What happened
On July 23, 2001, a Beech D95A, registration SE-EEU, was conducting an IFR flight from Göteborg/Säve to Norrköping. While descending to 3,000 feet approximately 10 nautical miles south of Linköping, the aircraft experienced a sudden, heavy impact noise accompanied by violent vibrations in the right-hand engine. The failure caused an immediate loss of power on the right engine and a significant yaw and roll tendency toward the right side.
The pilot reacted by shutting down the right engine, feathering the propeller, and disengaging the autopilot. To maintain control, the pilot had to reduce power on the left engine and utilize maximum rudder and aileron deflection. The aircraft's airspeed dropped to 120 knots, and the rate of descent increased significantly. After declaring an emergency, the pilot received radar vectors to Linköping/SAAB airport, where the aircraft successfully landed despite substantial damage to the engine mounts and the nose section of the fuselage.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the wreckage and conducted metallurgical analyses of the propeller blades. The investigation focused on the right-hand Hartzell propeller, which had lost a blade. Investigators looked into the maintenance history, specifically regarding Hartzell Service Bulletin 136, and evaluated the effectiveness of existing inspection protocols for this propeller type.
Findings
- The accident was caused by the failure of a propeller blade due to a fatigue crack.
- The crack originated from an irregular groove located in the blade root guide channel.
- While all prescribed maintenance and inspections had been performed according to the aircraft's technical documentation, the investigation found that the existing inspection methods were not sufficiently reliable to detect such defects.
- The separation of the blade created massive imbalance forces, which were severe enough to break the engine mounting brackets, causing the engine to partially separate from the wing.
Safety action
To prevent similar occurrences, the SHK recommended that the Civil Aviation Administration ensure either a specific operating hour limit is implemented for this propeller type or that a more reliable inspection method is developed to monitor critical areas of the propeller blades.