Comments about technological history, system fractures, and human resilience from James R. Chiles, the author of Inviting Disaster: Lessons from the Edge of Technology (HarperBusiness 2001; paperback 2002) and The God Machine: From Boomerangs to Black Hawks, the Story of the Helicopter (Random House, 2007, paperback 2008)

Sunday, November 7, 2010

Qantas Flight 32: A reminder that turbofan engines still explode

Offering a few elaborations on the catastrophic engine failure on board Qantas Flight 32 last week, over Batam Island, Indonesia. The aircraft landed at Singapore's Changi Airport without injury to crew or PAX, but it could have been disastrous.

The engine in question (one of four mounted on the aircraft) is the Trent 972 model built by Rolls-Royce. It's a model specific to Qantas A380. Here's a link to a Rolls-Royce brochure on the Trent 900 family, with a helpful cutaway diagram.

This was the first such failure in the Trent 900 family. (An engine in the Trent 1000 family broke up in August while being tested, but I don't count that event, because testing is supposed to be rigorous and probe for problems).

The Australian Transportation Safety Board has focused on a breakup of a geared disk. The ATSB asking Batam Islanders to contact authorities if they come across a disk fragment as shown in this article at

The most alarming run of uncontained engine failures occurred in the late 1990s, mostly among one variant of General Electric's widely-used CF6 engine, which was exploding at an average of four times a year. Failures in later models of CF6 models remain a concern. But to be fair, the CF6 is an extremely popular engine so there are a lot of them.

A common pattern is for an uncontained breakup to happen at full power, during the takeoff run. Full power is when the disks experience the highest stress, rotating thousands of times per minute.

But there have been dozens of engine breakups in flight, as on QF32. The most famous was United Flight 232, which led to a crash-landing at Sioux City, Iowa, in 1989. The tail engine on this DC-10 exploded at altitude and its fragments cut all hydraulic lines to the control surfaces.The crew gained enough marginal control over the aircraft, using asymmetric engine thrust, to bring it down and save most of the people on board.

This reminded disaster historians of how Capt. Bryce McCormick innovated that technique 17 years earlier to bring his American Airlines DC-10 down safely to Detroit's airport, using just the engine thrust, after a cargo-door blowout over Windsor, Ontario, destroyed his ability to use the control surfaces. McCormick's plane didn't crash, it didn't end with any fatalities, and it took to the air again after repairs. See Chapter 5 of Inviting Disaster for how McCormick pulled it off.

McCormick's feat still stands as a landmark in crew emergency preparation and is one of only two airliner cases I know in which such a catastrophic loss of flight controls ended in a controlled landing with no fatalities. (The other was a DHL cargo flight in 2003 that landed safely at Baghdad after being hit by a missile that caused horrendous damage to the A300's wing and chopped the hydraulic lines). McCormick had the keen foresight, two months before the near-crash in June 1972, to train himself in a simulator on how to fly the DC-10 using only the engines. It had been his initiative alone; there was no formal curriculum on such a thing.

So that's one risk to safety, an uncontained failure severing essential controls. Another theoretical risk, which is extremely small given protective measures in modern aircraft, is that shrapnel will injure passengers in seats that happen to be in line with the shrapnel zone.

I believe the more significant risk is that an engine explosion early in the takeoff run will puncture a fuel tank and cause a fire around that wing, after the crew aborts and comes to a hard stop. This happened on a Boeing 737 after an aborted takeoff at Manchester, England. The cause of the fuel leak from a wing tank was catastrophic failure of the combustion-can casing.

But most uncontained engine failures don't cause any injuries at all and they're so exceedingly rare I wouldn't let it affect my travel plans. Major-carrier scheduled flights are much safer than driving, mile for mile. And how else is one to vault the ocean?
But this advice to passengers:
  • If there is any sign of a sustained fire when the aircraft is on the ground report it to a flight attendant. The flight crew's view to the rear is very poor, and engine instruments sometimes lie or are misunderstood. There was the case with a British Midlands 737 in flight where the left-hand engine started tearing itself to pieces; while passengers on the left saw it happen the information didn't get to the front of the plane. The flight crew in a series of misunderstandings and missed signals concluded the problem was the engine on the right side. So they shut down the single remaining good engine instead of the faulty one on the left. When the left engine finally went to pieces on the descent there was no time for a restart and the plane crashed short of the runway at Kegworth, England. Point being: accurate, timely communication of critical information from clear-headed witnesses to decision makers can be a real life saver!
  • Make sure you are familiar with the exit doors nearest to you and how to open them, say, in case the exit-row passengers haven't been paying attention. For example, sometimes removable over-wing doors become a problem if passengers behind you are pressing forward and denying you the space you need to get the door out of the way.
  • Put your shoes on but leave the hand luggage behind, including laptops, briefcases, and wheelie bags. If the cabin starts filling with smoke (it will rise to the ceiling and be very visible), you are in an extremely marginal situation so saving the luggage should not be on your list of concerns. Passengers and crew will have to work closely and cooperatively to get everyone out.

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