What is a jackscrew ?
I see now. I knew what a jackscrew was, but not related to airplanes. See quote below. It seems jackscrew are part of large airplanes trim.
aspx) NTSB said, "Alaska Airlines flight 261 accident was the loss of airplane pitch control resulting from in-flight failure of the horizontal stabilizer trim system jackscrew assembly's acme nut thread.
Alaska Airlines Flight Collides With Truck In Boston Airport