The Federal Aviation Administration (FAA) is re-evaluating the flammability testing that was conducted to certify Boeing’s 787 Dreamliner and is “investigating new test methods” for future certification of such composite plastic aircraft, according to an accident report released Wednesday about the intense July 2013 fire aboard a Dreamliner parked at Heathrow airport.
The report by Britain’s Air Accidents Investigation Branch (AAIB) says the fire, previously determined to have started from a short circuit in a small lithium battery powering an electronic emergency beacon, was fed by the epoxy resin in the composite plastic that forms the plane’s fuselage.
The fire severely damaged the empty Ethiopian Airlines 787 and continued to burn even after the battery energy was exhausted.
“The resin in the composite material provided fuel for the fire, allowing a slow-burning fire to become established in the fuselage crown, which continued to propagate,” said the report.
Because of those findings, the AAIB says, the FAA is re-evaluating “the current flammability and toxicity testing of composite aircraft materials” and will research new test methods for future certification. The results have not been published yet.
An FAA official familiar with the certification standards said the incident “taught people something they weren’t aware of.”
Regulators had not anticipated the circumstances of the Heathrow fire when flammability tests were done on the 787 during certification, he said.
The fire smoldered in the ceiling of the aircraft above fire-resistant insulation blankets and burned outward, damaging the crown of the fuselage over an area of about 11 square yards, the report said.
“The standards used in testing didn’t assume there would be insulation to trap the heat and energy,” said the official, speaking on condition of anonymity because he was not authorized to discuss the topic.
The accident clearly demonstrates that if an intense fire starts on an airplane, the resin in the composites will burn and create a self-sustaining fire, said the official.
He continued: “The key is, what are the threats that could start such a fire and are they being addressed?”
Steps toward eliminating the specific cause of the Heathrow fire have been taken in the two years since the accident.
The report confirms the long-established root cause: A pinched wire inside an emergency-locator beacon in the rear cabin ceiling resulted in a short circuit that caused a lithium-battery cell to discharge and overheat.
The batteries in such devices were inspected, and battery supplier Honeywell redesigned the wiring and developed a protective fuse.
Small batteries in other devices throughout the 787 and other jets were given similar scrutiny to ensure their designs protected against initiating a short-circuit fire.
In a statement, Boeing said, “We are confident the 787 is safe and we stand behind its overall integrity.”
The report points out that the 787 passed FAA flammability tests during certification, including tests mandated under a so-called “Special Condition” addressing the possibility of in-flight fire.
However, the FAA re-evaluation of flammability and toxicity standards in light of the Heathrow fire could mean further government scrutiny of 787 safety.
The FAA official said federal regulators “will have to go back and look at the effects of any new standards on existing aircraft.”
Apparently anticipating that possibility, Boeing’s statement said, “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.”
The FAA itself did not respond to questions about the AAIB report in time for publication.
Tough to find
The AAIB report concludes that, if the fire had happened while the plane was in the air, the flight crew would have struggled to locate and extinguish the blaze in the 787’s ceiling.
Even Heathrow’s specialist-fire services found it difficult to locate the origin of the blaze in the top of the 787’s interior fuselage, the AAIB said.
However, thermal-computer models predicted that in flight, the cooling airflow over the jet’s exterior and the low outside temperature would have “substantially” slowed the propagation of the fire.
Boeing modeling concluded that the jet’s fuselage would have maintained its structural integrity.
But an in-flight fire would still have been very serious. The jet-maker’s engineers also concluded that such a fire could have depressurized the aircraft.
Heathrow’s firefighters also found the airplane cabin filled with “dense smoke.” But in the aftermath of the fire, the AAIB said, it was not possible to determine accurately the potential toxicity of the fumes produced by the fire.
The AAIB noted that “Boeing is reviewing their current test methodology to determine whether additional tests can be introduced to more accurately assess combustion products” from the burning of the 787 structure.
The battery that overheated and caused the fire was a nonrechargeable lithium metal battery, with different chemistry than the lithium-ion type used in the 787’s two main batteries.
The failure of the main lithium-ion batteries earlier in 2013 had grounded the Dreamliner fleet worldwide for more than three months before the Ethiopian incident.
The AAIB report makes clear the Ethiopian jet fire was unrelated to the previous main battery incidents.
Article originally published in the Seattle Times, by ,