L2022-03 Separation of Passenger Door on Instructional Flight East of Pori on August 19, 2022

The passenger door of a Diamond DA42 airplane became unlocked soon after takeoff on an instructional flight from Pori aerodrome on August 19, 2022. While the crew members were attempting to lock the door, it separated from the airplane. The airplane remained controllable and returned to land at Pori without further incident. The four-seat airplane carried a flight instructor and two students.

Because the students had logged only a few flights on the airplane type they had not developed a routine in door closing and locking. Furthermore, since the door locking mechanism was operated simultaneously from the cabin and outside the airplane, task-sharing was unclear.

Unlocking was noticed by the rear seat occupant. Crew members responded promptly and instinctively to the unexpected situation and attempted to lock the door. The fact that unlocking was noticed visually and not from a warning triggered by the alerting system contributed to the crew's omission to action the relevant checklist. System warnings cue crew members to checklist execution and thereby to a predetermined course of action.

Because the fully locked condition cannot be positively verified by checking door handle position visually or from warning indications, it is easy to leave the door only partially locked.

Even though several in-flight door unlocked events on the DA40 and DA42 have been reported worldwide, airplane operators and flight crew members have remained unaware of locking-related issues. Modifications and checklist updates have failed to solve the problem, to which also the European Union Aviation Safety Agency (EASA) responded in 2011. The monitoring of the effectiveness of corrective actions in safety-critical matters has been inadequate.

The Safety Investigation Authority of Finland issued four safety recommendations with the aim of avoiding similar incidents and mitigating resulting damage.

Monitoring of Effectiveness of EASA Airworthiness Directives

• It is recommended that EASA monitors and ensures that the actions prescribed in its airworthiness directives has the adequate and desired effect.
  

• It is recommended that Diamond Aircraft Industries modifies the door locking mechanism to allow operators to achieve and verify the fully locked condition without undue difficulty. The warning system should also alert the crew members if the door is not fully locked.
  

• It is recommended that EASA ensures that type certificate holders regularly notify operators of any recurrent or serious safety findings related to applicable aircraft types.

• It is recommended that Diamond Aircraft Industries as the type certificate holder ensures that the warning labels, flight manual instructions and procedures for the DA40 and DA42 contain sufficient information that enables the operator to carry out proper actions and take particular care when opening and closing the passenger door.