What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
The sequence of events that lead to a complete electrical power loss on flight #542 can be summarized as follows:
It started off with the generator 1 gcu failure producing voltage fluctuations which triggered a battery caws caption. In response to that caution, the flight crew initiated a battery reset but the battery was actually never set to on again (as confirmed by the caws recording and other evidences such as propeller not feathering during engine shutdown and post flight inspection found the battery switch to off). With the absence of the battery, generator 1 voltage fluctuations got worse eventually leading to the total disconnection of gen 1. Under these conditions, generator 2 was the only source of electrical power. Moreover, the non essential bus was not automatically load shed (non essential override switch was found in the override position) and high current load like the vccs were still on, leading to the overload of the BAT/GEN2 tie. Once BAT/GEN2 tie opened, being also generator 1 and battery offline, the cockpit went completely dark.
Previous flight #352 underwent to a similar sequence (GEN1 offline, non essential bus not load-shed) with the only difference being that the battery was correctly switched back on after reset. Generator 2 and the battery could support all the electrical loads until landing and since the battery and the gen 2 lie on opposite sides of the BAT/GEN2 tie, the BAT/GEN2 tie did not trip.
As the FAA filed it
THE SEQUENCE OF EVENTS THAT LEAD TO A COMPLETE ELECTRICAL POWER LOSS ON FLIGHT #542 CAN BE SUMMARIZED AS FOLLOWS:
IT STARTED OFF WITH THE GENERATOR 1 GCU FAILURE PRODUCING VOLTAGE FLUCTUATIONS WHICH TRIGGERED A BATTERY CAWS CAPTION. IN RESPONSE TO THAT CAUTION, THE FLIGHT CREW INITIATED A BATTERY RESET BUT THE BATTERY WAS ACTUALLY NEVER SET TO ON AGAIN (AS CONFIRMED BY THE CAWS RECORDING AND OTHER EVIDENCES SUCH AS PROPELLER NOT FEATHERING DURING ENGINE SHUTDOWN AND POST FLIGHT INSPECTION FOUND THE BATTERY SWITCH TO OFF). WITH THE ABSENCE OF THE BATTERY, GENERATOR 1 VOLTAGE FLUCTUATIONS GOT WORSE EVENTUALLY LEADING TO THE TOTAL DISCONNECTION OF GEN 1. UNDER THESE CONDITIONS, GENERATOR 2 WAS THE ONLY SOURCE OF ELECTRICAL POWER. MOREOVER, THE NON ESSENTIAL BUS WAS NOT AUTOMATICALLY LOAD SHED (NON ESSENTIAL OVERRIDE SWITCH WAS FOUND IN THE OVERRIDE POSITION) AND HIGH CURRENT LOAD LIKE THE VCCS WERE STILL ON, LEADING TO THE OVERLOAD OF THE BAT/GEN2 TIE. ONCE BAT/GEN2 TIE OPENED, BEING ALSO GENERATOR 1 AND BATTERY OFFLINE, THE COCKPIT WENT COMPLETELY DARK.
PREVIOUS FLIGHT #352 UNDERWENT TO A SIMILAR SEQUENCE (GEN1 OFFLINE, NON ESSENTIAL BUS NOT LOAD-SHED) WITH THE ONLY DIFFERENCE BEING THAT THE BATTERY WAS CORRECTLY SWITCHED BACK ON AFTER RESET. GENERATOR 2 AND THE BATTERY COULD SUPPORT ALL THE ELECTRICAL LOADS UNTIL LANDING AND SINCE THE BATTERY AND THE GEN 2 LIE ON OPPOSITE SIDES OF THE BAT/GEN2 TIE, THE BAT/GEN2 TIE DID NOT TRIP.
Other reports on N220JP · 1
Matched to the same aircraft by N-number and date.