On 15 December 1989, KLM Flight 867 en route to Narita International Airport....

On 15 December 1989, KLM Flight 867 en route to Narita International Airport, Tokyo from Amsterdam was descending into Anchorage International Airport when the Boeing 747-400 flew though a thick cloud of volcanic ash from Mount Redoubt.All four engines failed leaving only critical systems on backup electrical power. After descending more than 14,000 feet, Captain Karl van der Elst and crew were finally able to restart the engines and safely land the plane. In this case the ash caused more than $80 million U.S. dollars in damage to the aircraft, but no lives were lost.

When all four main generators shut off due to the failure of all the engines, a momentary power interruption occurs when the flight instruments transfer to standby power. Standby power on the 747-400 is provided by two batteries and inverters. The captain performed the engine restart procedure which was not successful on the first few attempts and was repeated until restart was achieved. On some of the attempts, as one or more (but not all) engines started to operate, the main generator would switch back on. This switching on and off caused repeated power transfer interruptions to the flight instruments. The temporary blanking of the instruments gave the appearance that standby power had failed. These power transfers were later verified from the flight data recorder.