Fly-By-Wire (FBW) System - horizontal stabilizer movement during maintenance
Effectivity: Global 7500 aircraft
ATA 27
It has been reported to Bombardier that some Global 7500 aircraft have experienced uncommanded horizontal stabilizer trim movement during maintenance.
On the Global 7500 aircraft, the FBW System includes an Auto Horizontal Stabilizer trim function. In flight, the Auto trim function will automatically move the horizontal stabilizer to off load the elevators.
This function is inhibited during maneuvers; for example, upon lateral acceleration, large vertical accelerations, or when the high-speed protection function or the high angle of attack protection function is active.
The Auto trim function will allow trimming in only one direction to ensure that adequate pitch authority is available for recovery. The auto-stab trim is enabled within two (2) seconds after ground-air transition is detected.
The aircraft nose-up trimming is active when the aircraft is more than 50 ft. above the ground or when the elevator command reaches the minimum command limit.
The aircraft nose-down trimming is active if the aircraft speed is less than the maximum allowed trim speed (VmaxTrim) +5kt or if the elevator command reaches the maximum command limit.
Please note that putting the aircraft weight off wheels (WoffW) during maintenance may fulfil the auto trim logic and could cause the auto trim function to move the horizontal stabilizer.
To avoid any movement of the horizontal stabilizer during maintenance, it is recommended to set the following circuit breakers to out:
