B737 MAX 8
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Loss Of Aircraft Control
Flight Crew Executed Go Around / Missed Approach; Flight Crew Overcame Equipment Problem; Flight Crew Regained Aircraft Control
Aircraft
On descent to [destination]; I was the flying pilot. Autopilot tripped off and lost attitude information on Captain's side. Gave aircraft to FO as his attitude information was reliable. I started into the QRH looking for a checklist dealing with loss of attitude; heading; etc. I had a difficult time finding the correct checklist so I decided to hit recall and see if that would lead me to the right direction. It had an IRS message which led us to see the IRS 1 Fault. Now I was able to execute the correct checklist procedure for the IRS FAULT on the MAX aircraft. Per checklist we were allowed to use the autopilot on the right side and continued descent. I had attitude information back but did not have a full flight director. The FO continued to fly as his flight director was reliable. Checklist called for autopilot off for the approach. We were set up to fly the RNAV. Just prior to reaching [an enroute waypoint]; I noticed the STABILIZER OUT OF TRIM light on. I directed the FO to turn off autopilot since it had to be off for the approach anyway. When he disconnected the autopilot; the aircraft was trimmed heavy nose down resulting in descent. We lost VNAV so we asked to abandon the approach and were given a heading and altitude to fly. Because of the out of trim situation; the FO was having a difficult time controlling the aircraft. Not knowing what exactly was going on; I [advised ATC] and our attention was focused solely on flying the plane. Airspeed trended up and down rapidly but I don't believe it was ever in danger of being slow or fast but took rapid and immediate corrective actions. Eventually aircraft control was stabilized and correctly trimmed and a return to the airport continued without the use of the autopilot. This time we elected to fly the [other approach] knowing that we did not need VNAV. The FO did a great job hand flying the approach and we executed a normal landing.This event was somewhat confusing at first because I had a difficult time finding the correct check list. Then we were both uncertain as to why the aircraft got out of trim while flying on the autopilot without the autopilot disconnecting. I do not know if the issues are related or a separate event. It would be nice to know. The FO was surprised at the out of trim forces on the aircraft after the autopilot was disconnected and struggled momentarily to regain a stabilized trimmed aircraft. Since I did not know the forces he was experiencing; all I could do to help was monitor aircraft flight and call out deviations from normal.We discussed the first chain of events which was the autopilot disconnecting and the lack of attitude information on the Captain's side. It took some time to determine the cause and the correct checklist to execute. We don't believe it resulted in a master caution light which would have directed us to the cause. Doing the recall; did finally alert us to the problem. I don't know for certain if we got the master caution and if it was pushed out too early before analyzing the situation. It's possible but we didn't think that happened. We also don't know if these events are related and if the QRH needs to be modified.
Reporter stated the aircraft was a B737 MAX 8.  No feedback from company on root cause.  Reporter expressed concern that the autopilot did not disconnect sooner; allowing the out-of-trim condition to go beyond normal parameters; resulting in abnormally high control forces to overcome the out-of-trim condition.
#1 IRS FAULT right before top of descent. Captain transferred aircraft control to me; and ran QRH checklist. As Pilot Flying now and still working Radios I handle Center requests; advise of equipment failure; meet crossing restriction and continue down to I believe 11;000 [ft]. Listening to Captain reading checklist; [approach] setup; I was assuming unable RNP not usable due to equipment limitation of IRS FAULT (not resettable in air.) In terminal area; we decide to try RNP as there was no note in checklist about approach type limitation. Also try autopilot; and CMD B does engage. Plan is now to disengage autopilot; as prescribed in QRH; before commencing approach. Descend from about 11;000 to 3;000 using CMD B autopilot; checklists were complete; everything was green. ATC advises us there is a strong crosswind of 50 kts; and to plan for it. I believe we were configured to flaps 10 and 170 kts as we received the approach clearance; maintain 3;000 until established; cleared RNP. In the turn we are going to be turning the autopilot off shortly; and receive a STAB OUT OF TRIM light. We both agree to turn autopilot off; and I turn the autopilot off. The airplane is heavy; and trimmed nose low. I commence correcting the undesirable attitude; trimming; and then adding power gradually. We lost 200-300 feet; but went back up to 3;000 in short order. Airspeed still not increasing as fast as I like so I push the power way up; and get a desirable trend. In the time between turning the autopilot off; and returning to 3;000 feet we lost approach vertical guidance. Advise the captain we need to go around; get us some vectors out of here. Captain advises ATC; we get vectors; settle everything down; setup for the [approach]; and return to land without incident. Airplane handled just fine with the autopilot off; and after trimming.The QRH did not mention that the autopilot stabilizer trim would fail to be able to keep up with demand; or at all during an IRS FAULT (assuming ADIRU/FCC failure as well?) It only mentioned that the autopilot should not be used during approach; which it was not. Assuming that the VNAV approach guidance quit because I descended below the path (which I am not proud of having let happen) when the autopilot was disconnected; and the stabilizer was in a nose down trim condition; and VNAV didn't disconnect/quit because we were shooting an RNP approach with a single IRS; then I guess not having an approach type limitation isn't necessary in the QRH checklist for IRS FAULT notes? Previous flying experience and experience in the simulator training I had for stabilizer malfunction was good enough to keep me from panicking as I was able to trim; and just added power; and knew we could just fly away. Had I known to EXPECT or been forewarned of the potential that stabilizer trim would be so out of sorts; I may have been much more aggressive in my control of aircraft attitude; and would not have had to jockey the power. The airplane did not seem like it was flying out of trim in the moment when CMD B autopilot was on. I am quite familiar with this airspace; the MSA; and the approach into ZZZ; and that I am glad something like this didn't happen to a crew with 15-20 flying miles to go.Experience. Better systems knowledge. Afterwards I read there are different types of IRS systems on the 737-8; besides just the difference between them; and the B737NG.
B737 MAX 8 Captain reported landing safely following loss of IRS 1 that manifested as multiple system failures; including autopilot 1 and Captain's attitude information. Autopilot 2 was engaged but allowed an out-of-trim condition to develop; resulting in control difficulties.