What happened
On June 29, 2014, a Zlin Z-142 was performing a takeoff roll on runway 11 at the EPKC aerodrome. After reaching rotation speed, the aircraft lifted off but did so at a high angle of attack, causing it to sink back onto the runway pavement. The pilot immediately reduced engine power and applied the brakes. The aircraft came to a stop before the end of the runway and subsequently taxied to its parking position.
Prior to the takeoff, the aircraft's takeoff weight was determined to be 352.2kg, representing 97% of its maximum allowable weight, with a cabin load of 190kg. While the engine test at the runway threshold showed correct parameters and the flaps and trim were set for takeoff, the pilot did not calculate the density altitude for the flight. The takeoff was conducted following a previous ultralight aircraft departure.
The investigation
The investigation examined the environmental conditions, the aircraft's weight and balance, and the takeoff technique. Investigators analyzed the atmospheric data, noting a temperature of 27°C and a density altitude of 2330ft. The investigation also looked into the engine's supercharger engagement and the wind conditions during the takeoff roll.
Findings
- The aircraft was operating at a near-maximum takeoff weight during high ambient temperatures.
- The takeoff occurred during conditions of shifting winds, with the wind direction changing from 110 to 290 degrees along the runway approximately 30 seconds after the preceding aircraft had departed.
- The pilot rotated at approximately 80 km/h; however, under these specific conditions, the takeoff roll should have been extended on three wheels until reaching approximately 100 km/h before initiating rotation.
- There was a possibility of imprecise supercharger engagement, although no mechanical issues were noted in previous or subsequent flights.
- A successful takeoff had been performed earlier that same day under similar temperatures, but with a single occupant, which may have contributed to the different performance characteristics experienced during this event.