What happened
During a flight in the vicinity of California City, California, a glider sustained substantial structural damage while operating at an altitude of approximately 17,500 feet MSL. The pilot initially provided a verbal statement to an FAA inspector indicating that he had performed several aerobatic loops. He reported recovering to level flight when he heard loud bangs and felt severe vibration in the control surfaces.
Later, the pilot contradicted his earlier account, insisting that no aerobatic maneuvers were performed. Instead, he claimed to have encountered turbulence and flown through a rotor. Surface winds in the area were from 270 degrees at 22 knots, gusting to 28 knots, with peak gusts reaching 42 knots from 290 degrees. Standing lenticular clouds topped the mountains, and SIGMET Juliet 4 was in effect, cautioning of occasional severe turbulence below 16,000 feet MSL.
The investigation
A physical examination of the aircraft revealed wrinkles in the skin on the aft fuselage and empennage. The vertical stabilizer was deformed, and the left horizontal stabilizer and elevator had several areas of deformation. These findings were consistent with either extreme aerodynamic loading or structural failure during high-stress maneuvers.
Findings
The investigation highlighted the severe turbulence conditions present in the area, as indicated by the SIGMET and wind reports. The pilot's conflicting statements regarding the cause of the damage—whether due to intentional aerobatics or unintentional encounter with a rotor—remain unresolved. However, the physical evidence points to significant stress on the airframe.
Safety message
Pilots operating in areas with reported severe turbulence and strong winds should exercise extreme caution. Understanding the limitations of gliders in turbulent conditions is critical for safety.