The blaze began in a battery in the unit made by Honeywell International Inc. (HON), the U.K.’s Air Accidents Investigation Branch said in a report released today. The battery wires were improperly installed, and an inspection of the beacon’s flame-damaged case suggested a short circuit, the agency said.
“This incident has highlighted that better coordination is required between battery manufacturers, equipment manufacturers, aircraft manufacturers and regulators to ensure equipment-level and aircraft-level safety,” the agency said.
The report into the July 2013 fire on the Ethiopian Airlines Enterprise Dreamliner confirmed investigators’ preliminary focus on the battery wiring. The blaze initially stirred fresh concern that the 787 had a serious electrical flaw after the global fleet was grounded following two meltdowns on a separate lithium-ion battery system.
U.S. regulators that oversee Chicago-based Boeing should develop standards for certifying lithium-metal batteries in aviation, the U.K. board said. Batteries on the Honeywell-made beacons are of the lithium-metal type, and have a different chemistry than lithium-ion models.
The U.S. Federal Aviation Administration should ask manufacturers to determine the worst possible effects of a thermal runaway and to demonstrate that damage to a single battery cell wouldn’t spread to others, causing a fire, the U.K. board said. The FAA and Boeing didn’t immediately respond to requests for reaction to the report.
The FAA told operators last year to inspect planes with certain Honeywell-made beacons, which are used in thousands of aircraft.
Lithium-metal batteries are high-energy storage devices that aren’t rechargeable, unlike the 787’s rechargeable lithium-ion batteries. While Honeywell created cell separators and safety vents to mitigate the risk of thermal runaway, all five cells of the beacon’s battery overheated, the British safety board determined.
The “most probable cause” of the Heathrow 787 fire “was a short-circuit caused by the improperly installed battery wires, leading to an uncontrolled discharge of the battery,” the board said. “This condition in isolation should not have caused a battery thermal event, if the battery short-circuit protection features had effectively limited the current to a safe level.”
The locator transmitter is used to notify authorities of an aircraft’s location in the event of an emergency. It can be set off by an internal sensor or manually by flight crew.
According to the report, Honeywell became aware of battery wiring issues in the same beacon used in the Ethiopian jet in February 2013 when one was returned with wires trapped under the cover plate. There was no evidence of thermal damage and no inspections or modifications were made, the U.K. board said.
Mandatory inspections of all other Honeywell beacons of that model after the Heathrow fire turned up 26 cases through mid-March in which trapped wires were found, according to the U.K. report.
In May, Honeywell routed the wiring underneath the battery on all ELTs to prevent the wires from becoming trapped. The Morris Township, New Jersey-based company is looking at other options “to improve the robustness” of the short-circuit protection feature on the beacon batteries, the report said.
Honeywell has worked with regulators in the U.S. and Canada, where the batteries are made, to assure that all of the designated beacons are inspected “to verify that the error is not present,” Steve Brecken, a company spokesman, wrote in an e-mail.
To contact the editors responsible for this story: Ed Dufner at email@example.com Romaine Bostick