What happened
On September 11, 2024, an Embraer-550 Praetor 600, registration 9H-MFX, was performing a commercial flight departing from Runway 12 at Stockholm/Bromma Airport. Shortly after rotation and lift-off, the flight crew received a warning indicating a failure in the Flight Control System. This was immediately followed by a rapid and unexpected upward pitch movement that exceeded the crew's expectations.
As the aircraft climbed, the pilot attempted to counteract the pitch using the control stick, but found that the control authority was significantly limited. To stabilize the aircraft and stop the continued climb, the pilot had to utilize the manual pitch trim to adjust the horizontal stabilizer angle. The crew declared a Mayday, and air traffic controllers provided vectors for an approach and landing at the departure airport once the system functionality was restored. There were no injuries to the five persons on board and no damage to the aircraft.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the aircraft's flight recorders, including the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR), and conducted simulator reconstructions of the event. The investigation focused on the Flight Control System (FCS) behavior and the technical conditions leading to the system degradation.
Investigators found that the aircraft's Flight Control Computers (FCC) experienced a simultaneous reset. This caused the FCS to transition into a simplified "Direct Mode." During this transition, the stabilizer ceased its automatic trimming functions, leaving the aircraft in an untrimmed state relative to the increasing airspeed. Testing by the manufacturer later successfully reproduced this fault under specific conditions involving the TTP bus systems.
Findings
- The primary cause of the sudden pitch was a fault that triggered a reset of both Flight Control Computers immediately after takeoff.
- This reset forced the Flight Control System into Direct Mode, which prevented the stabilizer from automatically adjusting for the changing airspeed.
- The resulting out-of-trim condition was so severe that the pilot had to use nearly full control stick input and manual trim to maintain the commanded pitch.
- The crew's previous familiarity with a similar event involving the same aircraft type in August 2024 helped them react intuitively and manage the emergency effectively.