Accident Details
On June 17, 2017, about 1434 Alaska daylight time, a float-equipped Piper PA-12 airplane, registration N4018H, was destroyed when it impacted trees and came to rest in an open meadow near Skwentna, Alaska. The commercial pilot, who was the sole occupant, was uninjured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as an external cargo load operation.
Flight and Circumstances
According to the pilot, the purpose of the flight was to transport plywood to his cabin located off Indian Creek, a tributary of the Yentna River, approximately 14.5 miles southeast of Skwentna. About 120 lbs of plywood was secured with various cargo straps to the struts connecting the floats to the fuselage. The airplane was approaching to land to the south on a north-to-south oriented waterway. The pilot reported a light wind from the south. While about 200 ft above the trees, the airplane made an uncommanded turn to the left. The pilot did not recall the airspeed at the time. He applied left rudder but received no response, and the rudder was described as "locked to the left." Unable to maintain control, the airplane struck trees and came to rest in an open meadow. The pilot egressed without further incident.
Mechanical and Load Information
The pilot reported no preimpact mechanical malfunctions or failures with the engine or airframe prior to the uncommanded left turn. The plywood, secured to the float struts, was angled to follow the downward angle of the struts. The floats were Edo 089-2000 type. The water rudder cables descend from the fuselage along the support struts to which the plywood was secured, and the water rudders are directly linked to the rudder. The airplane's gross weight and center of gravity for the accident flight could not be determined.
External Load Operations
FAA Order 8400.34 outlines a comprehensive process for conducting external load operations under Part 91 or Part 135, including aircraft eligibility, inspection, and issuance of a Special Airworthiness Certificate and operating limitations. The pilot stated he had an external load permit on file with the FAA and had been conducting external loads with the accident airplane for several years. However, a review of FAA records revealed no external load permit for N4018H; the pilot previously held a permit for a Cessna A185F airplane. FAA Order 8400.34 also notes that plywood installed as an external load is considered a major alteration to the airframe and discusses the aerodynamic effects of external loads on handling, stability, and control.