Boeing is developing models to assess how environmental control systems might carry particles and gas from a fire in the emergency locator transmitter, in the wake of the Ethiopian Airlines 787 fire at London Heathrow.
The aircraft was parked and empty at the time but the unusual nature of the fire, which originated in the transmitter situated in the aft fuselage crown, has spurred a re-examination of test data.
Investigators found that ducts for the 787’s environmental control system had been damaged during the event.
Boeing has started building an airflow model to examine the dispersion of combustion products from a similar fire. Tests on transmitter battery failure showed that emissions include carbon monoxide, carbon dioxide and hydrogen cyanide.
While Boeing has verified that current toxicity data regarding the 787’s composite fuselage and cabin interior complies with requirements, the airframer is “reviewing” its test methods to see whether they can assess combustion products more accurately, says the UK Air Accidents Investigation Branch.
It states that the variability of combustion compounds and the effect of the aircraft’s environmental control system on smoke distribution make the quantifying of the nature and toxicity of smoke in a composite fire “difficult”. The system’s influence could complicate efforts to locate the source of a fire that is not immediately visible.
Boeing’s airflow analysis will cover operation of the environmental control system in its normal mode, as well as during cabin-smoke procedures. Results of the environmental control system airflow modelling “may influence” future design and certification standards, the inquiry says.
Certification requirements could also be adapted as a result of re-evaluation by the US FAA of flammability and toxicity testing methods for aircraft materials, partly to ensure that these methods are still suitable for checking propagation of flames on composite fuselage structures.
Source: Cirium Dashboard