What happened
On December 28, 2018, a Learjet 31A was operating an instrument flight rules (IFR) positioning flight from London Biggin Hill, United Kingdom, to Faro, Portugal. The aircraft was configured for ambulance service and carried a crew of two pilots and two company employees, with no passengers on board.
While descending through approximately 11,500 ft Pressure Altitude in Portuguese airspace, the pilot in command (PIC) proposed performing a roll around the aircraft's longitudinal axis. Although the co-pilot explicitly expressed disagreement with the maneuver, the PIC disconnected the autopilot at approximately 13,200 ft and took manual control.
At approximately 11,37 UTC, the crew executed two steep turns with bank angles of roughly 140 degrees to the left and right. Following these turns, the PIC initiated a controlled roll at 11:38 UTC. The maneuver began at an indicated airspeed of approximately 301 kt IAS and concluded at 251 kt IAS. During the execution of these maneuvers, the aircraft experienced a maximum vertical acceleration of 2.47 g. The aircraft landed safely in Faro later that morning without any injuries to the crew or damage to the airframe.
The investigation
The BFU investigation was prompted by the airline's Flight Data Monitoring (FDM) program, which identified the event in May 2019 due to unusually high roll angle data. The investigation utilized Flight Data Recorder (FDR) data provided by the operator, as the Cockpit Voice Recorder (CVR) data was no longer available at the time of the report.
Technical inspections of the aircraft following the event revealed no structural damage, though investigators noted that the elevator push/pull rod ends required replacement. The investigation also reviewed the airline's operational manual, which explicitly prohibited aerobatic maneuvers and specified that intentional stalls were prohibited above 18,000 feet with flaps or gear extended.