BACKGROUND: The crew started the After Landing checklist when the aircraft was parked
and the engines stopped. During the After Landing check, the crew moved the horizontal
stabilizer to the “Aircraft Nose Down” (AND) position. When the stabilizer came to 4 units, it
stopped (correctly) and the Stabilizer Trim Motor could not move up or down electrically. The
problem could not be solved by telephone so Technicians flew to the station. They started the
hydraulic pumps and set the FLAP to the NOT UP position. Then the Stabilizer Trim Motor
NOTE: The movement of the Stabilizer Trim Motor depends on the Flap position.
When the Flap is:
UP – Stabilizer Trim movement is approximately 4 -17 units.
NOT UP – Stabilizer Trim movement is approximately 0 -17 units.
PROBLEM: When the stabilizer moved up (AND), a strong tailwind also moved the elevator
up (Aircraft Nose Up) (ANU). This caused the column cutout switches to disconnect the
electrical power to the Stabilizer Trim Motor.
WHAT HAPPENED: The Elevator Control Column was in the ANU position and the stabilizer
was commanded to the AND position. . Because the two commands oppose each other, the
column cutout switches disconnected the Stabilizer Trim Motor.
ACTION 1: If you think that this problem has occurred,
Start the EMDP, system A or B
The Elevator Control Column moves to the neutral position
Set the FLAP to the NOT UP position
Use the Stabilizer Trim Switches to move the Stabilizer up and down.
ACTION 2: Also, to see if the Stabilizer Trim motor operates correctly, set the STAB TRIM
OVERRIDE switch to OVERRIDE (This bypasses the column cutout switches). Use the
Stabilizer Trim Switches to move the Stabilizer up and down.
REFER TO: SDS 27-41
NOTE: This event was on a B737-6/7/8/900 but could even occur on the B737-3/4/500
because the system is similar. The B737-3/4/500 has only one control cutout switch.