Narrative:

At a cruise altitude of FL400 ATC advised traffic would cross overhead 1;000 feet above from right to left. The aircraft crossed exactly over us. The co-pilot was watching the plane fly over and disengaged the autopilot while leaning forward to watch the aircraft go over. The disengaged tone went off immediately I was watching the plane as well and it took a moment to notice why it disengaged. The co-pilot didn't say he did it just looked at me then after a few moments said it was him. It had surprised him as well. I reached up and pushed the autopilot button within 15 seconds of disengage but after pushing the button I did not verify on the pfd that it engaged. The airplane was trimmed for that altitude already so it seemed it was on. I then looked back out the window (side). Approximately 3 to 5 minutes later ATC gave us a frequency change. I noticed the airplane in a very slight descent and turn; ATC also noticed at that time as well. This was a center controller approximately 80 NM north of lszh. I slowly started bringing the airplane back to where it should be. Probably too slowly. At this point we were 15-20 degrees left of course and 300-500 ft low. When the controller asked why we were turning and descending the co-pilot didn't respond right away. He didn't know and as I was correcting I didn't say the autopilot was off. As soon as I noticed I should have said something to him. His delay in responding to the controller then resulted in the controller again asking what we were doing in a more panicked tone. The co-pilot I think was waiting for me to be back on heading and altitude to respond instead of just saying what we were doing. I should have responded myself as I was correcting when he didn't. My slowness to correct and his delay in response got the controller worried something was wrong. There was another crewmember in back and I didn't want to just jerk it back on course at FL400. But I should have reacted faster. We apologized to the controller when handed off and they said no problem. Everything would have been fine if I would have verified the autopilot was engaged. Not pushing the buttons hard enough on proline 21 aircraft and verifying it engages is a common mistake I should have caught. The buttons do not illuminate in any way showing mode selected is activated. You must look at the pfd and verify which I didn't.

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Original NASA ASRS Text

Title: RA390 Captain reports autopilot becoming disengaged at FL400. Autopilot engage button was not pushed firmly enough to reengage and not confirmed on the PFD. Altitude and track deviations occured.

Narrative: At a cruise altitude of FL400 ATC advised traffic would cross overhead 1;000 feet above from right to left. The aircraft crossed exactly over us. The co-pilot was watching the plane fly over and disengaged the autopilot while leaning forward to watch the aircraft go over. The disengaged tone went off immediately I was watching the plane as well and it took a moment to notice why it disengaged. The co-pilot didn't say he did it just looked at me then after a few moments said it was him. It had surprised him as well. I reached up and pushed the autopilot button within 15 seconds of disengage but after pushing the button I did not verify on the PFD that it engaged. The airplane was trimmed for that altitude already so it seemed it was on. I then looked back out the window (side). Approximately 3 to 5 minutes later ATC gave us a frequency change. I noticed the airplane in a very slight descent and turn; ATC also noticed at that time as well. This was a Center Controller approximately 80 NM north of LSZH. I slowly started bringing the airplane back to where it should be. Probably too slowly. At this point we were 15-20 degrees left of course and 300-500 FT low. When the Controller asked why we were turning and descending the co-pilot didn't respond right away. He didn't know and as I was correcting I didn't say the autopilot was off. As soon as I noticed I should have said something to him. His delay in responding to the Controller then resulted in the Controller again asking what we were doing in a more panicked tone. The co-pilot I think was waiting for me to be back on heading and altitude to respond instead of just saying what we were doing. I should have responded myself as I was correcting when he didn't. My slowness to correct and his delay in response got the Controller worried something was wrong. There was another crewmember in back and I didn't want to just jerk it back on course at FL400. But I should have reacted faster. We apologized to the Controller when handed off and they said no problem. Everything would have been fine if I would have verified the autopilot was engaged. Not pushing the buttons hard enough on Proline 21 aircraft and verifying it engages is a common mistake I should have caught. The buttons do not illuminate in any way showing mode selected is activated. You must look at the PFD and verify which I didn't.

Data retrieved from NASA's ASRS site as of April 2012 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.