On September 15, 2023, about 1058 Pacific daylight time, an experimental, amateur-built Seawind 3000 amphibious airplane, N57TJ, was substantially damaged when it was involved in an accident near Bellevue, Washington. The pilot was fatally injured and the passenger was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

According to witnesses, the airplane was initially heard and then seen departing from Lake Sammamish in a south-southeast direction. During the step phase of takeoff, the airplane skipped on the water three times before pitching up, banking to one side, and then impacting the water. Several witnesses recalled the engine sounding normal.

Another witness, who was also a pilot of an amphibious airplane, saw the accident airplane during the takeoff and said everything looked normal. The airplane got up on the step and was close to takeoff speed when it hit three large wakes or waves. The first two waves led to significant bounces off the water that resulted in the airplane jumping up a few feet before coming back down and contacting the water again. However, when the airplane hit the third wave, it pitched up sharply and climbed about 30–40 ft before nosing down at a 30–35° angle, impacting the lake, and flipping over onto its back.

A security camera captured audio and video of the airplane during the accident sequence. The engine rpm increased shortly before the airplane came into view from the left side of the frame. The video was consistent with witness observations and showed calm water near the shoreline. Throughout the duration of the video, in the area where the skipping occurred, a lake swell slowly moved from left to right. A witness also reported that the lake swell was a result of boat activity near the south side of the lake.

The accident site was near the middle of the lake, and first responders described the area as having multiple floating airplane sections and the smell of fuel. They also reported that the canopy and sections of the forward fuselage were present, including the nose landing gear. The airplane wreckage was towed by local law enforcement on the day of the accident and was recovered from the water to a secure area the following day. The canopy, forward fuselage, and nose landing gear were not found during the recovery process.

Postaccident examination of the wreckage revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. The forward seat lap belts remained attached to the airframe structure and were unlatched and undamaged. The right forward seat shoulder harness was undamaged and remained attached to the right section of the canopy ceiling panel. The left forward shoulder harness inertia reel and webbing were not found during the examination. The shoulder harness canopy mounting bolt remained attached to the left section of the canopy ceiling.

During the initial response to the accident site, a diver reported that the pilot was only secured in his seat with the seat’s lap belt. Photographs from inside the airplane during previous flights revealed that on several occasions the pilot was not wearing a shoulder harness.

An Electronics International Inc. MVP-50P panel-mounted, electronic engine display was removed from the airplane and sent to the NTSB Vehicle Recorder Laboratory for download. The engine display recorded data for the entire accident flight, from 1053 to 1058. Although the recording contained about 11 seconds of invalid data for some parameters from 10:57:13.7 to 10:57:24.7, no other anomalies were noted in the data. Airspeed increased from 0 to 60 kts over the last 15 seconds of the recording.

The FAA Seaplane, Skiplane, and Float/Ski Equipped Helicopter Operations Handbook provided the following information on swell and skipping related to seaplane operations:

SWELL

Compared to operations from typical hard-surface runways, taking off from and landing on water presents several added variables for the pilot to consider. Waves and swell not only create a rough or uneven surface, they also move, and their movement must be considered in addition to the wind direction.

Even relatively small waves and swell can complicate seaplane operations. Takeoffs on rough water can subject the floats to hard pounding as they strike consecutive wave crests. Operating on the surface in rough conditions exposes the seaplane to forces that can potentially cause damage or, in some cases, overturn the seaplane. When a swell is not aligned with the wind, the pilot must weigh the dangers posed by the swell against limited crosswind capability, as well as pilot experience.

SKIPPING

Skipping can also occur by crossing a boat wake while taxiing on the step or during a takeoff. Sometimes the new seaplane pilot confuses a skip with a porpoise, but the pilot’s body sensations can quickly distinguish between the two. A skip gives the body vertical “G” forces, similar to bouncing a landplane. Porpoising is a rocking chair type forward and aft motion feeling.

To correct for skipping, first increase back pressure on the elevator control and add sufficient power to prevent the floats from contacting the water. Then establish the proper pitch attitude and reduce the power gradually to allow the seaplane to settle gently onto the water. Skipping oscillations do not tend to increase in amplitude, as in porpoising, but they do subject the floats and airframe to unnecessary pounding and can lead to porpoising.