Date: 202103
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Aircraft: B737-900
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class B ZZZ
ATC / advisory: TRACON 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); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Time Pressure; Troubleshooting
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During cruise STAB OUT OF TRIM light illuminated intermittently.  Complied with STAB OUT OF TRIM QRH procedure.  Maintenance notified via ACARS. Descending with autopilot and autothrottle on; aircraft did not level off at the preselected 4;000 feet.  I disconnected the autopilot and autothrottle and began to return to 4;000 feet.  I tried the electric trim and found it to be inoperative.  I notified the Captain of the inoperative electric trim.  The Captain tried his electric trim and also found it to be inoperative. Captain conferred with me about disconnecting the STAB TRIM CUT OUT switches.  I agreed and the STAB TRIM CUT OUT switches were disconnected.  Captain opened the QRH and we complied with the STAB OUT OF TRIM QRH procedure.  The STAB OUT OF TRIM QRH procedure directed us to the STABILIZER TRIM INOPERATIVE procedure; which we complied with.  I tried to operate the manual trim with my left hand could not move the trim wheel through a full rotation.  I notified the Captain of this and he tried the manual trim.  Captain seem to require both hands to operate the manual trim.  Captain notified ATC and we requested delay vectors. We requested the longer Runway of XXR.  We performed a flaps 15 landing on XXR.  Descended below assigned altitude of 4;000 feet due to malfunctioning elevator trim.


Second narrative: This report is being submitted to cover the altitude deviation on approach into ZZZ. The altitude deviation was a direct result of a malfunction of the stabilizer/stabilizer trim system. The other required category reports will be covered in a separate irregularity report.Approximately two hours after departure and level at FL350; the STAB OUT OF TRIM (amber) light illuminated. We ran the STABILIZER OUT OF TRIM QRH procedure. Autopilot B was engaged and remained engaged while the light was eliminated; the aircraft maintained altitude and airspeed in light mountain wave and light chop conditions. Since the auto pilot appeared to be trimming the aircraft normally and in accordance with QRH; we continued normal operation. We notified maintenance control and Dispatch via ACARS and made a maintenance logbook entry for the condition. Dispatch acknowledged receiving the message. The light remained illuminated for approximately 10 mins. During this time both the first officer and myself reviewed not only the QRH; but Stabilizer Trim Inoperative QRH procedure in the event that these stabilizers stopped trimming at some subsequent point. We also reviewed be available information in both the flight handbook as well as the systems handbook.The STAB OUT OF TRIM light continued to illuminate intermittently in durations that ranged from several minutes to just a few seconds. We also climbed to FL370 with no abnormal indications and with the B autopilot remaining engaged. I observed some movement of the trim wheel at various times.During the cruise portion of the flight; the light was extinguished most of the time; but we did have the intermittent illuminations periodically. We informed dispatch and maintenance control that the light was illuminating intermittently.On the arrival into ZZZ we were given several intermediate level offs as well as crossing altitude and airspeed restrictions all of which were met with autopilot B engaged.While being vectored around some weather; for a visual approach to Runway XXL; we were kept somewhat high on the profile and were in a fairly aggressive dissent to 4;000 feet.  Autopilot B remained engaged throughout this descent. At 4;000 feet the flight directors commanded a level off but the aircraft continued to descend below 4;000 feet and did not capture the altitude; the first officer (pilot flying) immediately disengaged the auto pilot and auto throttles and began to correct The flight path; but due to the out of trim condition of the stabilizer the aircraft descended to approximately 3;500 feet before being able to level off the aircraft with considerable back pressure on the yoke.We informed ZZZ Approach that we had a stabilizer issue and were attempting to correct back to 4000 feet. They directed us to maintain 3000 feet. At about this time; the first officer informed me that 'I don't have any trim' and I saw him activate the yoke stabilizer trim switches for nose up and nose down trim with no movement of the stabilizer trim wheels. I attempted to trim the stabilizer using the yoke switches on my side with no effect as well. The first officer was holding a great deal of back pressure on the yolk and stated 'I need nose up trim' at this point with his concurrence after having verified that neither yolk could trim the stabilizer electrically; I selected both stabilizer trim cut out switches to cut out.At this point I told the first officer that he was going to continue to be the pilot flying and also have the radios while I reviewed the QRH procedures. After I verified that we had accomplished all of the steps and had been directed to the next QRH section. Well I was reviewing the QRH procedures the first officer attempted to trim the aircraft manually and stated 'I can't move the wheel'. It was at this point I believe where I [requested priority] with approach and told them that we had a stabilizer trim failure and we were attempting to trim the aircraft manually we requested and receiveda vector to do this and we reported our souls on board as well as fuel and requested ARFF assistance at the airport. At this point I attempted to trim the stabilizer nose up manually from my side but was unable to turn the stabilizer trim wheel. I directed the first officer to attempt to slow the aircraft to clean maneuver speed in an attempt to unload the stabilizer so that we could trim the aircraft manually. At some point approaching clean maneuver speed I was able to begin moving the trim wheel nose up but it was still quite difficult and required a significant two-handed effort to move the wheel at all. I managed to get several turn nose up trim and the first officer said 'that's good'. At this point; we were in a more or less in trim condition at clean maneuver and clean. We continue to execute QRH and requested the longer Runway (XXR). It was at about this point I believe that I informed the flight attendants of our situation and that we would be landing in about 5 to 10 minutes; to expect a normal landing but that there would be fire trucks standing by.We completed QRH and had a normal flaps 15 landing on Runway XXRWe rolled out normally and cleared the runway and informed ground control and the ARFF captain that we did not require any further assistance.We taxi to the gate and shut down the aircraft; debriefed the flight attendants; and spoke with maintenance on the ground about our situation.


Synopsis: B737-900 flight crew reported Stab Trim failure resulted in an altitude overshoot and limited control ability.