There were five persons on board the Cessna 185 floatplane when the pilot taxied for a charter flight from the wharf at Strahan, Tas. The pilot steered the aircraft out of the cove into more open water to position the aircraft for takeoff into the prevailing northerly wind.
The pilot reported that the aircraft had travelled approximately 1 km, and was at the start of the planned takeoff run, when he assessed the water state as being marginal for the aircraft. He then began steering the floatplane back towards the wharf when a catamaran cruise boat, travelling in the opposite direction, passed on the left. Waves generated by the accelerating catamaran prompted the pilot to steer the floatplane left to cross the bow-wave head on. After negotiating the wake the pilot resumed course to the wharf. The pilot then became concerned about the buoyancy of the right float and broadcast his concerns. He increased power and applied left aileron and aft elevator to counter the increasing list to the right but the aircraft nosed over and came to rest inverted.
The pilot and two passengers were able to evacuate quickly from the submerged cabin and were followed a short time later by another passenger. At that time, the pilot was diving to assist the remaining passenger, who eventually surfaced unaided. Three life jackets floating in the water nearby were retrieved by the pilot and were donned by passengers. The pilot and passengers were rescued a short time later by a nearby boat and another floatplane.
The pilot had been tasked to use a floatplane that was positioned in a hangar near the water. While the preflight inspection in the hangar had revealed only a small amount of water in the two float lockers, the pilot intended to pump out the other six float compartments on each float when the floatplane was tied up at the wharf. He was aware that the floats had been prone to taking on water and that pumping out the floats prior to his previous flights in the aircraft had removed substantial amounts of water. It was also standard operating procedure for the operator's pilots to pump out the float compartments as part of their daily preflight inspection. However, the floats were not pumped out, and the aircraft departed the wharf with an unknown amount of water in the floats.
While the pilot could recall being subject to time pressure after the aircraft was positioned at the wharf, he was not able to clearly remember the specific circumstances that contributed to the situation. The pilot reported that he had arrived at work at 0815 Eastern Standard Summer Time and started his duty period at 0830 for a planned 0900 departure.
The pilot stated that, soon after departure from the wharf, the aircraft `felt odd'. He then radioed a colleague located in the wharf office, who indicated that the right wing was slightly low. At the time the pilot attributed the aircraft attitude to fuel imbalance, passenger loading and the wind effect. Before entering the more open water, the pilot had momentarily turned the aircraft into wind and was satisfied with the level of the wings and water handling. While the pilot attempted to observe the performance of the right float a number of times, he found it difficult to see the float from the left side of the aircraft. During the outbound taxi, the front passenger had advised the pilot that the right float was low in the water and had water breaking over it. The pilot reported that he only became concerned about the ability of the floatplane to stay afloat after the encounter with the wake of the cruise boat. At that stage he considered that beaching the floatplane was impractical due to the unsuitability of the adjacent coastline.
The front passenger later stated that the right float was basically submerged by the time the wake from the catamaran had been negotiated. He also stated that there were two round holes of approximately 30 mm diameter on the top of the right float that allowed water to enter the float. This was likely to have been the access holes for the smaller diameter bilge tubes. The access holes are normally sealed with a removable bung. The pilot stated that one or two bilge tubes were missing from their holes in the right float. Following discussions with the pilot and other company personnel, the investigation was unable to determine the point in time when the right float bungs became separated from the floats.
The passengers stated that the operator's personnel had briefed them on life jacket use when they were checked-in for the flight. The pilot had also given the passengers a pre-departure briefing that included the location of the life jackets. A life jacket was stowed under each of the seats.
Civil Aviation Order (CAO) Section 20.11, Parts 5.1.4 and 5.1.5 describe the requirements for the equipping of floatplanes with life jackets. Part 5.1.8 describes the requirements for the wearing of those life jackets and states, in part: `However, occupants need not wear life jackets when the aircraft is taking-off or landing at a aerodrome in accordance with a normal navigational procedure for departing from or arriving at that aerodrome, and occupants of aeroplanes need not wear life jackets during flight above 2000 feet above the water.' Aerodrome is defined in Aeronautical Information Publication Australia, Amendment 33, as `A defined area of land or water (including any buildings, installations and equipment) intended to be used either wholly or in part for the arrival, departure and movement of aircraft.'
