Hi,
STS
The system automatically controls the trimming trim in manual flight, without autopilot is STS = speed trim system.
It is active 10 seconds after takeoff, between 100 kts and Mach 0.60 (then 0 and 0.68 M) when the autopilot is not engaged and is made for light offs, rear centering and high engine thrust.
Its purpose is to trim the aircraft with the stabilizer when the aircraft speed varies to return the aircraft to its original speed and flight toiled.
Example, if the speed decreases, the stabilizer trim moves to sting to force the plane to recover the speed at which it was slaved correctly
So .. I dunno if the STS played a role in this crash