Dehavilland BEAVER DHC 2 N4787C accident near Thorne Bay, Alaska

Probable cause

The failure of the No. 1 linkrod bushing or the bottom portion of the linkrod, which resulted in a total loss of engine power.

NTSB analysis

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 No. 1 linkrod and its respective bushing were missing from the No. 1 linkpin; the oil sump contained metal debris consistent with heavily damaged remnants of these (and other) components. The No. 2 cylinder barrel and linkrod and the No. 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 No. 1 linkrod bushing or the bottom portion of the No. 1 linkrod; however, the extensive damage to these components precluded determination of the failure mode.

Text from the NTSB. Open the NTSB docket for ANC13LA068 for the full record.