Here is some more information on the Honeywell Electronic Locator Transmitter and the installation/operation on the Boeing 787.
We asked Boeing about the prospect of interface between the ELT and the 787’s electrical system. Boeing told us:
In the event of an emergency, the ELT will be activated either automatically by means of an internal acceleration sensor—or manually by one of the flight crew via the flight deck ELT control panel.
At the time of the incident, there was no power to the airplane. The ELT was powering itself via its battery. When an airplane is in flight, the ELT still powers itself with no help from the airplane. It interfaces with the airplane via wires connected to the flight deck so that the pilot can activate the transmitter, if necessary. Turning on the transmitter doesn’t transfer any power to the unit. There is a co-ax cable from the unit that connects to the antenna (located on top of the fuselage).
As we noted in a prior post, Honeywell’s ELT in a different version was subject to an airworthiness directive from Canadian and European regulators. Reuters has this additional detail, including comment from Honeywell. The AD related to improper grounding, so an obvious question is whether there is a grounding issue with the 787 ELT that led to a short that prompted the fire. Investigations are still underway.
In any event, this appears to exonerate the 787. We still reserve final judgment pending a more complete investigation.
Boeing said that the ELT can be removed within one hour by the airline.
The New York Times has this update.