On May 9, 2021, the pilot (and owner) of the TERCEL gyrocopter arrived at EPTO – Pomeranian Aeroclub’s aerodrome to perform a recreational flight. The pilot performed a preflight check in accordance to the Flight Manual. No technical irregularities were found at that time.
At about 9:53 hrs UTC the pilot took off and then made a flight in the EPTO zone at an altitude of about 2400 ft. During the return flight to EPTO, when the gyrocopter was above a dense, high forest, the pilot noticed vibrations of the fuselage. According to the pilot’s assessment, the vibrations gradually increased, therefore, he reduced the engine speed to the minimum in order to relieve the gyrocopter structure. At the same time, he began descending to 1400 ft , and chose the shortest way to the aerodrome. The pilot informed the Aerodrome service by radio about the emergency and asked for priority to land with any course, and immediately received clearance to land and was informed about the current wind direction. After reaching the altitude of 1400 ft , the pilot increased the engine speed to a value that guaranteed a level flight. After another 30 seconds, there was a sudden shock and a very strong increase in vibration of the entire gyrocopter. The pilot immediately shut down the engine and the vibrations stopped. Then the pilot turned off the main electric power switch, closed the main fuel valve and informed the aerodrome about the emergency landing in the forest.
The gyrocopter with the engine turned off abruptly lost speed, so the pilot performed a dive to gain speed and chose to land near the railway line crossing the forest. According to the pilot, it was the only place in this area that allowed for an emergency landing. Despite the limited manoeuvrability of the diving gyrocopter, the pilot managed to fly over the treetops. Before the touchdown, the tips of the main rotor blades collided with tree trunks and the power line located in the area of the landing site. Then, the gyrocopter touched down on the main landing gear on the north-west side of the railway track. During the touchdown, the left wheel of the main landing gear hit the granite post. As a result the landing gear was torn out and the fuselage turned to the left and the gyrocopter overturned to the right side. The rotating rotor hit the ground, causing blades, mast and rear tail destruction.
After the occurrence, the pilot left the wreckage unaided through the right door, without injuries, and then informed (via phone) the Pomeranian Aero Club, emergency services and PKBWL about the accident. The ambulance service arrived at the site and examined the pilot, and the fire brigade extinguished a forest litter fire, initiated by the broken power line.
The direct cause was detachment of one the three blades of the Kašpar Ka-2/3-LT rear propeller used in the gyrocopter.
Root causes:
− improper material used for the propeller manufacturing – material prone to brittle fracture;
− inadequate design of the propeller blade mounting part – sharply intended mounting thread and a recess for the grub screw of the blade-nut joint.
Safety recommendation 2021-1048-1
The Investigation of the accident showed that the material and design solutions applied in the Kašpar Ka-2/3-LT propeller did not ensure its adequate strength and were the cause of the occurrence.
Therefore, PKBWL has proposed the following safety recommendation:
It is recommended that the manufacturer of the Kašpar Ka-2/3-LT propeller considers the necessity of introducing changes in the material and design solutions leading to an increase in the durability of the Kašpar Ka-2/3-LT propeller blades to the necessary level.
