Air accident investigators have recommended the emergency locator transmitters on Boeing Dreamliners be deactivated pending further investigation following the fire on 787 at Heathrow last Friday.

The UK Air Accident Investigation Branch (AAIB) has also recommended safety checks on transmitters on other aircraft.

The recommendations came in an initial bulletin on the investigation which identified the emergency locator transmitter (ELT) on the aircraft as the source of the fire.

This reported damage to the chemical batteries in the transmitter, but said it was too early to identify the cause.

The transmitters are not peculiar to the Boeing 787. The same make has been installed on several thousand aircraft.

The AAIB stressed that the fire aboard the Ethiopian Airlines 787 was the first incident of its kind.

The Dreamliner was on a stand at Heathrow, where it had been parked for about eight hours, when smoke was seen coming from the aircraft.

Fire fighters doused the aircraft in water and foam before entering and encountering thick smoke from a fire above the ceiling panels at the rear

Investigators identified the area as the location of the ELT and associated wiring, reporting: “There are no other aircraft systems in this vicinity.”

The transmitter is designed to operate independently of the aircraft’s electrical power system, for use in an emergency.

It contains a set of lithium-manganese dioxide batteries. These are not the same as the lithium-ion batteries which led to the 787’s grounding for three months this year.

The AAIB said: “Detailed examination has shown some indications of disruption to the battery cells.

“It is not clear whether the combustion was initiated by a release of energy within the batteries or by an external mechanism such as a short circuit.

“The history of this ELT product line indicates a thermal event is extremely rare and this incident occurred on the ground while the aircraft was unoccupied.”

However, the AAIB said aircraft “do not typically carry the means of fire detection or suppression” in the area of the transmitter.

Therefore, the AAIB advised “making inert the ELT system in Boeing 787 aircraft until appropriate airworthiness actions can be completed”, and “a safety review of installations of lithium-powered ELT systems in other aircraft types”.

Boeing issued a statement saying it supported the recommendations “which we think are reasonable precautionary measures as the investigation proceeds”.

The manufacturer insisted: “We are confident the 787 is safe and we stand behind its overall integrity.”

The recommendations are not expected to affect Dreamliner operations. Thomson Airways confirmed its services to Cancun and Orlando would operate as scheduled.

A Thomson spokeswoman said: “All our 787 flights will operate as planned. We would never operate an aircraft unless we were 100% confident in its safety.”
She added: “This is not a Boeing 787 technical issue, but an ELT issue.”