What happened
On April 13, 2013, at approximately 09:10 UTC, a highly experienced professional test pilot took off from a private airfield in Chojne, near Sieradź, Poland, to conduct a flight test program for a newly constructed Dedal-KB ultralight, registration SP-SWKB. After takeoff, the pilot established contact with the airfield owner and later notified Warsaw FIS of the intention to perform climb tests up to FL090.
During the flight test, at approximately 09:44 UTC, the pilot initiated a controlled descent on a heading of 207 degrees to accelerate the aircraft. During this phase, the aircraft reached a true airspeed of approximately 230 to 234 km/h, which exceeded the aircraft's maximum permissible speed (VNE). As the pilot attempted to recover from the descent, the structural integrity of the aircraft failed. The aircraft began to disintegrate in mid-air, with debris and the pilot falling into forested and agricultural areas near Redzeń Drugi. The pilot, despite being equipped with a functional parachute, was ejected from the cockpit at an altitude too low to deploy it effectively.
The investigation
The PKBWL investigation examined the aircraft's flight history, the pilot's qualifications, and the physical wreckage. The investigation focused on the aircraft's structural limits, the accuracy of the airspeed instrumentation, and the flight test procedures being followed. Investigators analyzed radar data from various sectors, which showed the aircraft's radar echo splitting into multiple fragments just before the signal disappeared.
Findings
- The primary cause of the accident was the aircraft reaching a true airspeed exceeding the VNE during the accelerated descent, which, when combined with the pull-up maneuver, generated aerodynamic loads that exceeded the structural strength of the airframe.
- The aircraft's airspeed measurement system had not been calibrated prior to the flight tests, leading to understated airspeed indications.
- The flight tests were being conducted in a manner inconsistent with the safety principles established in the flight test program.
- The pilot's death was exacerbated by the fact that he was not wearing a protective helmet.
- The pilot's parachute was technically functional and capable of deployment, but the low altitude of the ejection prevented its use.