Trimmable Horizontal Stabilizer

Question 1

How is the Trimmable Horizontal Stabilizer (THS) normally operated in flight?

Answer 1

• The flight control computers control trim functions automatically.

Question 2

If no hydraulic power is available, what is the impact on the THS?

Answer 2

• The THS requires hydraulic power from the GREEN or YELLOW systems in order to function.

Question 3

If possible, how can the THS be positioned after a complete flight control computer failure occurs?

Answer 3

• Mechanical trimming is possible by manually positioning the pitch trim wheel.

Question 4

Explain what would happen if a pilot were to reach down and move the pitch trim wheel when all systems are working normally.

Answer 4

• The trim will can be turned manually. However, manual inputs have priority over computer inputs, so the autopilot would disconnect (if engaged).

Question 5

What happens to the THS after landing?

Answer 5

• The trim automatically resets to zero.