The United Kingdom's Air Accidents Investigation Branch (AAIB)has issued a special bulletin pertaining to a fire onboard a parked Ethiopian Airlines (ET) Boeing 787-8 (MSN 34744 | ET-AOP) at London Heathrow Airport last week has been released. According to the report, suspicions thus far point to the aircraft's Emergency Locator Transmitter (ELT) and its associated system wiring. On the basis of these initial findings and a recommendation from the AAIB, the US Federal Aviation Administration has said it is preparing to issue an Airworthiness Directive in the coming days that would make inspections of all ELTs aboard Boeing 787 aircraft, mandatory.
Herein lays an extract from the report pertaining to the preliminary AAIB investigation:
The AAIB's initial technical investigation confirmed extensive heat damage in the upper portion of the rear fuselage, with significant thermal effects on aircraft insulation and structure. Surveying and detailed examinations of damaged areas revealed that the greatest heat damage and highest temperatures were centred on the rear fuselage close to the crown and displaced to the left of the aircraft centre line. This corresponds to the most damaged external areas, with blackened and peeling paint and damage to the composite structure. It also coincides with the location of the aircraft’s Emergency Locator Transmitter (ELT) and its associated system wiring which is mounted internally on structure close to the aircraft skin. There are no other aircraft systems in this vicinity which, with the aircraft unpowered, contain stored energy capable of initiating a fire in the area of heat damage.
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| ET-AOP at Heathrow (AFP) |
The ELT model installed in the aircraft - the Honeywell International RESCU406AFN fixed Emergency Locator Transmitter - contains a set of chemical batteries using a Lithium-Manganese Dioxide (LiMnO₂) composition. These allow the ELT, as required by regulation, to operate in an emergency situation entirely independent of the aircraft’s electrical power system.
Detailed examination of the ELT has shown some indications of disruption to the battery cells. It is not clear however, whether the combustion in the area of the ELT was initiated by a release of energy within the batteries or by an external mechanism such as an electrical short. In the case of an electrical short, the same batteries could provide the energy for an ignition and suffer damage in the subsequent fire. The ELT manufacturer, Honeywell International, has produced some 6,000 units of this design which are fitted to a wide range of aircraft and, to date, the incident on 12 July 2013 has been the only significant thermal event.
The history of this ELT product line indicates that a thermal event is extremely rare and this incident occurred on the ground while the aircraft was unoccupied. However, large transport aircraft do not typically carry the means of fire detection or suppression in the space above the cabin ceilings and had this event occurred in flight it could pose a significant safety concern and raise challenges for the cabin crew in tackling the resulting fire.
The AAIB therefore makes the following two Safety Recommendations:
- It is recommended that the Federal Aviation Administration initiate action for making inert the Honeywell International RESCU406AFN fixed Emergency Locator Transmitter system in Boeing 787 aircraft until appropriate airworthiness actions can be completed.
- It is recommended that the US Federal Aviation Administration (FAA), in association with other regulatory authorities, conduct a safety review of installations of Lithium-powered Emergency Locator Transmitter systems in other aircraft types and, where appropriate, initiate airworthiness action.
The AAIB adds that a "detailed examination of the ELT and the possible mechanisms for the initiation and sustaining of the fire in this aircraft continues" with further updates on progress to be published as appropriate.
Download the full AAIB Special Bulletin here.
The FAA has issued its own statement in which it says that after reviewing the initial findings of the AAIB's report and recommendations, it is working with Boeing to develop instructions to operators for inspection of the Emergency Locator Transmitters (ELTs) on Boeing 787 aircraft. These inspections would ask operators to inspect for proper wire routing and any signs of wire damage or pinching, as well as inspect the battery compartment for unusual signs of heating or moisture.
The FAA is preparing to issue an Airworthiness Directive in the coming days that would make these inspections mandatory. Federal Aviation Regulations do not require large commercial aircraft in scheduled service to be equipped with these devices.
Download the full AAIB Special Bulletin here.
The FAA has issued its own statement in which it says that after reviewing the initial findings of the AAIB's report and recommendations, it is working with Boeing to develop instructions to operators for inspection of the Emergency Locator Transmitters (ELTs) on Boeing 787 aircraft. These inspections would ask operators to inspect for proper wire routing and any signs of wire damage or pinching, as well as inspect the battery compartment for unusual signs of heating or moisture.
The FAA is preparing to issue an Airworthiness Directive in the coming days that would make these inspections mandatory. Federal Aviation Regulations do not require large commercial aircraft in scheduled service to be equipped with these devices.