What happened
During a scheduled flight from Malme Airport to Bromma Airport, the flight crew encountered unexpected flight control warnings. Prior to departure, maintenance personnel had identified damage on the left-hand airflow sensor and replaced the entire unit. While the takeoff proceeded normally, the stick shaker activated immediately upon lift-off. The crew determined this was a false warning and attempted to use the IDNT/INHIB 1 button to manage the alert, though the system did not appear to respond as expected.
As the aircraft climbed through 660 feet into cloud cover, the stick pusher activated, forcing the control column forward. The crew followed emergency checklists to shut down the affected systems, which successfully resolved the issue and allowed for a safe landing.
The investigation
SHK investigators examined the replaced left-hand airflow sensor and discovered it had been incorrectly assembled. The unit was found to be misaligned by 45 to 50 degrees across all angle readings. Because the stick shaker only requires a single sensor to indicate a high angle of attack, the faulty sensor was sufficient to trigger the initial warning. The subsequent activation of the stick pusher occurred because turbulence caused the rate of change in the remaining functional sensor to reach a threshold that, combined with the faulty sensor's data, triggered the push command.
Investigators also looked into why the error was not caught during the pre-flight maintenance. They found that after the sensor was replaced, a simplified test—intended only for vane replacement rather than full sensor installation—was performed. This insufficient testing meant the underlying assembly fault remained undetected.
Findings
- The primary cause of the incident was a confusion between maintenance instructions for the "Vane assembly" and the "Airflow sensor," which resulted in an incomplete functional test.
- The use of similar terminology for different components increased the likelihood of procedural errors.
- Interruptions occurring during the sensor replacement process acted as a stress factor that contributed to the mistake.
- A failure to perform a proper re-inspection after the component replacement allowed the faulty unit to remain in service.