by Devesh Agarwal
The United Kingdom’s Air Accidents Investigation Branch (AAIB) has issued a special bulletin (read PDF here) on the fire that broke out on Ethiopian Airline’s Boeing 787-8 Dreamliner ET-AOP, parked at London’s Heathrow airport last Friday.
In the report, the AAIB said the fire occurred in the rear upper fuselage where the fixed Emergency Locator Transmitter (ELT) is located. The ELT model RESCU406AFN is made by US aviation major, Honeywell International.
The report says
Detailed examination of the ELT has shown some indications of disruption to the battery cells. It is not clear however, whether the combustion in the area of the ELT was initiated by a release of energy within the batteries or by an external mechanism such as an electrical short. In the case of an electrical short, the same batteries could provide the energy for an ignition and suffer damage in the subsequent fire.
There are no other aircraft system in this area of the plane which, with the aircraft unpowered, contained stored energy capable of causing such a fire,
However, the report also gives some benefit of doubt to Honeywell, saying
The ELT manufacturer has produced some 6,000 units of this design which are fitted to a wide range of aircraft and, to date, the incident on 12 July 2013 has been the only significant thermal event
The AAIB has made two safety recommendations in its report:
Safety Recommendation 2013-016
It is recommended that the Federal Aviation Administration initiate action for making inert the Honeywell International RESCU406AFN fixed Emergency Locator Transmitter system in Boeing 787 aircraft until appropriate airworthiness actions can be completed.
Safety Recommendation 2013-017
It is recommended that the Federal Aviation Administration, in association with other regulatory authorities, conduct a safety review of installations of Lithium-powered Emergency Locator Transmitter systems in other aircraft types and, where appropriate, initiate airworthiness action.
Aircraft manufacturer Boeing released a statement saying
As a party to the investigation, Boeing supports the two recommendations from the UK Air Accidents Investigation Branch (AAIB), which we think are reasonable precautionary measures to take as the investigation proceeds. We are working proactively to support the regulatory authorities in taking appropriate action in response to these recommendations, in coordination with our customers, suppliers, and other commercial airplane manufacturers.
We are confident the 787 is safe and we stand behind its overall integrity.