The US Federal Aviation Administration should develop enhanced certification requirements for the use of lithium-metal batteries in aviation.
The call came from the UK Air Accidents Investigation Branch following a fire on an Ethiopian Airlines Boeing 787 Dreamliner parked at Heathrow last summer.
The most likely cause of the fire on the Dreamliner was a lithium-metal battery, although no final conclusions have been reached, the Financial Times reported.
Dreamliners, which entered service in 2011, were temporarily grounded by regulators in January last year after batteries burned on two 787s.
These lithium-ion batteries, used to power some of Dreamliner’s electrical systems, are different to the one that caught fire on a 787 parked at Heathrow last July.
This lithium-metal battery powered the aircraft’s emergency locator transmitter used to trace the aircraft in the event it goes missing.
The AAIB said examination of the transmitter found evidence that its internal battery pack had suffered what is known as a “thermal runaway” – an increase in temperature and pressure that can lead to fire and explosion.
It added that, following work with Boeing and equipment maker Honeywell, the most probable cause of the thermal runaway was a short circuit caused by the way in which the transmitter’s battery wires had been “improperly installed”.
Shortly after the incident, the FAA ordered inspections of Honeywell transmitters on other Dreamliners.
Honeywell subsequently called for inspections of transmitters powered by lithium-metal batteries on all aircraft types. A total of 3,650 batteries identical to the one that caught fire at Heathrow were in service at that time.
The AAIB said 28 transmitters were found to have “trapped wires” around their batteries – but none showed signs of suffering a thermal runaway.
Honeywell, having become aware in February last year of “wiring anomalies” on one transmitter’s battery, introduced changes to the equipment’s assembly instructions to guard against a recurrence of the problem.
The AAIB said it was time to update the FAA’s minimum performance standards for lithium-metal batteries used in aircraft because these requirements were drawn up in 2000 and were partly based on a 1995 document drawn up by one of the regulator’s advisory bodies.
“The guidance and requirements in [this document], written in 1995 based on available knowledge, are now outdated and do not adequately take account of the progress in lithium battery technology and operational feedback over the intervening two decades,” added the AAIB.