What is the key difference between the A/B primary pitch trim channels and the secondary pitch trim system?

What is the key difference between the A/B primary pitch trim channels and the secondary pitch trim system?

• A. Primary channels are mechanical, secondary is electrical
• B. Primary channels control rudder, secondary controls elevator
• C. Primary channels are redundant circuits to the primary motor, secondary is a completely separate pitch trim motor assembly used if the primary fails
• D. Primary channels are for roll, secondary for pitch

Answer: (C)

The key idea is how pitch trim is implemented for redundancy. The A/B primary channels are two electrical paths that command the same primary pitch trim motor, giving you two chances to keep trimming if one path or its wiring has a fault. The secondary pitch trim system, however, is a completely separate motor assembly with its own circuitry, designed to take over if the primary motor or its circuits fail. This keeps the aircraft trimable even in a failure of the primary system. So, the difference isn’t about rudder versus elevator or about a roll/pitch split; it’s that the primary channels provide dual-path control to the same motor, while the secondary system is an independent, backup motor configured to operate separately.

The key idea is how pitch trim is implemented for redundancy. The A/B primary channels are two electrical paths that command the same primary pitch trim motor, giving you two chances to keep trimming if one path or its wiring has a fault. The secondary pitch trim system, however, is a completely separate motor assembly with its own circuitry, designed to take over if the primary motor or its circuits fail. This keeps the aircraft trimable even in a failure of the primary system.

So, the difference isn’t about rudder versus elevator or about a roll/pitch split; it’s that the primary channels provide dual-path control to the same motor, while the secondary system is an independent, backup motor configured to operate separately.