The explanation only needs 2 words.
Air Canada.
Aside from that:
The TSB reported that 3 of 5 cockpit panels went dark when the aircraft was enroute at FL360 about 4 minutes after levelling off at FL360, and the crew received EICAS messages "ELEC EMERGENCY", "IDG 1 OFF BUS" and "IDG 2 OFF BUS" amongst other messages followed by additional messages a few minutes later. The RAM Air Turbine deployed and restored electrical power about 7 seconds after the fault. The crew informed ATC of an electrical problem however did not declare emergency, the crew decided first to try to restore electrical power. While working the related checklist an APU start was listed by the checklist, however, the APU is limited to FL300 or below, hence the crew requested a descent. Descending through FL300 the crew started the APU and proceeded with the checklist to bring IDG #1 online and subsequently IDG #2. Full power was restored at the time the aircraft levelled off at FL240.
The electrical fault messages cleared from the EICAS except for the TRU2 transformer rectifier unit, TRU1 powered the systems that would have been connected through TRU2 however.
About 7 minutes after the electrical failure the autopilot was re-engaged. The crew advised they had restored some electrical power but still requested vectors and the longest runway available at Toronto as they were planning to land with reduced flaps. All ATC units involved assigned priority to the flight.
The TSB analysed with respect to declaring emergency:
In addition to the decision to continue to destination, the crew’s perception that an emergency existed only if the power could not be restored led them to delay declaring an emergency with ATC. Once main power had been restored, the crew believed that because they did not require priority for their approach into CYYZ, declaring an emergency was also not necessary.
However, due to the content of the flight crew’s transmissions to ATC, including informing them of complete electrical failure and loss of all navigation, all ATC units treated the flight as an emergency on their own accord, provided priority handling throughout the flight, and instructed emergency vehicles at CYYZ to be on standby.
If flight crews become aware of a situation that may jeopardize safety but do not declare an emergency with ATC, then there is an increased risk that should the situation worsen, the flight will still be airborne due to a lack of priority handling, or that it will land without emergency services standing by.
Interesting that the smoke detector systems are powered by the same system that was taken out by the fire. Makes perfect sense.
Last edited by underfire; 21st Sep 2017 at 22:48.