Incident Overview

Date: Wednesday 1 November 2000
Aircraft Type: de Havilland Canada DHC-6 Twin Otter 100
Owner/operator: West Coast Air
Registration Number: C-GGAW
Location: Vancouver-Coal Harbour, BC – ÿ Canada
Phase of Flight: Initial climb
Status: Destroyed, written off
Casualties: Fatalities: 0 / Occupants: 17
Component Affected: The planetary gear.The planetary gear.
Investigating Agency: TSBTSB
Category: Accident
A West Coast Air Twin Otter floatplane experienced a catastrophic engine failure shortly after takeoff, resulting in a loss of control and separation of critical components. The failure of the second engine led to a rapid loss of propulsion and subsequent impact with the water.A West Coast Air Twin Otter floatplane experienced a catastrophic engine failure shortly after takeoff, resulting in a loss of control and separation of critical components. The failure of the second engine led to a rapid loss of propulsion and subsequent impact with the water.

Description

The West Coast Air Twin Otter floatplane departed Vancouver-Coal Harbour around 15:10 for a scheduled 35-minute flight to Victoria Harbour. Soon after takeoff, at a height of 50-100 feet, the no. 2 engine failed. The aircraft struck the water about 25ÿseconds later in a nose-down, right wing-low attitude. The right-hand float and wing both detached from the fuselage at impact. The occupants managed to clamber onto the aircraft’s pontoon and wing. Rescue boats, including a SeaBus passenger ferry, responded quickly to evacuate the passengers and crew from the plane. FINDINGS AS TO CAUSES AND CONTRIBUTING FACTORS: 1. A planetary gear disintegrated in the propeller reduction gearbox of the Noÿ2ÿengine and caused the engine drive shaft to disconnect from the propeller, resulting in a loss of propulsion from this engine. 2. The planetary gear oil strainer screen wires fractured by fatigue as a consequence of the installation at the last overhaul. This created an unsafe condition and it is most probable that the release of wire fragments and debris from this strainer screen subsequently initiated or contributed to distress of the planetary gear bearing sleeve and resulted in the disintegration of the planetary gear. 3. Although airspeed was above Vmc at the time of the power loss, the aircraft became progressively uncontrollable due to power on the remaining engine not being reduced to relieve the asymmetric thrust condition until impact was imminent.

Primary Cause

Disintegration of a planetary gear in the propeller reduction gearbox, causing a disconnect between the engine drive shaft and the propeller, resulting in loss of propulsion.Disintegration of a planetary gear in the propeller reduction gearbox, causing a disconnect between the engine drive shaft and the propeller, resulting in loss of propulsion.

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