Saturday, May 18, 2019

737 Pitch Trim Incidents

Pitch trim is an abstract term to represent the ability to reduce column forces by moving the stabilizer and elevator. This post will dwell on stabilizer trim. 

All airplanes provide at least two means to trim the stabilizer, mostly using two seperate actuators motors. Except the Boeing 737, which relies on manual trim as the second actuator. 

The only stabilizer trim incident of interest that I can find (searching NTSB database) for 737 involved a jammed actuator and that the pilot was UNABLE to trim the stabilizer, due to clutch issues. 

Ethiopian ET302 encountered high opposing forces due to the mistrim; it has been assumed that the ET302 actuator was not jammed, and there has been no concern raised that the ET302 clutch would have oppressively opposed trimming manually, on top of the aero loads.

Thursday, May 16, 2019

The Beat Goes On

On Wed, May 15, House Transportation and Infrastructure Committee, Aviation Subcommittee convened a Hearing with the NTSB and FAA regarding 737 MAX airworthiness.  Information was provided, that which was new, still confusing, important, repeated, wrong, left out, and offensive.