The commercial pilot reported that the accident flight was the first flight in the experimental, amateur-built, tailwheel-equipped Tuttle BDK Carbon Concepts since he had completed building it.
He added that, shortly after departure, while in level cruise flight, he heard a loud “pop” and immediately saw that the left wing’s leading-edge slat had buckled and distorted, which made the airplane difficult to control.
While maneuvering for an emergency landing, the pilot had to make significant power adjustments to maintain control.
After making a right turn to begin the approach to the airport, the right wing’s leading-edge slat failed, which resulted in an almost complete loss of airplane control.
Subsequently, he guided the airplane to an open road near Wasilla, Alaska, using the rudder and varying the engine power settings. The plane hit the top of a tree before hitting the road in a nose-low attitude, which resulted in substantial damage to both wings and the fuselage. The pilot was seriously injured in the crash.
Each wing was equipped with three carbon fiber leading-edge slats located center, inboard, and outboard. A detailed examination of the airframe and engine revealed that the right wing’s leading-edge slats exhibited features consistent with compression failure of the leading edge, trailing edge bond failure, lack of adhesive in the joints, and ply bridging.
In addition, the right inboard slat attachment bracket exhibited deformation patterns consistent with an overload failure.
The left wing leading edge slats exhibited no leading-edge damage but had signatures consistent with resin starvation.
In addition, the left attachment bracket between the inboard and center slats exhibited features consistent with an adhesive failure in the joint and a disbond at the attachment.
Microscopic examination of the attachment bracket revealed a lack of adhesion, improper surface preparation, and improper adhesive thickness.
Probable cause: The structural failure of both wings’ leading-edge slats, which resulted in a loss of airplane control.
NTSB Identification: ANC16LA068
This September 2016 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.