Originally Posted by
MACH6
Often, the SIMPLEST explanation is the correct one….
A NEAR VERTICAL dive in a B737 can only be caused by SUSTAINED PILOT INPUT.
After the SILKAIR MI 185 disaster in 1997, several scenarios including RUDDER HARDOVER, JET UPSET, ENGINE FAILURE, STALLS, DEPRESSURISATION and SUSTAINED PILOT INPUT were simulated by the human factors group, which were part of the accident investigation team. (see final report).
SUSTAINED PILOT INPUT produced a nearly identical rate of descent and just under 3nm lateral distance travelled.
The other scenarios didn’t get anywhere near the same descent or distance travelled.Also, the aircraft exceeded the local speed of sound, causing the ‘boom’ sounds locals heard in the final stages of descent.
I hope the recorders can be recovered in a usable condition. But like the SilkAir accident, I’m sure they would have been disabled before the dive.
That is true for the MI185 case, the flight path was very well defined and it was difficult to replicate it. Other steep descents in the 30-50 degree range have occurred for other causes, the trim runaway being a low likelihood cause (except when someone does something pretty dumb with a system architecture unwittingly).
The data gives enough information to exclude most stalls as a cause, and a number of items can give a roll excursion that will drop the nose to below 30 degrees nose down in short order. The contenders for that sort of thing is a simple TS entry and disorientation, a slat element extension at cruise, a TR deployment, a revisit of the yaw damper/rudder reversal issue etc. Most of these are not likely but they get to the same point in time and space without being MI185 or EGYPT 990, or really odd events like Adam Air 574.