What happened
During a takeoff attempt from a lake, an airline transport pilot was operating a float-equipped airplane carrying a load of passengers. The pilot had previously flown this group to the location earlier in the day. Before the departure, the pilot calculated the required water run to be 1,050 feet and the distance needed to clear a 50-foot obstacle to be 2,210 feet. However, these calculations did not include a safety margin. The available distance from shore to shore for the takeoff path was approximately 1,800 feet.
During the taxi phase, the pilot left the wing flaps in the retracted position. GPS records indicate that the aircraft reached a speed of roughly 49 knots before it struck the ground just past the shoreline. At this speed, the aircraft was flying below its stall speed, which was approximately 5 2 knots for the configuration used. Post-accident inspections confirmed that the left flap was fully retracted and the right flap assembly sustained damage.
Findings
Investigation into the accident revealed that the pilot failed to follow the airplane flight manual takeoff checklist, which required flaps to be set to the "TAKE-OFF" position. The performance data provided in the manual was specifically based on using the correct takeoff flap setting and did not provide parameters for takeoff without flaps.
The pilot's failure to use the required takeoff flaps contributed to the loss of lift and performance. However, even if the correct flap setting had been utilized, the calculated takeoff distance required to clear obstacles was nearly equal to the available distance, suggesting a collision with the terrain might have been unavoidable. The pilot noted that no mechanical failures occurred and acknowledged that the load should have been split into two separate flights to ensure safety.