Gulfstream Autopilot Malfunction

[pelmet]

"The Sunwest Aviation Ltd. Gulfstream G150, C-GZCZ, was operating as flight CNK715 from Calgary, AB (CYYC) to Boise, Idaho (KBOI). During rotation, shortly after take-off on departure from Calgary, the flight crew experienced A/P Pitch Trim Fail annunciator light and disconnected the Auto Pilot. While climbing through 17 000 feet asl and 250 KIAS aircraft pitch control required full forward pressure. The flight crew declared PAN/PAN and referred to the QRH. Pitch Trim Override was selected and control of the aircraft was regained. The aircraft was vectored back to Calgary with a long approach and landed without further incident. Company maintenance found relay in # 1 pitch trim motor nose up command circuit failed in a latched position. The relay was replaced, and the system tested serviceable."

I am wondering if there is an error in this report. It says that the A/P pitch trim fail light illuminated and the autopilot was disconnected during rotation. I don't think I have ever heard of an autopilot that could be intentionally used during takeoff/rotation.

[ahramin]

During rotation, shortly after take-off

Obviously it was after take-off, not during rotation. Just a lack of understanding of aviation terminology by the person typing the report is all.

[GyvAir]

During rotation, shortly after take-off on departure from Calgary

Sounds like some confusion in writing the report.. doesn't rotation generally occur prior to take-off?
Also, if the relay failed continuously latched as stated, it shouldn't take very long before full pressure is required to counteract. I don't know how long it would take them to climb from rotation to 17,000', where it says they fully disconnected the pitch trim. Even near empty, likely longer than it would take for the pitch trim to run well into an alarming range.

Edit: ahramin beat me to it

[SgtStroka]

I just went through that scenario in the Sim, if was a full aft trim scenario, I played dumb to the sim trainer cause I could feel the wheel moving on my knee also of course the Pitch MisTrim ANN was on. However I followed the checklist (which is retarded) and gripped the controls and with all my my might had to push forward. There is NOWAY I could re trim the aircraft in that situation with one hand on the control and the other on the trim. The shortcut which wasnt in the checklist is pull the pitch trim circuit breaker, then after that I could manually reset the trim to what I thought was appropriate for that segment of flight.

Yikes.

[GyvAir]

Is there no AP/YD disconnect switch or the like that will remove power to the servo relays?

[switchflicker]

"nose up command circuit failed in a latched position."

I think the key words are failed in the latched position. No amount of power or lack thereof would rectify the problem.

Sw

[GyvAir]

I should have specified "all power" to the relay or servo. I didn't mean remove power from the relay coil circuit.

[CID]

Auto-trim and manual trim are not controlled by the same circuits. Auto-trim needs to indicate failures so that pilots have time to disengage . The basic standard (I'm paraphrasing) requires the aircraft to still be controllable after 3 seconds of trim runaway. This is more or less enough time for pilots to notice the trim fail and disengage the autopilot.

After that, depending on the problem, they should be able to correct the trim manually.

[vcollazo]

If this ever happens to you, and you're worried about being able to keep the nose down, the best technique is to roll into a 40 to 50 degree bank while you sort out the issue and pull the circuit breaker.

[xsbank]

Vcollazo, you mean ACTUALLY FLY IT?