Jetstar 1329 (C140)
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 15; Flight Crew Total 20000; Flight Crew Type 2000
Other / Unknown; Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Loss Of Aircraft Control
Flight Crew Became Reoriented; Flight Crew Regained Aircraft Control; Flight Crew Returned To Clearance
Aircraft; Human Factors
The Captain leaves flight station to go the lavatory. FO flying. For unknown reason; autopilot disconnects when captain is in the back of the cabin. FO does recover from unusual attitude when he receives airplane attitude nose low and left bank 45 degrees. Captain back to flight station; FO calls Center and advises of situation. Airplane is then hand-flown to resume altitude and route. AP is checked and reengaged and monitored closely until the end of the flight. No other discrepancies or autopilot problem were encountered thereafter. Aircraft lost approximately 3;000 feet in the process. During and prior to the event; the Captain had left the flight deck and FO was flying (monitoring Autopilot coupled flight at FL360) and programming the FMS when the autopilot disconnected and the aircraft rolled off into a diving left banked descend; losing 3;000 feet before the FO could recover. In retrospect; FO should have delayed diverting attention to the FMS until both pilots were at the flight station. A normal recovery from the unusual attitude was made and reported to ATC.
Jetstar First Officer experienced an unnoticed autopilot disconnect at FL360 with the Captain in the lavatory. The aircraft is recovered from a 45 degree bank at FL330 and ATC is advised. The autopilot is reengaged and functions normally for the remainder of the flight.