The aviation world quickly lost interest in a tail fire in a parked Ethiopian Airlines 787 at London Heathrow in 2013 when it was found to have been caused by a pinched wire in an emergency locator transmitter and not its then controversial underfloor lithium ion batteries .
However this last week’s release of the UK incident investigation by the AAIB has changed that.
It found that the fire that spread from the crash locator device into the crown of the aft cabin was fueled by the epoxy resin that glues together those layers of composite tape that comprise much of the fuselage of the Dreamliner, and would have been very difficult to locate and extinguish had the fire broken out in flight.
The AAIB report said that “the resin in the composite material provided fuel for the fire, allowing a slow-burning fire to become established in the fuselage crown, which continued to propagate”.
This was a fire that proved very difficult to control even with heavy duty emergency ground equipment at London’s largest airport. America’s safety regulator the FAA, which also certified the Dreamliner as safe, is now reevaluating the current flammability and toxicity testing of composite aircraft materials and studying new certification procedures for future use of resin bonded composites in airliners.
While the implications of the AAIB report might not make for comfortable reading if aboard a 787 flying a long and remote route it is important to keep a perspective on this otherwise troubling document. Airlines that use 787s would have no reason not be be aware of the need to ensure the safe installation of the emergency locator transmitter that suffered the unlikely fault that set fire to the fortunately parked not flying Ethiopian jet.
The report tells us that once a fire breaks out in a Dreamliner it can be fed by the glue within the layers of the composite structure, and we can surmise, destroy the integrity of the hull and cause a disaster in a fairly short period of time.
But the dangers of deep seated structural fires on metal alloy airliners are no less daunting, and are the reason why the drill in such emergencies is a rapid descent and an emergency landing or crash landing. It’s been that way since the early days of enclosed cabins in propeller aircraft, and perhaps much longer.
The literature on airborne fires suggests that they can destroy airliners within 18 minutes, if not sooner. The biggest risk that figures in airliner concerns these days is from shipments of lithium ion batteries in cargo holds (now all but banned world wide), or checked in passenger luggage contrary to specific and clearly communicated airline warnings to customers to keep such devices with them in the cabin.
Cabin crew have well rehearsed procedures to deal with the small number of spontaneous combustions of lithium-ion batteries now occurring on scheduled flights, and also in recent times, in airport waiting lounges.
The Ethiopian incident is a very very lucky break for air travel. It happened on the ground, and revealed risks in such composite structures not envisaged when they were designed into airliners. What doesn’t kill us makes us safer.