A Delta Airlines flight on Monday made an emergency landing after an engine failure. Passenger video of the failed engine (see link) in the MD-88 showed the turbine spindle’s nose cone, separated from the spindle and being bounced around on the engine inlet grating by the slipstream while the fan blades windmill away behind the grating. Most notable in that video is that the forward end of the spindle, normally hidden by that nose cone, appears to be glowing red-hot. WTF is that? Is that just a spindle bearing that’s failed and is absorbing unholy amounts of mechanical power as the turbine is forced to spin by the slipstream?
I’ll go ahead and give a semi-educated guess until one of the more knowledgeable folks turn up. Behind the nose bullet is supposed to be the accessory dive cover. It’s hard to tell with all the spinning, but I think it’s come off as well. It looks like an exposed No. 1 bearing and N1 tachometer drive gear. The glowing metal is probably the front accessory drive attachment flange.
Bear Nenno if that’s a semi-educated guess I’d love to see a fully educated one!
How many serious answers do I have to wait for until I can quote from Patriot?
I saw a thread on Reddit that said “…the engine was shutoff at this point. The blades have been spun up by the forward velocity of the plane with the other engine. The bearings are orange hot because of lack of lubrication due to the engine being off yet still rotating.”
It’s on the internet, it must be true.
“Don’t you know? It’s all done with ball bearings these days.” — Gordon Liddy
It may be true, but it’s hard to believe.
Right. Aircraft engines are designed to be fine when turned off. A plane could lose all of its engines at 30,000 feet and glide to safety, all without the engines melting or catching fire, despite the forward movement of the aircraft still causing them to turn. If it’s the No 1 bearing itself that is glowing, then it’s probably from foreign metal debris getting in there.
There’s not enough information about this yet to draw conclusions, but that glowing #1 bearing might be the cause of the failure rather than an effect.
That is, a disintegrating #1 bearing would heat up as the turbine spins and perhaps stay hot after engine shutdown as the fan gets spun by ram air. Theoretically, such a large thermal gradient could distort the fan spinner hub enough to detach the spinner (as seen in the video).
Or maybe the cause/effect arrow points the opposite way and an improperly installed spinner shed debris that ended up being ground up in the #1 bearing, which heated up and disintegrated as a result of that foreign object debris (FOD).
That hot bearing could have caused the engine failure or it could be an effect of the engine failure. It’s obviously too early to say which.
Bear_Nenno has more expertise here than I do, just to be clear. But whether the glow comes from the #1 bearing, the accessory drive gear or elsewhere, the glow likely comes froom turning the airflow’s kinetic energy into a fair amount of heat (as Machine Elf postulates).
And I agree with others that the Reddit theory doesn’t hold water: a healthy #1 bearing in a shutdown, spinning engine wouldn’t overheat just from spinning while shut down.
And, while we’re on the subject:
I’d tell you all about the plane that shot itself down, but that would be too far afield.
None of those cases indicated that the engines were healthy and operable after their gliding period. However there is at least one case in which engines were shown to be operable after about 15 minutes of gliding, and that’s British Airways Flight 9:
The engines didn’t restart in the air (kind of hard without fuel) but the Gimli glider had temporary repairs completed and flew out to a maintenance base 2 days later: