Air Accident Investigations Branch raises concerns that aircraft equipment powered by the batteries could be vulnerable in report on 2013 blaze
Investigators are calling for a safety review of all lithium battery-powered equipment on planes after a fire on board a parked Boeing 787 Dreamliner at Heathrow, which crew would have struggled to contain in flight, was traced to a tracking device carrying such batteries.
The blaze, on board the empty Ethiopian Airlines jet in July 2013, burned through the fuselage and filled the cabin with acrid smoke while the plane was parked at a remote stand on the runway.
Britain’s Air Accident Investigations Branch (AAIB) said that while the fire was caused by the plane’s lithium battery-powered emergency locator transmitter (ELT), the homing beacon used to find missing aircraft, there were concerns other on-board equipment powered by similar batteries may be vulnerable.
Its investigation found the ELT’s battery wires were “crossed and trapped” under the battery compartment cover plate, which probably created a short circuit that caused an uncontrollable increase in temperature, leading to rupture and fire emitting toxic fumes.
The trapped wires broke the battery seal, allowing flames, gas and battery decomposition products to escape.
A circuit protector that should have tripped proved inadequate, which allowed the flames to take hold in the fuselage, according to a 182-page report published on Wednesday. A new “slow blow” fuse, which offered enhanced protection to the circuit protector, had not been fitted to any aircraft by June this year, the report noted.
It recommended the US-based Federal Aviation Administration, the European Aviation Safety Agency and Transport Canada conduct a full review to ensure such batteries had acceptable circuit protection and complied with precautions for venting toxic gas.
Had the aircraft been in flight, the location of the ELT, which was above ceiling panels at the rear of the passenger cabin, meant crew or passengers would not have immediately noticed the fire. “It is not known how long it may take for such a fire to be detected and the location of the ELT could prolong the time taken to locate the source,” the report said.
Since the Heathrow incident, Boeing has added a specific section on fighting lithium battery fires to its flight attendant manual. But cabin crew might not locate the source of a non-visible fire because the aircraft’s environmental control system would distribute the smoke and fumes, the AAIB said. And if they did, crew on the B787 would have to stand on a seat or armrest to access it.
Without specific training, locating the flames would be challenging and unrealistic, and if a fire happened in flight, odour and fumes could hinder crew, while opening the ceiling panel could fuel and invigorate the fire with oxygen.
The jet’s rescue and firefighting manual did not at the time include the location of the ELT lithium battery, which meant firefighters tackling the blaze at Heathrow initially had no idea it could be a source.
The report highlighted “design vulnerabilities” in the battery and called for an overhaul of the certification process, parts of which were outdated, and more thorough testing of heat dissipation in the batteries.
At the time of the Heathrow fire, there were an estimated 3,650 identical RESCU 406AFN ELT batteries in service, fitted to numerous aircraft types, plus 2,900 similar batteries in portable ELTs.
The RESCU 406AFN ELT was part of the Boeing 787 Navigation Radio System (NRS) designed by US-based Honeywell Aerospace, who subcontracted the manufacture of the ELT to Instrumar Limited, who again subcontracted the development and design of the battery to Ultralife Corporation, in Newark, the report said.
Honeywell was not aware of any previous thermal “runaway” events. But the company did know of a battery wiring anomaly on a previous ELT returned in February 2013 by a manufacturer where wires were trapped under the cover plate – though this did not lead to a fire, the report said. As a result the Instrumar battery assembly instructions were modified to better contain the wires on new ELTs in April 2013, though not on those already in service.
Following the Heathrow fire, all similar units were subjected to a mandatory one-off inspection ordered by the US FAA. By August 2014, 35 had been identified with trapped wires.
Wiring had since been moved to underneath the battery and away from the cover plate on all new units of this kind. However, said the report, “with a battery service life of 10 years, it will be many years until all in-service RESCU 406AF and AFN ELTs have the inverted battery installed”.
Boeing said it was “confident the 787 is safe and we stand behind its overall integrity”.
In a statement, it added the AAIB report was “extensive and thorough”.
“We are committed to a process of continual improvement of our airplanes and we will carefully review the AAIB’s recommendations.
“It is important that any potential changes to the airplane’s design be reviewed with great care, and with due consideration for any potential unintended consequences of any change. We will work closely with regulators, operators and industry partners to ensure that the safety of the world’s commercial jetliners continues at the highest levels.”
Following the Heathrow incident, all of its Honeywell RESCU 406 ELT units were checked and confirmed to be in compliance with FAA regulations, it said.
A spokesman for Honeywell said: “Since 2013 we have worked closely with government agencies to issue inspection notices for all applicable ELT units and updated the design, Honeywell is committed to the safety of all its products”.
Source: The Guardian