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The small off-the-shelf electronic device at the center of the investigation of a fire aboard a Boeing 787 Dreamliner at Heathrow airport last month contains a fail-safe mechanism that should have prevented overheating even in the event of a wiring short-circuit, a Honeywell spokesman confirmed Friday.

The Emergency Locator Transmitter (ELT), supplied to Boeing by Honeywell and used in many other aircraft besides the 787, contains a current limiter — a standard feature, like a fuse, that shuts off the current if it gets above a certain level.

Boeing and government investigators inspecting the damaged ELT from the Ethiopian Airlines jet found that internal wires connected to the device’s lithium battery had been trapped and pinched when the cover was reattached as the batteries were inserted.

That led to a theory that the pinching of the wires compromised the insulation, and that crossed wires short-circuited to start the fire.

Honeywell spokesman Steve Brecken said Friday that the ELT contained a current limiter that should have stopped any surge of current caused by a short.

Did the limiter somehow fail? Or was the fire started some other way?

Brecken said all that’s known is that the fire was “in the area” of the ELT and that the investigation led by the U.K’s Air Accidents Investigation Branch is continuing. “We don’t know that the current limiter failed,” he said.

The Wall Street Journal reported Friday that Transport Canada, the aviation regulator in Canada, is preparing to order the inspection of ELTs in all types of planes carrying the device, including Airbus and Dassault.

Last week, Boeing sent out a service bulletin to operators of all its planes — not only the Dreamliner — recommending inspections of the ELTs.

The ELT is manufactured and assembled by a Honeywell subcontractor, Instrumar, of St. John’s, Newfoundland. Instrumar’s main business is technology connected with the production of carpet fiber, and the ELT appears to be its only aerospace product.

Brecken said Instrumar ships the ELTs for the 787 to Honeywell’s Deer Valley facility, near Phoenix, Ariz., and from there they are sent to Boeing.

He said Instrumar ships ELTs for other aircraft and for other manufacturers to Honeywell’s Mississauga facility, outside Toronto.

The Journal said Transport Canada this week inspected the Mississauga facility and will inspect Instrumar’s plant next week.

Dominic Gates: 206-464-2963 or