Co-pilot door failure leads to engine damage during takeoff

Casualties unknown • Peterborough/Sibson Airfield, Cambridgeshire, GB

A Let 410 aircraft experienced a serious incident at Sibson Airfield when an unsecured co-pilot's door detached during takeoff, striking the propeller and engine.

What happened

On 20 June 2008, a Let 410, registration HA-YFC, was performing an aerial work flight for a parachuting group near Sibson Airfield, Cambridges．brimshire. The aircraft was carrying one crew member and five passengers. Following takeoff, the co-pilot's door/emergency exit unexpectedly opened and was pulled from its hinges. As the door departed the aircraft, it struck the right engine nacelle, the right propeller, and the fuselage. Despite the impact, the pilot managed to perform an immediate return to the airfield, completing an uneventful landing. There were no fatalities and no injuries among the occupants, though the aircraft sustained damage to the right propeller, nacelle, and co-pilot's door.

The investigation

The investigation established that prior to the flight, the co-pilot's door had been left open to allow an engineer to perform a routine pre-flight inspection. Because the pilot arrived late, the engineer performed the walk-around on the pilot's behalf. Although the door appeared closed, the primary locking mechanism had not been properly engaged.

Investigators examined the door and its mounting structure, finding no mechanical failure in the latching mechanisms. The investigation also noted that the cockpit handles for the door are difficult to see because they are painted the same color as the surrounding structure. Furthermore, while a warning light exists for the rear fuselage door, there is no separate warning light for the co-pilot's door when the rear door is already open. This lack of a distinct alert meant the pilot, who expected a warning light due to the open rear door, was not alerted to the unlocked co-pilot's door.

Findings

  • The co-pilot's door was left unlocked following maintenance/inspection tasks.
  • The door locking handles lacked sufficient visibility within the cockpit.
  • The pilot was not alerted to the unlocked co-pilot's door because the existing warning light system does not provide a discrete alert for that specific door when the rear fuselage door is also open.
  • The secondary internal latch requires the primary lock to be engaged in order to function correctly.

Probable cause

The incident was caused by the co-pilot's door being left in an unlocked state following a pre-flight inspection, compounded by a lack of visual conspicuity of the locking handles and the absence of a specific cockpit warning for the co-pilot's door when the rear door is open.

Frequently asked questions

What happened in the 2008-06-20 Let 410 accident near Peterborough/Sibson Airfield, Cambridgeshire, GB?

A Let 410 aircraft experienced a serious incident at Sibson Airfield when an unsecured co-pilot's door detached during takeoff, striking the propeller and engine.

What aircraft was involved and where did it happen?

The accident on 2008-06-20 involved a Let 410, registration HA-YFC, at Peterborough/Sibson Airfield, Cambridgeshire, GB.

What was the probable cause of the accident?

The incident was caused by the co-pilot's door being left in an unlocked state following a pre-flight inspection, compounded by a lack of visual conspicuity of the locking handles and the absence of a specific cockpit warning for the co-pilot's door when the rear door is open.

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