What happened
On July 9, 2005, the historic Douglas DC-2, registration NC39165, was performing a ferry flight from Lelystad Airport to Den Helder Airport for an aviation open day. The flight crew, consisting of two pilots and one flight engineer, successfully completed the landing approach. After the aircraft had landed and was decelerating on the runway, the cockpit indicators signaled a critical change: the green light for the left landing gear extinguished, replaced by a red warning light, accompanied by the gear warning horn.
As the crew attempted to assess the situation and bring the aircraft to a halt, the aircraft began to tilt heavily to the left. This movement continued until the left wingtip and the rotating propeller made contact with the runway surface. The crew immediately shut down the engine to mitigate further damage. While there were no injuries to the three crew members, the aircraft sustained severe damage.
The investigation
Investigators determined that the left landing gear likely disengaged from its mechanical lock during the braking phase of the runway rollout. The hydraulic pressure within the retraction cylinder was insufficient to maintain the gear in its extended position, causing the aircraft to sink toward the left. The resistance provided by the retraction cylinder prevented a sudden collapse, which helped limit the extent of the damage.
Subsequent inspections of the aircraft, conducted after it was transported to Aviodrome in Lelystad, revealed that the mechanical locking mechanism of the left gear had been bent, and the right gear's locking mechanism also showed slight deformation. Investigators considered that the tow bar used for the main wheels might have been the source of the stress. This specific tow bar, designed for straight-line hangar movements, may have exerted excessive torsional forces on the landing gear during sharp turns.
Findings
- The primary cause of the incident was the failure of the left landing gear to remain mechanically locked during deceleration.
- The hydraulic pressure in the retraction cylinder was unable to hold the gear in the down position.
- The use of a tow bar designed for straight movements may have introduced torsional stress to the landing gear mechanisms during maneuvering.
Safety action
To prevent a recurrence, the following measures were implemented:
- The locking mechanism was upgraded to a system from a DC-3/C-47 Dakota, which includes an additional secondary lock.
- The main wheel tow bar was replaced with a version attached to the tailwheel, and procedures were updated to avoid sharp turns during towing.
- Inspection intervals were shortened, requiring a visual check of the entire undercarriage during every pre-flight inspection and a comprehensive inspection, including retraction tests, every 30 landings.
- The Aviodrome shared these findings and the upgraded solution with the Museum of Flight in Seattle, which operates the only other flying DC-2, advising them to replace their similar locking mechanism.