battery power; but the effects of the failing GCU contributed to the continued erratic amperage fluctuations. He does not know if there is only one GCU; or one for each engine. Later; after arrival; with engines running again; Emergency Power was available. Maintenance believed the electrical circuits and GCU had cooled off enough to allow for transfer to Emergency Power. He has not heard of similar experiences from other pilots he has talked with.

Second narrative: Right Generator fail off line. Captain followed the Abnormal Check list to reset the Generator. Right generator tripped offline again followed by the Left generator tripping offline. Captain followed Emergency procedures and selected EMER. Power but none was available. We then selected Main Battery power and the Right generator came back online. At this point we elected to continue to [the destination] with both [Main] Battery and [Right] generator online.


Synopsis: A Hawker BE-400XP Captain and First Officer report about the Right and Left Engine Starter/Generators dropping offline during descent. No annunciators; no engine instrument indication or radio available. Emergency (Standby) Battery power not available when selected. Maintenance found Left Generator had self-destructed and the Generator Control Unit had failed.