witness mark

witness mark (plural witness marks)

1. A scratch or similar mark on each portion of an assembly used to determine the previous position or location of its parts.
   • 2001 March 27, National Transportation Safety Board, “1.16.3 Detail Examination and Tests of Standby Rudder Actuator Input Shaft and Bearing”, in Aircraft Accident Report: Uncontrolled Descent and Collision With Terrain, United Airlines Flight 585, Boeing 737-200, N999UA, 4 Miles South of Colorado Springs Municipal Airport, Colorado Springs, Colorado, March 3, 1991‎^[1], archived from the original on 8 May 2022, page 64:

     During the examination, the bearing was reassembled into the actuator body so that the fire witness marks on the actuator surface and the bearing flange matched and the bearing was situated as close as possible to the actuator's housing surface. In this position, it was noted that an additional 30-degree rotation was required in order for the bearing flange to mate against the actuator boss.