Accident Details
On April 14, 2004, a de Havilland DHC-6-300 amphibious aircraft, registration C-GOGC and serial number 750, was conducting firefighting operations near Lake Wicksteed, approximately 10 nautical miles north of Hornepayne, Ontario. The single pilot on board was performing the third water scooping from the lake, which is about 7,300 feet long with gentle rising terrain along its shoreline. The approach was flown in an easterly direction under light wind conditions. After lowering the water probes and touching down, the pilot observed water spraying from overflow vents on top of the floats, indicating the tanks were full. He pressed a button on the yoke to retract the probes, and the aircraft immediately nosed over into the lake in a wings-level attitude and began to sink. The accident occurred at approximately 1800 Eastern Daylight Time.
Rescue and Aircraft Condition
The pilot extricated himself and held onto the side of the partially submerged aircraft. A witness immediately went to assist in a powered aluminum boat, while another witness traveled to Hornepayne to notify authorities. The pilot reached the shore and was taken to a nearby cottage until emergency services arrived. The aircraft came to rest on the bottom of the shallow lake in an inverted attitude with the floats above the water surface.
Aircraft and System Description
The Ministry of Natural Resources (MNR) operates five de Havilland DHC-6 Twin Otters for firefighting, equipped with amphibious Wipline 13000 floats modified with water holding tanks and probes. The probes, located on the bottom of the floats, extend to fill the water tanks. Water bomb doors, two on each float bottom, and the probes are electro-hydraulically operated and share hydraulic pressure with the aircraft's system. They are controlled by two push-button switches side-by-side on the left yoke. The bomb door push-button switch is covered by a hinged plate that must be raised to expose the button. A door armed switch on the center panel must be selected ON for the system to be active. Position indication is provided by six green lights on the center panel (doors retracted, probes stowed, door jacks retracted); an amber light indicates the door armed switch is ON; a separate amber light illuminates if doors or probes are extended; a red light and horn activate if bomb doors open without being selected. A dump lever allows emergency water ejection via free-fall, and a hydraulic hand pump retracts doors if the electric pump fails.
Contributing Factors
MNR Standard Operating Procedures (SOPs) were not followed, and the Vital Action checklist was not fully completed during the approach. Consequently, the bomb door armed switch on the center panel was not selected OFF after the previous water bombing run and prior to the scooping operation. After completing the water scooping, the pilot unintentionally selected the bomb door push-button switch instead of the adjacent probe switch. Because the bomb door armed switch was left ON, the bomb doors extended into the water. Drag from the doors and water rushing into the door openings caused the aircraft to nose over. Additionally, the hinged cover plate for the bomb door push-button switch had not been reinstalled following maintenance to replace the switch, leaving the push button exposed and making inadvertent selection more likely. The MNR verified that every Twin Otter in their fleet is equipped with the cover plate and will ensure future modifications are standardized to decrease the potential for inadvertent operation.
Investigation Conclusion
This report concludes the Transportation Safety Board's investigation into this occurrence. The Board authorized the release of this report on April 14, 2004.