Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance
Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action
Procedure; Human Factors; Aircraft
After departure aircraft was being hand flown and trimming normally. Early in the climb the 'speed trim fail' illuminated momentarily then extinguished. This happened two more times. I was the pilot monitoring and reviewed the QRH procedure just in case. We continued to an initial altitude of FL330. At that point the auto pilot failed to engage and the 'speed trim fail' light illuminated and stayed on. We descended to FL270 to comply with non-RVSM requirements and informed ATC while attempting to contact dispatch. Dispatch sent us a new flight plan showing arrival fuel of 4.4. The ride was fairly bumpy and the [destination] weather was not optimal in case of a diversion. We had just flown over [an airport] where the weather was mostly clear. We coordinated with dispatch and diverted. Upon reaching the gate maintenance was standing by as required. After a lengthy system test; all checked normal. Maintenance had discovered that the stab trim cutout for the auto pilot trim was in the 'off' position. Both guards were down with the main electric trim switch was in the on or normal position even though both guards were down. The plane had come from the hanger after completing a PCU (Power Control Unit) replacement. Switches were not placed back to the normal positions per their checklist. Further; during the pre-flight check the first officer missed that the switches were not in their normal 'on' position. I had failed to notice the guards in the wrong position as well. Lesson learned; take a little extra time pre-flighting especially coming from the hanger. Supplemental note in QRH about checking that both trim cutout switches are in the proper position.
As the FO (First Officer); I was flying. Takeoff and initial climb was normal. Soon however; the yellow 'Speed Trim' light came on. After a few seconds; the light went out. This happened three times during climb. The QRH was referenced and the procedure for a Speed Trim light instructed us to 'Continue Normal Operations'. At approximately 17;000 ft.; I attempted to engage autopilot B. It would not engage. No warning lights were on at this time. I attempted to engage autopilot A and both CWS (Control Wheel Steering) systems. None would engage. Trim was operating normally. We stopped climb at FL270 letting ATC know we were now non RVSM compliant. We got a new flight plan showing us landing with 4;400 lbs of fuel; well below acceptable mins. In addition; we factored in that we would be flying through some significant weather with no autopilot. At that point; the Captain decided to divert. We coordinated with ATC and landed without incident. Maintenance met us at the aircraft and proceeded to complete their autopilot checks. The mechanic found the Autopilot cutout switch in the cutout position. After completing maintenance checks on the system; the system passed the tests. The aircraft had just gone through some maintenance operations on the yaw damper system. Maintenance personnel informed us that as part of their procedure; the Autopilot cutout switch should have been placed back to normal following the yaw damper maintenance. Nonetheless; I missed that the switch was in the cutout position during my pre-flight check. After maintenance cleared the aircraft; we proceeded without incident. Change Speed Trim procedures to check the autopilot cutout switch.
B737-800 Flight Crew reported a speed trim light indication and an inoperative autopilot during climb. Fuel concerns; weather; and the inability to operate in RVSM airspace prompted the crew to divert. Maintenance discovered that the Autopilot cutout switch was in the cutout position and had been missed during the preflight inspection.