As the hunt for missing flight MH370 continues, UK air accident investigators have revealed how "unrobust procedures" meant all relevant black box cockpit voice recorder data were lost in an earlier serious incident involving a packed Malaysia Airlines jumbo jet at Heathrow.
The Boeing 747 had to return to the west London airport after significant vibration was noted on one of the engines shortly after departure for Kuala Lumpur, said the report by the Air Accidents Investigation Branch (AAIB).
During the approach to land back at Heathrow, all three autopilots disengaged, the cockpit displays and lights flickered and a series of fault messages were displayed.
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There was a subsequent loss of power to some systems but the captain, with 340 passengers and 22 crew aboard, managed to make a safe landing at 11.20pm on August 17 2012.
The jumbo jet had a cockpit voice recorder (CVR) - a device which can record the last two hours of cockpit conversations.
The AAIB, which classed the incident as "serious" in its report today, said the CVR continued to run for some time after the aircraft landed "and as a result all relevant CVR recordings were lost".
The AAIB said: "The investigation determined that the operator's procedures for the preservation of flight recording was not sufficiently robust to ensure that recordings would be preserved in a timely manner following an incident or accident."
The report said that Malaysia Airlines had "expressed willingness to address this issue" and updated its procedures.
The AAIB said there had been a series of failures within the aircraft's electrical system. The report listed action taken by Boeing after the incident.
The CVR and the flight data recorder comprise the black box equipment on passenger aircraft.
The boxes are actually orange and their recovery in the case of Malaysia Airlines flight 370 could solve the mystery of the plane's disappearance.