CRJ-200 flight crew reported autopilot malfunction in cruise flight resulted in the airplane pitching up followed by a TCAS RA.
Synopsis
CRJ-200 flight crew reported autopilot malfunction in cruise flight resulted in the airplane pitching up followed by a TCAS RA.
Narrative
While in cruise at FL310 ATC advised us of crossing traffic; the First Officer (FO) and I both had the traffic in sight and the FO reported that to ATC. We then returned to our conversation while monitoring the traffic. We were flying with the auto pilot on and normally operating we suddenly and abruptly had an autopilot disengagement. As soon as the autopilot disengaged the airplane pitched up rather aggressively and started to climb. By the time I said autopilot disengage and got on the controls the airplane was already climbing at greater than 1200 FPM. This aggressive pitch then; nearly immediately after; caused a TCAS RA with another airplane. The FO reported the TCAS RA to ATC immediately and was giving excellent correcting call outs throughout the RA. I was fighting to get the airplane back into the green RA box by arresting the climb and beginning a descent. I believe we had gained approximately 400 ft. above FL310 at the highest point. The total duration of the event was approximately under 1 minute. After getting the clear of conflict call from the TCAS we were close to our original altitude and we returned to FL310 and reported to ATC that we were clear of the conflict and level at FL310. We also reported that we experienced an issue with our autopilot which caused the RA to ATC. Once level we attempted to re-engage the autopilot which did not work initially but did on the second attempt. The auto pilot functioned normally for the remained of the flight. There is little if anything to improve to prevent this due to the randomness of the autopilot disengagement. While flying in RVSM airspace there is simply less time for altitude deviations before they will set off a TCAS RA. It is not normal procedure to be actively shadowing the controls while in cruise with the auto pilot on.
Second reporter narrative
While in cruise at FL310 we were advised of traffic passing above and opposite direction. I advised ATC we were 'looking.' The Captain and I both saw the other aircraft due to the contrails it was making. Having the traffic insight and being no factor the Captain and I resumed our conversation while keeping the traffic in sight. Approximately a minute after the autopilot disengaged. The Captain called 'auto pilot disengage' while saying that we received a TA/RA to descend. I looked at the VSI which was indicating 1200 FPM climb the Captain was actively pushing the yoke down. I then looked to make sure I could still see the traffic; which was still above us. I advised ATC we had a TA/RA and were descending. We got clear of conflict and leveled back at FL310. We then were able to reengage the autopilot. I notified ATC we were back level at 310 and had an autopilot disengagement but appeared we had it reengaged. The event took a total of no more than a minute from autopilot disengagement; TA/RA; corrective action; back to level off at FL310. This event to me seemed to happen exactly as it does in the sim and the Captain and I reacted as taught. I felt our communication and coordination as a crew was exactly what we needed to do. The Captain acted promptly and effectively. The only way the Captain could have reacted any faster was like how it happens in the sim where you are on guard and actively shadowing the controls. Which during this phase of flight and this altitude it's not required to shadow the controls.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.