De Havilland BEAVER DHC 2 N4787C

Summary

On 24 July 2013 at about 19:40 local time, a De Havilland BEAVER DHC 2 registered N4787C, operated by Promech Air LLC, was involved in an accident near Thorne Bay, Alaska, United States. 4 people were on board and 3 were seriously injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

24 July 2013 at 19:40

Classification

Accident

Location

Thorne Bay, Alaska, United States

Coordinates

55.8250, -132.8850

Aircraft

De Havilland BEAVER DHC 2

Registration

N4787C

Category

Airplane

Engines

1

Operator

Promech Air LLC

Operating rule

Part 135: Air Taxi & Commuter

Phase of flight

Not recorded

Route

Ketchikan → Shipley Bay

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

ANC13LA068

3 people were seriously injured.

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

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

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.

Quoted verbatim from the NTSB record.