Piper PA 12 N4018H accident near Skwentna, Alaska

Probable cause

The pilot's failure to properly secure the external load, which resulted in the load shifting during flight, interference with the water rudder cable, and a subsequent loss of control

NTSB analysis

The pilot was transporting about 120 lbs of plywood, secured to the airplane's float struts via cargo straps, to his remote cabin. The pilot reported that, about 200 ft above the ground during the landing approach, the airplane experienced an uncommanded left turn, then the pilot realized that he had no rudder control and that the rudder was "locked to the left." The airplane subsequently impacted trees and terrain. The pilot reported no mechanical anomalies with the engine and no anomalies with the airplane before the loss of control.

The airplane's water rudder cables descend from the fuselage along the support struts to which the plywood was secured. The water rudders were directly linked to the rudder. It is likely that, during the flight, the plywood shifted and interfered with the water rudder cable, which resulted in the pilot's loss of rudder control during the landing approach.

Text from the NTSB. Open the NTSB docket for ANC17LA033 for the full record.