Cessna 525B N869AC accident near Gulf Of Mexico, GM

Probable cause

The separation of the left wing extension and winglet for reasons that could not be determined based on the available evidence.

NTSB analysis

The business jet was equipped with wing extensions (via supplemental type certificate) that included winglets and wing extension-mounted aerodynamic control surfaces that automatically deployed to counteract measured structural loads. Before the airplane’s descent from flight level (FL) 310, the weather was clear with no turbulence. When the airplane was descending through FL 300 for FL 270, the pilot felt “two jolts of sudden turbulence” that he described as a negative G followed by a significant positive G twice in the span of about 1 second. The pilot noted that the airplane was yawing, and he subsequently observed that the left winglet had separated, resulting in substantial damage to the airplane. He declared an emergency and landed without further incident at a nearby airport.

Review of automatic dependent surveillance-broadcast and GPS revealed that, during the airplane’s descent, its airspeed was slightly outside the airplane manufacturer’s maximum operating speed (VMO/MMO) performance envelope. At the time of winglet separation, the airplane was descending about 5,300 ft per minute at 275 knots calibrated airspeed.

Eleven days after the accident, the separated winglet was recovered from the Gulf of Mexico; however, the section of the left wing extension that included the aerodynamic control surface was not recovered. Metallurgical examination of the recovered components revealed overstress features and no evidence of fatigue. Additionally, systems testing of the aerodynamic control surface control units, the system computer, and the enhanced ground proximity warning system revealed no anomalies. Because the aerodynamic control surface on the left wing extension was not recovered, the reason for the left wing extension and winglet separation could not be determined.

Text from the NTSB. Open the NTSB docket for ERA23FA174 for the full record.