Narrative:

Climbing en route from las with passenger aboard we were assigned FL350. The autoplt was engaged for a hands-off climb out of approximately FL250 and the automatic leveloff/altitude pre-select was set for FL350. ATC called out opposite direction traffic at 12 O'clock position and FL370. We told ATC we had the traffic in sight before the autoplt 'event' occurred. As the aircraft approached FL350 in a hands-off mode, the autoplt abruptly disengaged (neither pilot touched any controls to cause the disengagement), and the aircraft went into a sharp climb. I immediately grabbed the yoke to arrest the climb, but, in the interest of passenger comfort, I did not 'push over' or 'bank over' aggressively. We climbed to approximately 35800 ft before a correcting descent was achieved. The actual disengagement of the autoplt was an alarming physically uncomfortable jolt. ATC gave us a phone number to call upon landing at sfo. I discussed the matter with the supervisor on duty and explained the situation. He has submitted a report to the las vegas FSDO.

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Original NASA ASRS Text

Title: GULFSTREAM, G2, FLC OVERSHOT ASSIGNED LEVELOFF ALT DUE TO AUTOPLT DISENGAGEMENT CAUSING LOSS OF SEPARATION WITH ANOTHER ACFT.

Narrative: CLBING ENRTE FROM LAS WITH PAX ABOARD WE WERE ASSIGNED FL350. THE AUTOPLT WAS ENGAGED FOR A HANDS-OFF CLB OUT OF APPROX FL250 AND THE AUTO LEVELOFF/ALT PRE-SELECT WAS SET FOR FL350. ATC CALLED OUT OPPOSITE DIRECTION TFC AT 12 O'CLOCK POS AND FL370. WE TOLD ATC WE HAD THE TFC IN SIGHT BEFORE THE AUTOPLT 'EVENT' OCCURRED. AS THE ACFT APCHED FL350 IN A HANDS-OFF MODE, THE AUTOPLT ABRUPTLY DISENGAGED (NEITHER PLT TOUCHED ANY CTLS TO CAUSE THE DISENGAGEMENT), AND THE ACFT WENT INTO A SHARP CLB. I IMMEDIATELY GRABBED THE YOKE TO ARREST THE CLB, BUT, IN THE INTEREST OF PAX COMFORT, I DID NOT 'PUSH OVER' OR 'BANK OVER' AGGRESSIVELY. WE CLBED TO APPROX 35800 FT BEFORE A CORRECTING DSCNT WAS ACHIEVED. THE ACTUAL DISENGAGEMENT OF THE AUTOPLT WAS AN ALARMING PHYSICALLY UNCOMFORTABLE JOLT. ATC GAVE US A PHONE NUMBER TO CALL UPON LNDG AT SFO. I DISCUSSED THE MATTER WITH THE SUPVR ON DUTY AND EXPLAINED THE SIT. HE HAS SUBMITTED A RPT TO THE LAS VEGAS FSDO.

Data retrieved from NASA's ASRS site as of July 2007 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.