Speed Trim System
The aircraft is equipped with a Speed Trim System, or STS. It is designed to improve flight characteristics during:
- Low gross weight
- Aft centre of gravity
- High thrust w/o autopilot
Its purpose is to return the aircraft to a trimmed speed by commanding the stabiliser in a direction opposite the speed change. It uses the autopilot stabiliser trim and increases control column forces to force the airplane to trimmed speeds. As the trimmed speed is returned, the STS commanded stabiliser movement is removed.
Additionally, stall control is also enhanced with the STS. As airspeed decreases, the STS will trim the stabiliser nose down.
Conditions for its operation are:
- Airspeed between 100 kts and Mach 0.60 within 10 seconds of takeoff
- 5 seconds following release of trim switches
- Autopilot not engaged
- Sensing of trim requirement
The system monitors:
- Stabiliser position
- Thrust lever position
- Airspeed
- Vertical speed
The conditions for STS operation include:
- Speed < Mach 0.68
- 10 seconds after takeoff
- 5 seconds following release of main electric stab trim switches
- Autopilot not engaged
- Sensing trim requirement