AUTOTRIM
The purpose of the automatic trim (AUTOTRIM) function is to keep the
average position of the output shaft of the roll, pitch and yaw linear actuators
near center to ensure optimum Linear Actuator authority in response to
aircraft control commands; the AP Autotrim function commands the Trim
Actuators to achieve that.
The Autotrim function on each axis is active when either or both Autopilots
are engaged in ATT mode and the relevant axis Force Trim is engaged.
The Autotrim control reference is the Linear Actuator displacement from the
center: when the displacement exceeds a percentage of the Linear Actuator
stroke, the Trim Motor is commanded at an appropriate rate in the direction
to re-center the Linear Actuator (different percentage values are set for pitch,
roll and yaw axes).
TRIM PRIORITY FUNCTION (TRIM MASTER)
The Trim Priority Function has the purpose to provide and retain the Trim
Master operation on controlling the Trim and Collective actuators.
For normal operation, when both autopilots are engaged, the autopilot that
was engaged first retains the Trim Master function.
The indication of what AP is elected as Trim Master is shown in the Flight
Controls synoptic page of the MFD.
As the Trim Master AP is disengaged (either manually or automatically due
to a failure), the remaining AP is elected Trim Master.
The Trim Master function switching logic is overridden if one or more linear
actuators fail.
A set of relays in the aircraft wiring are used to ensure that only the Trim
Master AP provides commands to the pitch, roll, yaw and collective trim
actuators so that they cannot be corrupted by the other AP.
Similarly, the trim end-around feedback is provided to identify trim and
collective actuator movement and direction.
PRE-FLIGHT TEST (TEST)
Pre-flight test allows verifying autopilot control and monitoring functionality.
During the pre-flight procedure, as part of the System Checks, pilot is
required to perform the AFCS TEST that is initiated by pressing the TEST
button on the Autopilot Controller with the following conditions:
• Aircraft on the ground (WOW)
• Electrical and hydraulic power available
• Autopilots disengaged
• Hands off the flight controls (Force Trims on)
• Collective down (