ERA22LA427 · Northwing Design APACHE SPORT

The pilot and passenger were in cruise flight about 3,500 ft mean sea level (msl) flying offshore between 55 and 60 mph in the weight-shift-control (WSC) aircraft. The passenger reported that the pilot informed him that the flight might encounter turbulence, then about 5 minutes later, it felt like, “something punched the plane,” consistent with turbulence. The passenger reported that he then noted 8 of the right wing ribs were extending 3 to 4 inches aft of the aft edge of the wing sail, and the fabric of the right side of the wing was no longer stretched and the right wing area was much smaller than the left wing. He then felt an upward jar, and the aircraft entered a right descending turn that the pilot attempted to control. When “very close to the ocean,” he felt a force consistent with activation of the airframe parachute. After water impact, he struggled but managed to release his restraint and remained in the water about 30 minutes before being rescued. Examination of the wing, which washed ashore several months after the accident, revealed that the outer portion of the sail fabric on the right side of the wing had moved inboard along the leading edge tube and bunched at the juncture of the leading edge tube and wing strut. The inspection did not determine the condition of the ribs on the right side of the wing. The resulting fabric movement, combined with the passenger-reported displacement of multiple wing ribs, likely changed the airfoil shape and lift properties of the right side of the wing, resulting in the right descending turn described by the passenger. Although there was no structural failure of the right wing, it could not be determined why the sail moved inboard along the leading edge tube or what ribs were remaining with the wing and the rib positions among the sail. While the passenger reported experiencing turbulence immediately before the observed wing issue, the available weather data did not support conditions conducive to turbulence, and no cumulus clouds were visible on satellite images or in the dataset around the accident time. Additionally, the passenger’s description of the airframe parachute activation occurring “very close” to the surface of the water suggested that it may not have been activated with sufficient time to fully realize the benefits of such a system.

Verbatim NTSB analysis and probable cause from the NTSB dataset