A Qantas Airlines Boeing 747 jet climbing out of San Francisco on Monday experienced an uncontained failure of the number four engine. That means that the outside right-side engine failed so spectacularly that pieces of it penetrated the cowling, the case around the engine. The linked article has photos, and even though they were taken in the dark you can still see some of the turbine fan blades through the hole.
The pilots of course couldn't see the hole in the engine, only feel the vibrations through the airframe and see whatever indications the engine instruments reported. They certainly wouldn't have been normal. They shut the engine down, dumped fuel to get down to landing weight (you can see a couple of orbits on the Flight Aware track in the Flightglobal piece linked above), and returned for landing at San Francisco to investigate. Passengers saw flames and sparks coming from the engine; one of them took a video of the sparks streaking by, even after the engine was secured.
It's always interesting to see how pilots handle PAs in situations like this. (You can hear a little bit of the captain's announcement in the above video). Some companies give you a script, but the nature of emergencies is that they don't always suit the script. This captain emphasized that the crew train for this, and then I think he tried to throw in a bit of humour by saying, "in the simulator." He sounds calm, and I hope that calmed people down. Passengers tend to think they're all going to die whenever anything happens. The problem with reassuring people is that they always think you're lying to them, or at least that there's a reasonable chance of whatever you are saying won't happen, happening. My approach is to be honest, but a little bit vague about the problem and then distract them from worrying about imminent death by reassuring them that we will find them another airplane, and make sure they get to their destination. They can then worry about missed connections and lost baggage, which is not life threatening and returns them to the comfort of the habitual concerns of the air traveller.
This could have been worse if the containment failure had been on the left side of the cowling, (or the right side of an engine on the left of the airplane) because debris could have damaged the other engine or penetrated the cabin. Components leaving a turbine engine have a lot of energy. Those things rotate at over 10000 rpm.
LiveATC recording of the event from the perspective of the radio communications is available buried in this file. The Qantas pilots report their difficulties 18:20 into the recording. Eric M. has edited it down to the eighteen minutes directly concerned with the incident flight but you can only hear that version if you register (for free) at LiveATC.net. There's some confusion on the part of ATC, as Australia and the US seem to have different standards for the information an aircraft with an emergency must convey. Although the Qantas crew do deny they have an emergency. That means they don't believe they need any kind of priority to ensure safety.
An interesting detail about of the B747 is that it is equipped with a hardpoint for carrying a spare engine. Not connected up to fuel and power, just sitting there ready to be installed, like a spare tire on the back of your SUV. They don't carry one around all the time because they add a lot of drag and are very rarely needed. It's just a provision for transporting them. Another Qantas B747 will bring a spare in today for the one on the ground at SFO.
That's today's blog entry early, although I'll edit it to make it look like it appeared at 00Z as usual. Tomorrow's will be at the usual time.