On July 21, 1985, a Lake LA-4 (registration N6668L) was involved in an aviation accident near Sidney, ME. Investigators recorded the probable cause as: The pilot's failure to maintain adequate clearance from a boat wake while operating at low altitude, which resulted in loss of control and subsequent collision with the water. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A seaplane encountered a boat wake while flying low, porpoised multiple times, and collided with the water nose-down at approximately 45 knots. The left pontoon detached during impact.
What happened
The pilot reported that the aircraft was maintaining step flight at an indicated airspeed of approximately 45 knots when it encountered a wake generated by a nearby boat. Following the encounter, the aircraft began to fly erratically and porpoised two or three times before colliding with the water surface. The impact occurred in an estimated nose-down attitude of 10 to 15 degrees, with engine power set to idle.
During the collision sequence, the left pontoon became detached from the airframe. The aircraft immediately began taking on water and sank approximately four minutes after the initial impact, according to pilot accounts.
Findings
Airspeed: Indicated 45 knots at time of incident
Attitude: Estimated 10 to 15 degrees nose-down upon water contact
Power Setting: Engine power was off during the event
Damage: Left pontoon detached; aircraft filled with water and sank
Contributing Factor: Encounter with a boat wake while flying low over water
Probable cause
The pilot's failure to maintain adequate clearance from a boat wake while operating at low altitude, which resulted in loss of control and subsequent collision with the water.