Incident Overview
On 9 January 2016, during a pre-flight inspection of a SZD-50-3 Puchacz glider at Rudniki airfield (EPRU), cracks in the paint were observed on the lower surfaces of both wings near the airbrake boxes. The glider, registered as SP-3288, was operated by Aeroklub Częstochowski. The last flights prior to the discovery took place on 31 December 2015, when the ambient temperature was approximately -15°C. No damage was noted during the pre-flight inspection before those flights.
Investigation Findings
A detailed examination of the glider revealed that the wing spars were not whitened, indicating no structural overload. On 18 February 2016, a workshop inspection was conducted at Wirkk Serwis Szybowców. After removing the paint and filler layers, it was determined that the cracks were confined to the paint layer and did not extend into the fiberglass laminate. In one location, after paint removal, the laminate structure appeared potentially compromised, although this was likely unrelated to the paint cracks formed during flight.
Cause
The cracks on the lower wing surfaces most likely formed during the aerobatic maneuvers performed on the last flight day. Low ambient temperature, which reduces paint elasticity, may have contributed to the cracking.
Actions Taken
The incident was scheduled for discussion at the mandatory Flight-Technical Conference of Aeroklub Częstochowski, which is a prerequisite for flight clearance in 2016. No preventive recommendations were issued by the investigation commission. During the inspection discussions, it was noted that paints used on gliders performing aerobatics should be more elastic. The commission also reminded that the maximum rough control speed for the SZD-50-3 Puchacz is 150 km/h and its permissible speed is 215 km/h, emphasizing attention to speed and control deflections during aerobatics.