Originally Posted by
Ian W
From Positive Rate
Interesting that there are other trim problems than MCAS for the Max8. Neither of the ASRS reports would be due to MCAS as they occurred with autopilot engaged and MCAS is disabled when autopilot is engaged.
Yes there are quite a few trim reports including numerous when electric trim is inoperable. Off the track a wee bit here, but, I found this report by a FO clearly confused by automated trim- except it's on a 737-700 in November 2017?
At the gate, I adjusted the trim setting for a flaps one takeoff. It was a normal taxi to the runway. As FO, I was the Pilot Flying. As we climbed through 400 feet AGL, I noticed the trim switch on my control wheel was not operating. I called for Heading Select as per the departure procedure and at 1000 feet AGL called for "Set Speed" and "Climb Thrust". (Still no trim response from my control wheel trim switch.) As we climbed out the "speed trim" seemed to be picking up the slack and providing adequate trimming. As I called for flaps up I expected the speed trim to stop operating and again tried to trim through use of the control wheel trim switch; still nothing. I asked the Captain to try trimming forward on his trim switch. His was also inoperative. I requested VNAV at 3000 feet AGL.
As power and speed was increased there became a pronounced nose high flight control pressure. The trim wheel continued to intermittently rotate. My thought was that the "Speed Trim" was still somehow still active and was interfering with normal trimming. I waited to see if speed trim would catch up. It did not and excessive forward control wheel pressure continued to be required to maintain 250 knots in the climb. We were then cleared to 13,000 feet. We leveled off and began to troubleshoot the problem. I asked the Captain to take the controls while I re-adjusted my seat for better leverage on the control wheel. At that point the Captain and I agreed that he would fly the aircraft and I began working the check list, radios, and we would return to the departure airport.
Although we still had reasonable control over the aircraft, I explained the problem to Approach Control and that we would need to return to the airport. I requested a straight in ILS Approach with vectors since the weather at the departure airport reported at 10 miles and 1000 feet and slight right cross-winds. I selected the ILS Approach to the departure airport as listed in the approach section of the FMS. The Captain was busy flying (without autopilot due to the trim issue) as I was setting up the radios, minimums, requesting landing information, talking to Flight Attendants and making the PA announcement that we would be returning to the departure airport; while still trying to do that "Pilot Monitoring" thing. I thought I was still in the "Green". Apparently, I wasn't.