Jul 182013
 
Details of the holes burned through the fuselage of the 787 at LHR last Friday.

Details of the holes burned through the fuselage of the 787 at LHR last Friday.

Friday last week was a bad day for the 787.  A Thomson Airways 787 flying from Manchester UK to Orlando had to return to Manchester after flying slightly to the west of Ireland before then turning around.

The airline has declined to reveal the problem that caused the aborted flight, and the plane was quickly flying again.  But in view of the issues surrounding the 787, it would be comforting to know what happened on that flight.

However, that was merely the opening act prior to the main event.  At about 3.34pm, a person in the control tower at Heathrow noticed smoke coming from the rear of a parked Ethiopian Airlines 787, which was parked at a remote stand.  It had arrived from Addis Ababa at about 5.40am and after unloading passengers, was moved to the remote stand prior to flying out again that evening.

By happy coincidence, the remote stand was right next to an airport fire station, and so it took only one minute from when the controller raised the alarm until firemen were ‘in attendance’ (this contrasts with seven long minutes for fire trucks to reach the Asiana 777 at SFO a week earlier).  They quickly foamed the plane’s exterior and also played water onto where the damage could be seen.

Firemen then went into the plane, which was filled with thick smoke.  They used a portable Halon extinguisher to attempt to kill the fire, but that failed, and so they forcibly removed a ceiling panel and sprayed the area with good old-fashioned water from fire hoses.  This succeeded in extinguishing the fire.

Astonishingly, Heathrow was completely closed to all flights for almost two hours as a result.  It is not yet known if the plane will be repaired or scrapped, but we’d guess the plane will be repaired, no matter what the cost, so as to avoid Boeing the embarrassment of having suffered a hull loss on its new plane.

The event was – and still is – puzzling, because it happened on a parked plane that apparently had all electrical systems switched off.  After a series of inaccurate rumors and guesses as to the possible cause, the UK’s version of the NTSB (the AAIB – Air Accidents Investigation Branch) is now focusing on the Emergency Locator Transmitter (ELT) that was at that location, and which has its own self-contained (battery) power source.

But – and here’s the but.  There is some ambiguity as to whether the ELT was the root cause of the fire.  It seems likely that it was involved in the fire, but whether it started the fire, all by itself, or whether something else initiated a situation that caused the ELT’s battery to misbehave (the ELT has a type of lithium battery in it) remains unclear.

This was astutely first picked up in an excellent article by Christine Negroni on Wednesday evening, and echoed in a different form by the official AAIB report on Thursday.

Christine speculates (based on comments from people who are familiar with the plane’s wiring) that there may be some fundamental problems with the wiring on the 787, which apparently has a new form of insulation on it – a fragile type of insulation, and possibly it was an external wiring problem, close to the ELT, causing overheating which in turn may then have triggered the ELT’s battery to burst into flames.

The AAIB currently is more focused on the ELT itself, rather than any external wiring issues.  In its Thursday report, it says

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 of 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.

It also points out that more than 6,000 of this particular model of ELT have been produced, and this is the only time that an ELT has been involved in a ‘significant thermal event’.  It concedes this is an extremely rare event.

So is it purely and exclusively the fault of the ELT, or is it some other aspect of the 787 that triggered the possibly ELT based fire?

We don’t yet know the answer to that.  Meanwhile, the AAIB is recommending the ELTs be ‘inerted’ in 787s, and the safety of them in other planes be ‘reviewed’.

While there are some remaining unknowns, let’s think about we do know.

We know there are no fire monitoring or fire extinguishing devices in the ceiling of the 787.  And we further know that after the plane had been doused with water and foam externally, firefighters in breathing gear battled their way through thick smoke and were unable to put out the fire with portable extinguishers, needing to use hoses and water to extinguish the fire.

We also know that the fire burned right through the hull of the plane.  The carbon fibre material has a self-ignition temperature of about 580°F (only slightly higher than paper), compared to about 2000°F for airplane aluminium.  This is not the melting temperature, this is the temperature at which it will actually start to burn, itself.

We also know that burning carbon fibre generates copious amounts of FST – fire, smoke and toxicity.  For that reason, epoxy materials, such as are used to bind the carbon fibre, were banned from airplane interiors since the 1980s, but now they are allowed to be used for airplane exteriors – an exterior only fractions of an inch away from the airplane interior where they are banned.

Let’s now think what would have happened if the plane had been in the air at the time, somewhere three hours away from the nearest airport.  A fire that could not be detected until it was possibly too late, a fire that could not be extinguished, a hole being burned through the fuselage, and a cabin filled with toxic fumes.

Do you think that would be survivable?

Remember that the oxygen masks that drop down only provide maybe 10 – 20 minutes of oxygen (enough time for the plane to descend to a lower altitude where the outside air is thick enough to breathe) – after that, you’d be breathing whatever smoke and fumes remained.  The good news part of burning a hole in the fuselage is that might conceivably vent the fumes out, but a hole in the plane may weaken the entire structure with who knows what other negative consequences.

Even if none of this was a problem, the plane now has to fly at low altitude, where it will be burning twice as much (more or less) fuel per mile as up in the thinner altitudes – will it have enough fuel to fly three hours to its nearest airport?

Apparently I’m the only person worried about this.  There has been no further grounding order for the 787, and its 180 minute ETOPS rating remains unchanged.  So I guess you too should relax and not worry at all if you find yourself scheduled to fly on one of these planes.

I’ll quote the final paragraph and a half of Christine’s piece as a close.  It sums things up very clearly.

“It [the new fragile wiring insulation] will come and bite Boeing on the ass,” this person added.  “We have a lot of problems with this airplane because of the wiring.”

Much of the reporting of the Ethiopian Dreamliner fire of last Friday suggests Boeing has dodged a bullet since the blaze seems unrelated to its previous battery problems. But if the folks talking to me about overheating equipment, delicate wiring and airplanes that need their hands held are even in the vicinity of correct, there’s more to worry about on the world’s most modern airplane. Time for the hand-wringing to begin.

  One Response to “Heathrow 787 Fire – A One Off Event, or Indicative of a New 787 Vulnerability?”

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