Accident
On a no-search-and-rescue flight, a floatplane registered as VH-BSL departed Bundaberg, Queensland, at 1135 hours Eastern Standard Time for Monduran Dam. The aircraft carried three persons: the pilot in command, a pilot under check, and a passenger who was the regular pilot of the aircraft. The flight had an endurance of 270 minutes. Its purpose was to complete the endorsement of the pilot under check and to assess a coastal water area for a planned flight the following day.
The pilot in command had logged 27 flight hours in the previous three months, of which 9 were on the accident aircraft type. The pilot under check had flown only one hour in the preceding three months, all of which was in VH-BSL.
At approximately 1200 hours, the aircraft was observed near Lake Monduran. It performed two left-hand circuits, landing into the wind toward the dam wall on each occasion. After the second takeoff, the aircraft turned left and headed north from the lake. No further communication or sightings occurred.
Wreckage Location and Condition
An extensive search was conducted. Six days later, the wreckage was located inverted in 15 meters of water, approximately 2 kilometers west-northwest of the dam wall, at the junction of the main east-west channel and a north-south channel of the lake. Both floats had separated from the aircraft. The right float was severely torn for about half its length. The aircraft sustained substantial water impact damage to the windshield frame, cockpit roof area, and the upper leading edge surfaces of both wings.
Investigation
The official investigation found no fault with the aircraft or its systems that might have contributed to the accident. It could not be determined who was manipulating the controls at the time of the accident. Evidence indicated that the check pilot had a habit of having pilots under check or endorsement fly two circuits landing into wind, followed by crosswind landings. Both the check pilot and the pilot under check had previously operated at the dam and alighted on both the east-west and north-south channels.
After being observed flying two into-wind circuits and then heading north, it is possible that the aircraft commenced crosswind operations onto the north-south arm of the lake, landing in a southerly direction with a crosswind from the left. The Bureau of Meteorology reported that the surface wind at the time was 090 degrees magnetic at 15 knots. Witnesses at the dam wall confirmed the wind conditions, noting white caps on the water surface.
The north-south channel is bounded on its east side by steep hills rising to 70 meters above water level. This high ground partially blanketed the channel from the easterly wind. The wreckage position was in an area where the wind shadow effect would have ended and the wind would have blown at full strength along the east-west channel.
The crosswind limitation for the aircraft, as stated in the flight manual, was 8.7 knots. The aircraft manufacturer had emphasized this limit in a 1988 comment and advised caution for any test work to raise it. If the aircraft was conducting crosswind operations in the north-south channel and suddenly encountered a 15-knot crosswind upon exiting the wind shadow area, the control difficulties confronting the pilot could have been significant.
Damage Analysis
The aircraft wreckage was intact except for the floats, which had been torn off by water impact forces. The right float was severely damaged, while the left float was intact. The forward tip of the right float had been severed by the propeller. The remaining forward section was forced upward and outboard, breaking off. This weakened the float support structure, causing it to fail and allowing the remaining section of the right float to strike the right side of the fuselage just aft of the cabin. Such damage most probably resulted from the nose of the right float digging into the lake surface at relatively high speed. For this to occur, the aircraft was banked to the right at float impact—a possible consequence of encountering a strong crosswind from the left. There was no evidence that the aircraft struck a submerged object.
The factors associated with the development of this accident could not be determined.