>>>Might need some help from OPNL_Guy on this one....
>>>As I recall Southwest had a 737-200 flying OKC
that lost an engine into Lake Texoma. (If you have to lose one, in a great big lake is a pretty good idea).
>>>The story I got was that the engine had some sort of catastrophic turbine failure and things happened just like they were supposed to...rather than stay on the wing where fire or shrapnel could cause a problem, the shear bolts broke and the engine fell into the lake.
You're really taxing my cranium, TxAg....
I don't recall what city-pair was involved, but the problem wasn't a turbine failure nor did the engine go into the lake (Texoma nor Bachman). What happened was something that had happened to several other 737-200s over the years as noted above, i.e. an aft "conebolt" failure.
If you'll look at the picture of the NWA 727-200 earlier in the thread, you'll notice the engine strut and the curved frame attached to it. If you turn that strut/frame 90 degrees with the frame on the bottom, that's pretty much the underwing mounting scheme on the 737-100s and 737-200s.
There are three conebolts that attach the engine to that curved frame. The bolts are sort of T-shaped at the base. The two conebolts at the front of the mount are oriented like this: |- -| (presumably to handle rotational stresses) and the single aft conebolt at the reat of the mount is oriented like: T (presumably to handle the fore/aft thrust stresses). I say "presumably" as I'm not an engineer, and this is how I recall someone explaining it to me long ago. (737doctor, feel free to chime in anytime...)
The single aft conebolt ( T ) is backed up by a steel cable, and should the aft conebolt fail (as has happened) the cable is supposed to let the aft end of the engine drop 1-2 feet from the surface of the wing. Sometimes, that cable also failed, and you then got a situation where the aft end of the engine dropped further than 1-2 feet from the bottom of the wing, and the engine essentially pivoted around the front two conebolts and eventually right off the aircraft. This is what happened to Piedmont/ORD
, and Delta/DFW
, and probably some others around the globe.
What happened to that SWA flight so long ago was that the aft conebolt failed (and the aft end of the engine dropped 1-2 feet) but that the back-up cable HELD, preventing a complete separation. Captain Bernie Ballard made a nice soft landing on 31L, nobody was hurt, and after repairs, the aircraft was flying again within a couple of days.
The culprit behind this, the conebolts themselves, were the subject of a couple of airworthiness directives (ADs) and the inspection intervals were tightened up so that the metalurgical problem could be caught earlier (which has apparently worked, since you never see conebolt failures anymore), and I think they also made changes to the materials used, as well as the back-up cable.
I should also note that the problems with the 727 engine separations came from lav ice ingestion, and the #3 engine seizing at high RPM, and then just torqing itself right off the aircraft. In that context, the engine mounts were indeed designed to allow the engine to shuck itself off. In the case of the 737-200s, that same type of mounting would have probably allowed the same thing (assuming that a rotating engine had suddenly seized) but that the 737 separations resulted from a different (unintended) problem, i.e. the aft conebolt and cable.
Bottomline, no SWA 737 engine ever dropped into the lake anywhere... (although the image of a 737 skimming the lake and dropping the engine like a Grumman TBM Avenger dropping a torpedo is sort of entertaining...)
[Edited 2004-05-11 14:38:22]
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.