What happened
On August 3, 2010, a HOAC DV 20 Katana, registration PH-MFT, was conducting a private pilot license flight test at Teuge Airport. The flight involved a student pilot and an examiner. During the landing phase on runway 27, immediately after the main landing gear contacted the runway, the aircraft began experiencing intense vibrations.
As the student pilot attempted to initiate a go-around by applying full power, the vibrations worsened significantly. To maintain control and mitigate the risk of fire from potential sparks caused by metal-on-asphalt contact, the examiner took control, reduced power, and steered the aircraft off the runway into the grass. While taxiing on the grass, the nose gear broke off, causing the aircraft to come to an abrupt halt with its nose on the ground. Both occupants escaped the heavy damage to the aircraft without injury.
The investigation
The investigation focused on the source of the intense shaking and the failure of the nose gear. Investigators initially considered a nose wheel shimmy as the cause. However, physical evidence suggested a different origin. A piece of the propeller was recovered approximately 200 meters from the final resting position, near the area where the vibrations first began.
Examination of the engine revealed that the engine mounts were severely damaged, with several rubber mounts destroyed or missing, indicating the engine had been subjected to extreme mechanical stress. The investigation also ruled out a bird strike or ground contact, as the remaining propeller blade was undamaged and no debris or organic matter was found on the blades or the runway. A technical inspection of the propeller by the manufacturer found no manufacturing or material defects, noting that the wood fibers had pulled apart longitudinally rather than breaking at an angle.
Findings
- The primary cause of the intense vibration was the failure of one propeller blade immediately following the landing.
- The loss of the blade created a significant imbalance that transmitted heavy forces through the propeller shaft to the engine mounts.
- The sudden loss of the nose gear occurred while the aircraft was taxiing on the grass, leading to the aircraft's nose-down position.
- The specific mechanism that caused the propeller blade to separate from the hub could not be determined.