How many primary trim channels exist on the longitude, and what are they labeled?

• A. One channel, A
• B. Two channels, A and B
• C. Three channels, A–C
• D. Four channels, A–D

Answer: (B)

The trim system on the Longitude is built with redundancy in mind, so there are two independent channels that control the stabilizer trim. These primary trim channels are labeled A and B. In normal operation, both channels are available to drive trim commands, which provides reliability and smooth trimming. If one channel has a fault, the other can continue to trim, and the fault is indicated to the crew. There aren’t additional primary trim channels beyond these two, which is why the correct description is two channels labeled A and B.