Flight crew reported autopilot issues caused uncommanded aircraft movements resulting in deviations of course and altitude. The flight crew continued to the destination airport and turned the aircraft over to maintenance.
Synopsis
Flight crew reported autopilot issues caused uncommanded aircraft movements resulting in deviations of course and altitude. The flight crew continued to the destination airport and turned the aircraft over to maintenance.
Narrative
While in cruise flight at FL 410 the Autopilot started a quick uncommanded bank and started to descend. I quickly took over and corrected the bank and started climbing back to 410. We had lost approximately several hundred feet with a TA (Traffic Alert) and ATC advising that other aircraft were below and close to us. After getting the situation under control I advised ATC we had an Autopilot malfunction and seem to have it under control. I reengaged AP and it seemed to be normal for a few minutes; then again started an uncommanded climb. Again I took over manually and made the corrections. We asked for lower and after several minutes we're given FL270.Once at FL 270 the Autopilot was reengaged and flew for approx another 40/45 minutes without incident. As we started the GPS approach into ZZZ it failed to capture the final approach course and again I had to hand fly the approach. Once on the ground Maintenance and Chief Pilot were called and it was decided to ground the plane. This plane has been in shop for Autopilot issues several times in the past; but never to the point of a pilot deviation at Altitude. Most Autopilot anomalies have occurred either on takeoff or on an approach. Every time the plane went into the shop for an Autopilot malfunction we were told it could not be duplicated.
Second reporter narrative
I was the Second in Command (SIC) on this flight. While at FL410 in smooth air with the Autopilot engaged the plane started banking descending turn without warning. The Autopilot was in NAV and ALT mode. The Pilot in Command (PIC) immediately grabbed the controls and started to pull up and reduce the bank angle. All this happened within seconds. After disengaging the Autopilot and climbing back to alt and back on course; we lost approximately several hundred feet of altitude and went off the airway. Once back on airway and ALT; We informed ATC that we had an Autopilot issue and had rectified it. The PIC re-engaged AP and it appeared to be working fine. After several minutes it appeared to start deviating from the route and ALT. Once again; the PIC grabbed the controls; hand flew it back on course; and asked ATC for lower ALT. After descending to FL 270 we again reengaged AP and it flew well till the approach at which time it would NOT capture the final approach course on the GPS approach even though it was programmed and indicated on the scoreboard. The PIC hand flew the approach without further incident. Once on the ground; We notified Maintenance and the Chief Pilot of the issue; and the aircraft was grounded at the present location pending Maintenance. This aircraft has had several issues with the Autopilot doing strange unwanted things while in flight. It has been in the shop several times for this same issue; other Pilots have complained about it as well; every time we were told: It can't be duplicated. This is the first time it has happened at FL 410.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.