News Accident: Southwest B737-700 N766SW near Pensacola, FL catastrophic engine failure

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Linguofreak

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Thunder Chicken said:
So how did debris get thrown into the side of the fuselage if the turbine disks are intact? The only thing that makes sense is the bleed air used for the cowl anti-icing overpressurized it and blew off the cowl, but that normally wouldn't be much more than 40 psi. It would take a fair amount of pressure to slam something against the fuselage fighting a several-hunded knot slipstream.
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I'll note that 40 psi is quite a bit greater than the total (static + dynamic) pressure (about 6 psi) at a 737's cruising speed (Mach .785) and the altitude of the accident (31000 feet).

It's also nearly three freakin' tons per square foot.

"Not much more" than 40 psi is well more than enough.

Are they sure that the cabin was actually breached, or did the bleed air system get compromised (which would lead to loss of cabin pressurization)?
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Well, there's a very visible gouge in the cabin in one of the photos upthread, so there's no question that something *did* hit the fuselage, and, given the size of the gouge and that pressure loss did occur, I'd say it's very likely that debris not only struck the cabin, but actually penetrated it. Damage to the bleed air system could also have contributed, but the gouge alone was likely sufficient.

As to *how* debris was thrown with sufficient force to strike the cabin at that spot, it was mentioned upthread that the cause of the cowling failure is thought to have been fatigue or bleed air overheat. If one of these factors opened up a hole on the leading edge of the cowling, there would have been considerable force of air entering the cowling through that hole, which I think could easily have caused the cowling to rupture explosively.

My dad also notes that the pressure in the inlet in normal operation would be quite considerable, so even if there wasn't exterior air blowing into the interior of the cowling itself, a structural failure of the cowling could lead to pieces of it being blown outward by the inlet pressure.

I'll also note that the pics show a spar bent back at least 90 degrees from the position I estimate it originally lay in. Imagine that that spar had a piece of cowling shell stuck to it, and that piece was being dragged back in the airstream, bending the spar back. Imagine that piece of cowling coming apart as the whole assembly snapped back. Given that the spar seems to have remained rigid along its length, and only seems to have bent at the base, anything that broke off when the spar was bent back between, say, 30 and 60 degrees would have had considerable velocity inwards toward the fuselage.

And if the bleed air did pressurize the cowling to 40 psi before it failed, that would send things flying *even faster*.
 
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