What happened
On June 20, 2007, a Rockwell 690A Turbo Commander, registration OH-UTI, was performing an aerial photography flight when the pilot noticed the nose gear failed to lock in the down position while approaching Helsinki-Vantaa Airport. Following standard checklists, the pilot attempted to cycle the landing gear several times, but visual confirmation via the propeller hub indicated the nose gear remained partially extended.
The pilot requested and received clearance to land on runway 33 at Helsinki-Vantaa. During the landing roll, the nose of the aircraft descended, coming to rest on the partially extended nose wheel. The incident resulted in minor damage to the aircraft, including bent nose gear doors and broken antennas, but no injuries were reported to the two occupants.
The investigation
The investigation focused on the mechanical failure of the nose gear steering cylinder. Investigators discovered that all four mounting bolts for the steering cylinder had sheared off, causing the cylinder to detach from its mounting. The cylinder remained held only by the hydraulic hoses and the piston mounting bolt. During the gear extension sequence, the displaced cylinder moved behind a linkage bracket, physically preventing the gear from reaching the locked-down position.
Further examination of the aircraft's history revealed that on June 17, 2007, the aircraft had been moved at Helsinki-Malmi Airport using a tow bar attached to the hitch of a van. During this maneuver, the angle between the tow bar and the aircraft's centerline exceeded the maximum allowable 45-degree limit. This excessive steering angle forced the cylinder piston fully into the cylinder, generating enough shear force to snap the mounting bolts.
Findings
- The primary cause of the incident was the exceedance of the maximum allowable nose wheel steering angle during a ground tow operation.
- The use of a van with a tow bar attached to a hitch made it difficult for the driver to monitor the precise angle of the tow bar.
- The aircraft's nose cone lacked the required 45-degree limit markings, which had been omitted following a recent repainting of the airframe.
- An audible 'pop' was heard by ground personnel during the towing maneuver on June 17, but no corrective action was taken at that time.