Why Uncontained Engine Failures Are So Ugly


If you’re a YouTube aviation video junkie, you’ve probably seen this one of what’s called a blade-out test. It’s intended to prove that the containment around a high-bypass turbofan engine can prevent shrapnel from ricocheting outside the engine in the event that the fan loses one or more blades. Or the engine core comes asunder. It’s an expensive test, since it involves trashing a multi-million dollar engine, and it’s considered to be a big deal because uncontained failures are potential nightmares. Thankfully, they’re rare.

But not unknown, as the BA 777 explosion and fire in Las Vegas proved this week. While it hasn’t been officially declared an uncontained engine failure, the Las Vegas incident surely appears to be just that. And if it is, it shows why the engine manufacturers invest so much in containment design, because if a shattered fan or disc gets loose, the chaos it can cause is staggering.

The NTSB lists a small number of minor uncontained failures, but the one most of us remember is UA 232, the DC-10 that had its entire hydraulic system taken out by an uncontained fan disc failure in 1989. Recall that Captain Al Haynes and his crew managed to land the airplane at Sioux City, Iowa, with loss of life, but also many survivors. It turned out to be a landmark accident in shaping cockpit resource management and a wakeup call for system placement and design.

But a more recent uncontained failure was, in some ways, just as harrowing. I knew about the fact pattern in general terms, but I’d never read the details (PDF). It involved an Airbus A380 in 2010 fitted with the very same Rolls-Royce Trent 900 engines under test in the video above. It was a turbine failure, all right, but for the most mundane of reasons that led to a chain of events no one could have imagined.

A small oil pipe was bored slightly off center during manufacturing, yielding too-thin walls that cracked under fatigue stress. An aerosol mist of leaked oil ignited, causing the intermediate turbine—that’s toward the rear of the engine core, not the fan—to separate from its shaft and accelerate unabated until it burst. You may recall seeing the photo of the wing pierced with a manhole-sized crater, but that wasn’t the worst of it. The shrapnel chewed up wiring—more than 600 were damaged—to the extent that the crew had to land with inoperative leading edge devices and spoilers, reduced braking and an inoperable thrust reverser on the failed engine, the inboard on the left side. (The A380 has reverse thrust only on the two inboard engines.) The aircraft landed 95 tons overweight, with the remaining engines degraded and with reverse on only one engine. It stopped within 500 feet of the end of a 13,123-foot runway.

The passengers evacuated safely, but not until about 50 minutes after touchdown, evidently because of spilled fuel and a number-one engine that wouldn’t shut down due to wiring damage. It also took the airport time to round up airstairs.Firefighters finally drowned the runaway engine in water and foam, but it took three hours. (Yes, big engines like that are tested to ingest enormous amounts of water, too. They do.) The A380 incident was the first uncontained failure of a third-generation, high-bypass turbofan. Despite Rolls-Royce having focused everything that was known about jet engines on its design and having tested it to destruction, it wasn’t enough.

Still, everyone survived because the crew performed admirably and there was enough redundancy to keep the airplane under control in the air and on the runway. Just. But no rational person would be comfortable stretching the margins to such molecular limits. Chasing the problem upstream, investigators traced it to faulty quality control processes at Rolls-Royce; an improperly positioned tool jig, one tiny operation in an airplane that requires millions of such steps.

We’ll follow developments on the BA fire at Las Vegas, but I won’t be surprised if chance played a role in that one, too. Had the failure occurred 10 seconds later or later in the flight, the crew could have had both an engine failure and a massive fire. A Boeing 777 training captain who corresponds with us told us the rejected takeoff module is the most challenging part of jet transport training. “It happens fast in real life and requires the pilots to work through the fog of shock, surprise and crisis. For sure, a very busy process,” he said. For the BA crew, add a greasy orange fire and a column of thick black smoke.

They earned their money on that one. Eventually, we’ll find out why they had to.