Narrative:

As I walked down the jetbridge; I saw (2) maintenance personnel standing there with the aircraft logbook. (For ease of understanding the maint personnel will be referred to as a and B). I also saw the first officer (first officer) standing there with them. I inquired as to what was going on as I had looked at the MEL dashboard for my tail no. And had only seen nonessential equipment and furnishings (nefs). The maint personnel told me that they were filling out a parts work order document for a part that was installed on the aircraft earlier that day and that it would be completed very soon. I let them continue. I proceeded into the aircraft and conducted the brief with my crew who were all present as they had flown in earlier in the day. The flight attendants (fas) were already aware of the nefs. Right as I was about to finish my brief; I noticed that passengers had begun boarding. I quickly got into the cockpit and began my preflight duties. Aircraft was on gpu power when I entered. I then noticed that we had an EICAS caution msg 'stabilizer lock fault'. Maintenance was finishing up their documents and were in the cockpit at the time. I immediately pointed out the EICAS msg to one of them and began to pull out the QRH. Maint a told us that the message was associated with the work they had performed earlier on the aircraft for the flight control parts and also because of the aircraft being powered up all day. Maint B was in the cockpit and he said he was on the phone with the maintenance controller; and then he proceeded to tell the maintenance controller about our EICAS msg. He then instructed us to do a power reset procedure to resolve it. Both; maintenance a and B indicated that the aircraft would need to be shut down for at least 7 minutes. I began preparations and briefed the gate agent; ground crew; passengers and flight attendants. We elected to keep the passengers on the airplane. We followed the instructions as the maint guy stayed in the cockpit. 7 minutes elapsed; and they asked us to power up the airplane. Aircraft completed its flight control tests and the EICAS message did not come back. Maint a then used my first officer's mfd to go into the diagnostic screen and check a few things and said the airplane was good to go. They left the aircraft and we proceeded as normal. Our flight was uneventful until approximately 15 mins prior to ZZZ VOR. We were at FL360 (requested higher for the bumps) when we received an EICAS caution msg - stabilizer lock fault (fail) in flight. I immediately assigned controls and communications to [the] first officer and I proceeded to run the QRH. The QRH called for us to 'land as soon as possible' and at the current position we concluded that ZZZ would be the best option as it was the closest airport. The QRH described our situation having a fluctuating nose up/nose down drift tendency due to the stab lock failure and we deemed this to be a flight controllability issue so we elected to [advise] ATC and immediately request vectors for ZZZ. We were given a left heading 230 off our course and an altitude to descend to. We elected to begin a shallow descent using vs as we still unaware of the severity of our problem. I continued with the QRH procedures and communicated with dispatch; our flight attendants; and finally our passengers. The flight attendants were briefed using the test items. I continued to let first officer fly the airplane as I was getting the mcdu setup for our return and communicating with our dispatcher simultaneously. We both were monitoring the aircraft's pitch setting at every junction of our duties and noticed that it appeared to be operating normally however when we left our cruising altitude of FL360 to begin our descent; the pitch trim setting would fluctuate back and forth from 2.7 nose up - 3.0 nose up and then back to 2.7 nose up. We monitored the changes with every pitch and power change. I then took over controls and communications around approximately 15;000 feet. We completed our descentand approach checklists while being given vectors for the ILS. We made sure not to induce any aggressive maneuvers with pitch changes during our vectors. We were given direct ZZZ on the ILS and began slowing down and configuring a little prior. As we started configuring; specifically around flaps 3; the pitch trim started to pitch up quite rapidly. The first officer called this to my attention. I noticed the same. I continued to configure on profile; with gear down and later flaps 5. I disconnected the autopilot as I noticed it trending up. The pitch trim was increasing more rapidly and reached 7.6 degrees at one point (the highest we both recall).the controls felt heavy and flying the airplane in this setting was very peculiar as I had to learn how to compensate for the trim fluctuations. The pitch trim was fluctuating during the approach and reached 6.8 at around 700 feet until the flare. I briefed that I would keep the thrust in a little longer as I was unsure to how the aircraft would pitch in flare once we reduced power. The landing was successful and uneventful; I used max reverse and brakes to bring it to a safe stop and we both determined that we would be able to taxi off the runway. We then taxied to the gate; powered down. I explained the situation to the passengers from the cabin and they were very understanding and happy to be on the ground. We then deplaned and the gate agent began working on alternative options for our passengers.

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Original NASA ASRS Text

Title: EMB-175 flight crew experienced degraded pitch control due to system failure. Flight diverted and landed without incident.

Narrative: As I walked down the jetbridge; I saw (2) Maintenance personnel standing there with the aircraft logbook. (For ease of understanding the Maint personnel will be referred to as A and B). I also saw the First Officer (FO) standing there with them. I inquired as to what was going on as I had looked at the MEL dashboard for my tail no. and had only seen Nonessential Equipment and Furnishings (NEFs). The Maint personnel told me that they were filling out a parts work order document for a part that was installed on the aircraft earlier that day and that it would be completed very soon. I let them continue. I proceeded into the aircraft and conducted the brief with my crew who were all present as they had flown in earlier in the day. The Flight Attendants (FAs) were already aware of the NEFs. Right as I was about to finish my brief; I noticed that passengers had begun boarding. I quickly got into the cockpit and began my preflight duties. Aircraft was on GPU power when I entered. I then noticed that we had an EICAS caution msg 'STAB LOCK FAULT'. Maintenance was finishing up their documents and were in the cockpit at the time. I immediately pointed out the EICAS msg to one of them and began to pull out the QRH. Maint A told us that the message was associated with the work they had performed earlier on the aircraft for the flight control parts and also because of the aircraft being powered up all day. Maint B was in the cockpit and he said he was on the phone with the Maintenance controller; and then he proceeded to tell the Maintenance Controller about our EICAS msg. He then instructed us to do a Power Reset procedure to resolve it. Both; Maintenance A and B indicated that the aircraft would need to be shut down for at least 7 minutes. I began preparations and briefed the gate agent; ground crew; passengers and flight attendants. We elected to keep the passengers on the airplane. We followed the instructions as the Maint guy stayed in the cockpit. 7 minutes elapsed; and they asked us to power up the airplane. Aircraft completed its flight control tests and the EICAS message did not come back. Maint A then used my FO's MFD to go into the diagnostic screen and check a few things and said the airplane was good to go. They left the Aircraft and we proceeded as normal. Our flight was uneventful until approximately 15 mins prior to ZZZ VOR. We were at FL360 (Requested higher for the bumps) when we received an EICAS Caution msg - STAB LOCK FAULT (FAIL) in flight. I immediately assigned controls and communications to [the] First Officer and I proceeded to run the QRH. The QRH called for us to 'LAND AS SOON AS POSSIBLE' and at the current position we concluded that ZZZ would be the best option as it was the closest airport. The QRH described our situation having a fluctuating nose up/nose down drift tendency due to the Stab Lock failure and we deemed this to be a flight controllability issue so we elected to [advise] ATC and immediately request vectors for ZZZ. We were given a left heading 230 off our course and an altitude to descend to. We elected to begin a shallow descent using VS as we still unaware of the severity of our problem. I continued with the QRH procedures and communicated with Dispatch; our Flight attendants; and finally our Passengers. The Flight attendants were briefed using the TEST items. I continued to let FO fly the airplane as I was getting the MCDU setup for our return and communicating with our dispatcher simultaneously. We both were monitoring the aircraft's pitch setting at every junction of our duties and noticed that it appeared to be operating normally however when we left our cruising altitude of FL360 to begin our descent; the pitch trim setting would fluctuate back and forth from 2.7 nose up - 3.0 nose up and then back to 2.7 nose up. We monitored the changes with every pitch and power change. I then took over controls and communications around approximately 15;000 feet. We completed our descentand approach checklists while being given vectors for the ILS. We made sure not to induce any aggressive maneuvers with pitch changes during our vectors. We were given direct ZZZ on the ILS and began slowing down and configuring a little prior. As we started configuring; specifically around Flaps 3; the pitch trim started to pitch up quite rapidly. The First Officer called this to my attention. I noticed the same. I continued to configure on profile; with Gear down and later Flaps 5. I disconnected the autopilot as I noticed it trending up. The pitch trim was increasing more rapidly and reached 7.6 degrees at one point (the highest we both recall).The controls felt heavy and flying the airplane in this setting was very peculiar as I had to learn how to compensate for the trim fluctuations. The pitch trim was fluctuating during the approach and reached 6.8 at around 700 feet until the flare. I briefed that I would keep the thrust in a little longer as I was unsure to how the aircraft would pitch in flare once we reduced power. The landing was successful and uneventful; I used max reverse and brakes to bring it to a safe stop and we both determined that we would be able to taxi off the runway. We then taxied to the gate; powered down. I explained the situation to the passengers from the cabin and they were very understanding and happy to be on the ground. We then deplaned and the gate agent began working on alternative options for our passengers.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.