Andrzej Jeziorski/WARSAW

THE POLISH AIR FORCE has grounded its PZL-Mielec I-22 and M-93 Irydas, following the accident-investigation report into a fatal crash on 24 January. It is refusing to place further Iryda orders until design improvements are implemented.

Manufacturer PZL-Mielec says that it is complying with the defence ministry Air Accident Investigation Committee's "technical and organisational" recommendations.

The air force is dismissing subsequent press reports of " secret" Committee documents, which allegedly indicate pilot error, suggesting that the published findings are a cover-up.

Industry sources say that the accident investigation has become embroiled in the long-running battle for budgetary support between Poland's two rival trainer manufacturers: PZL-Mielec and Turbo Orlik manufacturer PZL-Okecie.

The accident involved an early PZL-5-powered I-22 variant, and appears to have been caused by a fault in the trim mechanism. The Iryda is trimmed by adjusting the angle of attack of the tail-plane, and investigators say that the aircraft's tail-plane was found at an extreme angle because of a "technical fault".

Although the Committee could not establish exactly which components were to blame, the most likely cause is believed to be an electrical fault.

Investigators say that the problem may have arisen when the pilot attempted to trim the aircraft, while inverted at an altitude of 12,450ft (3,800m). The tail-plane rotated and, when the pilot rolled upright, the aircraft entered a steep dive.

Under extreme negative-G loading, the airframe began to disintegrate before impact. The pilot and instructor died.

Col Janusz Karpowicz of the Deblin pilot-training school, where the Irydas are based, criticises the aircraft. Karpowicz says that the Iryda's controls are too heavy in the longitudinal axis and that the aircraft has too high an approach speed for a trainer. He also criticises the Iryda's "poor avionics".

Source: Flight International