Falcon 20FJF/20C/20D/20E/20F
Flight Crew Multiengine; Flight Crew Flight Engineer; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 100; Flight Crew Total 21000; Flight Crew Type 800
Troubleshooting; Workload
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Loss Of Aircraft Control
Flight Crew Returned To Clearance; Flight Crew Took Evasive Action; Flight Crew FLC Overrode Automation; General Maintenance Action
Aircraft
Cruising at FL340 on autopilot; suddenly aircraft rolled up to 60 degrees of bank and began a descent in excess of 2;000 FT per minute before we could recover control. Altitude deviated down to FL330 with a subsequent recovery to FL340. [We] immediately advised Center of an autopilot hard over with the altitude deviation. Upon recovery; Center asked if we could maintain RVSM and we responded yes; but after further consideration decided that we should not continue in RVSM and requested a descent out of RVSM airspace. We were cleared to FL280 and continued to our filed destination without further incident. I wrote up the autopilot as INOP; canceled the remainder of the flights; spoke to our Maintenance; and deferred the autopilot to fly manually to home station at FL250; flying off autopilot. I am unaware of any traffic conflict at this time and was not advised by ATC that there had been a traffic conflict. The jet is now in maintenance (troubleshooting the problem).
The reporter stated that the aircraft's Mechanic determined the only component in the system which could cause an upset such as this would be the autopilot amplifier. That component was changed; the autopilot run continuously on the ground for a full day with no anomalies and so; deemed airworthy. The reporter has since flown the aircraft numerous flights with no problem.The upset developed very rapidly and resulted in a 4;000 FPM rate of descent. During the recovery G's were pulled; but not what he would consider excessive.
A Falcon 20 autopilot amplifier malfunctioned at FL340 which resulted in a rapid roll to 60 degrees; and a 1;000 FT altitude loss. The flight descended out of RVSM airspace for the remainder of the flight.