First a word about aircraft strength. Transport category aircraft are certified to a standard known as FAR Part 25 which dictates among other things ultimate load limits which the aircraft must survive. One of these limits is the 55 feet/sec gust (essentially a huge thunder storm), while traveling at Vmo. That's ALOT of stress on the wingspar, and the fuselage. The fact that an aircraft can be built light enough to get airborne, withstand high speed flight loads, but still maintain a shape resembling an aircraft after running across the ground and falling into a ravine without wheels at 145 kts is a testament to the relative strength of the airframe. Try that with any car short of a Hummer.

As for the cause of the accident, at this point we know absolutely nothing about what caused the departure from controlled flight. If you feel you MUST speculate, please at least consult a pilot, or have detailed operation of flight operations, or at the very least access to someone who does.

Though I usually avoid commenting before the experts do, as I hold a commercial multi-engine rating and have some turbine time, I can at least present some possible options:

* tire blow out: If anyone ever has had a blowout of a front tire in their car at highway speeds, you know exactly what kind of challenge you face with directional control if one of them goes. V1 (go / no go speed) in a fully loaded 737-500 would be around 145kts. Complete loss of left tire would cause a severe asymmetric rolling moment, and if the crew hesitated on the rudder (or maybe ran out of rudder given wind gust and gear drag), they simply may not have had enough time to catch it. From the track marks though, it looks like both gear were intact at runway departure

* Asymmetric (split) flap / incorrect flap condition - there is some speculation the aircraft went airborne for a moment or so. If the flaps had been mis-set, or worse, had an asymmetric setting (mechanical failure), this may have caused the aircraft to momentarily roll or even yaw left, and again, depending on the reaction time of the crew, the yaw moment may have been too quick to catch.

* Uncommanded left-rudder movement - Over there years, there have been numerous incidents involving uncommanded rudder movement in 737s, including a speculated one in Steamboat springs with United airlines several years back. Uncommanded flight control movements, needless to say are as dangerous as in-flight fires, as they can render the aircraft uncontrollable in a matter of seconds, and lead to catastrophic results, especially near the ground. An uncommanded left rudder movement could easily have given enough steering yaw moment to have the aircraft depart controlled flight, and off into the grass.

There are other failure modes possible, but I think you guys get the idea. Again, speculation about accident is understandable, but please try to make it based on rational possibilities, and not simply fantastical guessing.

Thanks

-avi

 Reply

And he took Continental's offer of a replacement ticket two days later. That guy was one tough (or mad) nut, for sure.

 Reply