Originally Posted by
MickG0105
Can somebody familiar with the Speed Trim System please comment on whether it would have been engaging and disengaging if the aircraft accelerated and decelerated through 300 KIAS. Thanks.
From the MAX FCOM 9.20.8:
Speed Trim System
The Speed Trim System (STS) is a speed stability augmentation system designed to improve flight
characteristics during operations with a low gross weight, aft center of gravity and high thrust
when the autopilot is not engaged. The purpose of the STS is to return the airplane to a trimmed
speed by commanding the stabilizer in a direction opposite the speed change. The STS monitors
inputs of stabilizer position, thrust lever position, airspeed and vertical speed and then trims
the stabilizer using the autopilot stabilizer trim. As the airplane speed increases or decreases
from the trimmed speed, the stabilizer is commanded in the direction to return the airplane to the
trimmed speed. This increases control column forces to force the airplane to return to the trimmed
speed. As the airplane returns to the trimmed speed, the STS commanded stabilizer movement is
removed.
STS operates most frequently during takeoff, climb and go-around. Conditions for speed trim
operation are listed below:
• STS Mach gain is fully enabled between 100 KIAS and Mach 0.60 with a fadeout to zero by Mach 0.68
• 10 seconds after takeoff
• 5 seconds following release of trim switches
• Autopilot not engaged