Thorne Bay

The pilot reported that, while the float-equipped airplane was in cruise flight about 1,200 ft above ground level, the engine made a loud noise and lost partial power, so he maneuvered the airplane to land on a nearby lake. During the approach, the engine lost total power, and the airplane descended into an area of trees before reaching the lake, which resulted in substantial damage to the wings, fuselage, and empennage. The operator reported that the engine had been overhauled (zero-timed) 31 hours before the accident. A postaccident engine examination revealed metal fragments and heavy gouging damage to the rotating components within the crankcase. The bottom portion (crankshaft end) of the n°1 linkrod and its respective bushing were missing from the n°1 linkpin; the oil sump contained metal debris consistent with heavily damaged remnants of these (and other) components. The n°2 cylinder barrel and linkrod and the n°3 linkrod showed deformation to the left (in the direction of engine rotation). Based on the damage observed in the engine, it is likely that the event that initiated the engine failure involved either the the n°1 linkrod bushing or the bottom portion of the n°1 linkrod; however, the extensive damage to these components precluded determination of the failure mode.

The pilot had been advised by the Federal Aviation Administration flight service station (FSS) specialist to remain clear of the destination airport until the specialist could issue a special visual flight rules clearance. Instrument meteorological conditions prevailed at the airport, with a strong southeasterly wind. About 8 minutes after initial contact, the FSS specialist attempted to contact the pilot to issue the clearance but received no response. A witness about 0.5 mile southeast of the accident site said he saw the accident airplane flying very low over the treetops. He said the weather conditions consisted of low clouds, rain, and gusty southeasterly wind estimated at 30 to 40 knots. He said that, as the airplane passed overhead, it turned sharply to the left. As he watched the airplane, the wings rocked violently from side to side, and the nose pitched up and down. As the airplane passed low over hilly, tree-covered terrain, it rolled to the right, the right wing struck a large tree and separated, and the airplane descended behind a stand of trees. Pilots flying in the accident area reported strong wind with significant downdrafts and turbulence. A postaccident examination of the airplane did not disclose any preimpact mechanical malfunctions. Given the lack of mechanical deficiencies and the reports of turbulence and downdrafts, as well as the witness’ account of the airplane’s physical movements, it is likely that the pilot encountered significant terrain-induced turbulence and downdrafts while flying at low altitude. The area surrounding the accident site and portions of the pilot's earlier flight path were bordered by large areas of open and protected water, several of which were suitable for landing the float-equipped airplane.

The single engine airplane was returning to its base in Ketchikan following maintenance in Thorne Bay. Shortly after takeoff, while climbing, the engine lost power, forcing the pilot to attempt an emergency landing. While landing on water, a control wire snapped, causing the airplane to nose down in the water, coming to rest upside down. All three occupants were rescued by coastguard 20 minutes later and the aircraft sank.