On Thursday morning, the UK Air Accidents Investigation Branch issued special bulletin concerning the investigation into a fire in a Ethiopian Boeing 787 at London Heathrow last week. The AAIB says that the focus of the investigation has zeroed in on the emergency locator transmitter, or ELT, located at the rear of the aircraft. Subsequently, the AAIB has issued two safety recommendations.
The ELT is a device which is activated upon an emergency that sends out a signal with crucial rescue information, such as aircraft identity and location, and can run on independent battery power for several days. “The ELT model installed in the aircraft contains a set of chemical batteries using a Lithium-Manganese Dioxide (LiMnO2) composition. These allow the ELT, as required by regulation, to operate in an emergency situation entirely independent of the aircraft’s electrical power system,” said the AAIB bulletin.
“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.”
Although noting that a thermal event caused by an ELT is “extremely rare,” however, the AAIB added “large transport aircraft do not typically carry the means of fire detection or suppression in the space above the cabin ceilings and had this event occurred in flight it could pose a significant safety concern and raise challenges for the cabin crew in tackling the resulting fire.” As a result, the following safety recommendations have been made:
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.
The bulletin also details the difficulty in fighting the fire. “They attempted to tackle the fire with a handheld ‘Halon’ extinguisher but this was not effective, so they forcibly moved a ceiling panel and tackled the fire with water from hoses. This was effective and the fire was extinguished.” Such actions while in flight would be extremely difficult to accomplish.
This specific type of ELT is manufactured by Honeywell, and over 6,000 units have been fitted to a “wide range” of aircraft. It is simply by chance that this ELT happened to occur on a Boeing 787. This fire, although caused by a type of lithium-ion battery, is completely unrelated to the battery issues the Boeing 787 suffered earlier this year. The AAIB noted that the Ethiopian 787 was attached to ground power cables, but all aircraft systems were completely powered down.
Immediately after the issuance of the AAIB bulletin, Boeing released the following statement:
The safety of passengers and crew members who fly aboard Boeing airplanes is our highest priority.
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.
Full text of the AAIB bulletin can be found here. [PDF Link]
