Date: 201501
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Horizontal Stabilizer Trim
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Fuel Issue
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Declared Emergency; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft; Weather
Primary problem: Aircraft

Narrative: With very strong headwinds forecast enroute and with weather at our destination and our two alternates barely above minimums; we were watching fuel closely and keeping constant contact with our dispatcher. Almost halfway through our 6-hour flight we received a message from dispatch telling us we had to stop for fuel and could not continue on. After initially changing our destination to Airport ZZZ1; it was determined that turning around and diverting to Airport ZZZ offered us many more options once we landed. After landing at Airport ZZZ; it was determined that our flight attendants were out of duty period and with no Flight Attendants (FA) replacements available in Airport ZZZ the entire crew was given rooms at the airport hotel and the entire crew was assigned the follow-on flight the following morning after minimum rest. The flight departed and we were back on our way. At FL360; mach .80; and 2 hours and 20 minutes into flight the STAB OUT OF TRIM LIGHT illuminated. The Captain (CA) ran the QRH checklist for 'Stabilizer Out of Trim'. After disengaging autopilot and autothrottle; the checklist asks if 'Stabilizer Trim Responds to electric trim inputs.' After testing the control column trim switches multiple times both nose up and nose down; only once out of the five or six inputs did the trim wheel move. I don't remember which direction it responded to the input the one time it did respond; but it was determined that the electric trim inputs were definitely not responding appropriately. We also noted that no circuit breakers were popped. The last step led us to the 'Electric Stabilizer Trim Inoperative' checklist. Running this checklist had us 'cutout' both stab trim switches and disengage the disconnect clutch by having both pilots turn the manual trim handles. It was noted that significantly greater force was needed to trim nose down than was needed to trim nose up; but it was possible to trim the aircraft in both directions. The checklist then prepares you to plan for a flaps 15 approach and landing and explains that whether or not you have manual trim; elevator control would be sufficient to safely land the aircraft regardless of the stabilizer position. At this point we advised ATC that we were no longer RVSM compliant (no autopilot available) and were permitted to remain at FL360 for a while longer. The CA then began to coordinate with dispatch where we would land and Airport ZZZ2 was chosen. ATC had us descend to FL280 and flight characteristics all appeared normal throughout this descent. The CA and I discussed that in order to ensure that we were not given multiple restrictions on final (i.e. 'maintain 250 KIAS until 7-mile-final' or some other workload-increasing restriction) that it was in our best interest to [advise] ATC and we relayed the appropriate information (fuel remaining; etc.). A short time later while preparing for the approach to Airport ZZZ2 we received word from the company that Maintenance Control was concerned with the difficulty we had with trimming nose down and wanted us to land sooner rather than later so we changed our destination to Airport ZZZ3 which was about 60 miles in front of us. We prepared for the arrival and approach and referenced the non-normal landing performance pages; and then completed the deferred items in the Electric Stabilizer Trim Inoperative checklist. While slowing for the approach and before intercepting the glideslope; several times the trim was manually trimmed nose up without problem and the flaps 15 landing was completed uneventfully.




Synopsis: B737 First Officer describes a diversion for fuel due to strong headwinds on a transcontinental flight; which then requires a layover due to FA duty limits. The flight departs the next morning and again has to divert for failure of the electrical stabilizer trim control.