What happened
On October 8, 2019, a scheduled commercial flight from Münster/Osnabrück to Stuttgart experienced a serious malfunction during takeoff. The crew, consisting of a highly experienced Line Training Instructor and a relatively inexperienced copilot on his first supervised flight, was operating a BAe Systems Jetstream 3200.
During the takeoff roll, the aircraft reached a speed of approximately 130 kt before the pilot in command (PIC) initiated an aborted takeoff. As the aircraft approached decision speed (V1) of 108 kt, the copilot attempted to rotate the aircraft but found the flight controls were blocked. The aircraft drifted to the right, crossing a taxiway and exiting the runway pavement. The excursion resulted in no injuries, though the aircraft sustained light damage, and a runway light and a sign were damaged. The aircraft eventually returned to the apron.
The investigation
The BFU investigation focused on why the flight controls were immobile despite the takeoff attempt. Investigators examined the cockpit voice recorder (CVR) and flight data recorder (FME), which revealed that the crew had failed to properly execute the line-up checklist. Specifically, the crew bypassed the flight controls check and failed to verify the stall protection system.
Technical examination of the aircraft revealed that the gust lock lever was in the locked position. Crucially, investigators discovered a mechanical defect: a bent connection in the push rod assembly allowed the engine power levers to be advanced beyond the flight idle position even while the gust lock was engaged. This defect bypassed the mechanical safety feature that should have prevented a takeoff with the controls locked.
Findings
- The primary cause of the excursion was the engaged gust lock, which rendered the flight controls immobile during the rotation attempt.
- A mechanical failure in the gust lock mechanism allowed the engine throttles to be advanced while the controls were locked.
- The crew experienced self-imposed time pressure due to a delayed departure slot, leading to rushed procedures.
- The airline's abbreviated checklists lacked a specific requirement to verify the gust lock was released and used less stringent terminology for control checks.
- There was a significant disparity in experience between the instructor and the copilot, which hindered effective Crew Resource Management (CRM).
Safety action
The BFU recommended that EASA transform the manufacturer's highly recommended Service Bulletin (SB 27JM-5350) into a mandatory Airworthiness Directive to ensure the gust lock mechanism functions correctly on all Jetstream 3100/3200 aircraft.