British air-accident investigators, six days after a fire erupted inside a parked Boeing Co. 787 Dreamliner, urged that all emergency locator transmitters on 787s be temporarily disconnected, and called on U.S. regulators to conduct a broad safety review of such devices installed on other aircraft.
Emergency crews surround a Boeing 787 Dreamliner, operated by Ethiopian Airlines, which caught fire at London's Heathrow Airport in this July 12, 2013, still image taken from video.
Thursday's recommendations by the U.K. Air Accidents Investigations Branch provide the most detailed explanation yet of what investigators believe could have sparked the fire aboard the empty Ethiopian Airlines jet that was sitting on the tarmac at London's Heathrow Airport.
It sets the stage for likely regulatory action affecting the global 787 fleet, and for further investigative work to review the safety of certain types of lithium-powered batteries used to power such emergency transmitters on an array of jetliners, business jets and general aviation aircraft produced by Boeing, Airbus and numerous other plane manufacturers.
Investigators said detailed examination of the top portion of the Ethiopian jet near its tail—which showed "extensive heat damage" to insulation and the fuselage itself—indicates the fire was most intense at the site of the emergency locator transmitter, or ELT.
Damage to the plane's composite structure coincides with the location of the ELT and "its associated wiring," according to the report, and investigators determined "there are no other aircraft systems in this vicinity" that "contained stored energy capable of initiating" the fire.
Boeing's stock rose after the AAIB issued its statement, largely erasing losses it suffered after the fire occurred Friday.
The U.K. agency's interim report and nonbinding recommendations, which are expected to be embraced by the Federal Aviation Administration, stop short of pinpointing the precise cause of the fire. Rather, the report says it isn't clear whether some internal battery problem or external short-circuit sparked the fire. But the update does highlight that the probe is focused primarily on the behavior of the ELT.
Boeing said it supported the recommendations. The FAA and Honeywell International Inc. which makes the ELT, didn't have any immediate comment. Experts from Boeing, Honeywell, the FAA and the European Aviation Safety Agency are all participating in the investigation.
Even as the AAIB was putting out its safety bulletin, a spokeswoman for the agency stressed that the exact sequence of events, and the potential involvement of other parts on the plane, hasn't been fully determined.
"This is a preliminary report only," the spokeswoman said. "We are still investigating and looking at everything; these things can typically take months not weeks to establish the cause."
Honeywell has previously indicated it would support calls for temporarily removing or disconnecting the ELTs.
According to Thursday's safety bulletin, about 6,000 of the Honeywell-produced parts are installed on various aircraft world-wide, and the fire aboard the Ethiopian jet "has been the only significant thermal event."
In the event of a crash, the devices are intended to automatically transmit an emergency signal to help search crews locate the aircraft. Under U.S. rules, airliners are allowed to continue carrying passengers for up to 90 days with the ELTs inoperative or disconnected. Rules in Europe and other parts of the world are similar.
The FAA typically follows such top-priority recommendations issued by European accident investigators or regulators.
The report says the Ethiopian Dreamliner arrived early in the morning at Heathrow from Addis Ababa "after an uneventful flight" and the crew didn't report any technical problems. The aircraft's systems were shut down and it wasn't receiving any electrical power from the ground, according to investigators, though one of the airport's power cable was left attached to the aircraft.
Roughly 10 hours later, an employee in the airport's air-traffic control tower noticed smoke coming from the plane. When firefighters arrived and entered the jet, they encountered thick smoke and discovered a fire in the rear of the cabin, between the ceiling panels and the composite fuselage, according to the report.
In an unusual aside, the report notes that the incident "did not fall within the definitions of an accident or serious incident" under the auspices of the International Civil Aviation Organization, which controls how and when international aviation investigations are launched. But invoking British law, AAIB investigators decided to launch a formal probe under ICAO rules and asked the FAA and other parties to participate.
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