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An emergency beacon made by Honeywell is under scrutiny in the U.K. probe of last week’s Boeing 787 fire at London’s Heathrow Airport, a person familiar with the investigation said.

The U.K.’s Air Accidents Investigation Branch (AAIB) is looking at the plane’s emergency locator transmitter and hasn’t ruled out other potential causes for the July 12 fire, the person said. The official, who was familiar with the initial work in the investigation and wasn’t authorized to speak about the case, asked not to be identified.

Honeywell’s emergency beacons have been certified for use since 2005 without a single reported issue, Steve Brecken, a spokesman for the company, wrote in an email. “At this time it is premature to speculate on the cause of the fire,” he said.

New Jersey-based Honeywell has sent technical experts to Heathrow to help with the inquiry.

No one was on board the Ethiopian Airlines plane at the time of the fire, and the carrier is still flying its three other 787s while awaiting the results of the investigation.

Emergency locator transmitters (ELTs) emit a radio beacon after a crash to help rescuers find the plane.

The 787’s ELT, a small orange-colored box, is in the crown of the rear fuselage, slightly to the left of a small antenna fin positioned directly in front of the airplane’s tail fin.

Close-up photos of the damaged Ethiopian airplane show this is where the fire burned through the top of the fuselage.

In the event of a crash or a hard landing, the small antenna transmits a global-positioning-system location to satellites, which notify ground stations of the possible crash and its whereabouts.

The ELT is equipped with a small, low-power lithium-manganese battery, a form of rechargeable lithium-ion technology, so it can continue to broadcast after a crash.

The battery is a different chemical formulation than the larger lithium batteries implicated in two overheating incidents in January that prompted the grounding of the 787 fleet for three months.

Through June, Boeing had delivered 66 Dreamliners to 11 airlines and a leasing company.

The Federal Aviation Administration restricted the fleet from flying Jan. 16 after the lithium-ion batteries overheated on two aircraft, with one catching fire in Boston with no passengers aboard.

The FAA lifted the grounding in late April after Boeing devised a fix to prevent and contain potential battery overheating.

Boeing shares rose 3.7 percent Monday, recovering most of Friday’s loss, after the AAIB said it saw no direct link between the latest fire and the earlier battery blazes.

Seattle Times aerospace reporter Dominic Gates contributed to this story.

Dominic Gates: 206-464-2963 or