WPR21LA011

The pilot and pilot-rated passenger were departing from a grass runway. The passenger stated that the airplane remained in ground effect for a large duration of the takeoff and then climbed above the treeline. At an altitude of about 75 ft above ground level, the airplane’s left wing stalled, and the airplane collided with terrain. Analysis of video of the accident takeoff and GPS data indicated that the airplane’s wing reached its critical angle of attack before it began to lose altitude and descend into terrain. Sound spectrum analysis of the engine indicated that it was producing power at the time of the accident. Given the weights of the pilot, passenger, and fuel onboard, the airplane was under its maximum gross weight and within its center-of-gravity limits at the time of the accident. The circumstances of the accident are consistent with the pilot’s exceedance of the airplane’s critical angle of attack during the initial climb, which resulted in an aerodynamic stall and loss of control.

The experimental, light-sport, high-wing amphibious airplane was manufactured in 2008. It was equipped with a 100-horsepower Rotax 912-S engine which drove a three-bladed composite propeller manufactured by Warp Drive. The basic empty weight was recorded as 732 lbs and with a maximum gross weight of 1,320 lbs. A Ran’s Pilot Operating Handbook (POH) was not available for the amphibious configuration. The Ran’s POH for a tailwheel configuration airplane indicated that normal takeoffs are accomplished with flaps up or half extended. With the flaps retracted, the normal climb speed was 65 to 70 mph. The POH further stated that, with the flaps half extended during takeoff, they should be left in that position until all obstacles were cleared, airspeed exceeds 60 mph, and the airplane gains a minimum altitude of 100 ft above ground level (agl) is reached. The POH stated that the stall speed at maximum gross weight in a flaps-retracted position was 50 mph. Stall speed for flaps at half retracted was 48 mph. The stall recovery procedure advised the pilot to smoothly move the control stick forward to accelerate to normal flight speed. The passenger estimated that the airplane contained about 11.25 gallons of fuel at the time of departure. According to Rans Aircraft, the accident airplane would have been under gross weight and well within the center-of-gravity envelope. On October 06, 2020, at 1533 Pacific daylight time, a Rans S-7 Courier amphibious airplane, N55893, was substantially damaged when it was involved in an accident near Spirit Lake, Idaho. The pilot sustained fatal injuries and the passenger sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot and pilot-rated passenger were departing from the 3,000-ft-long grass runway. During the initial takeoff, the airplane stayed in ground effect. The passenger thought the pilot was going to land and taxi back, but then the pilot pulled aft on the control stick. The airplane climbed above the trees at the end of the runway (about 40 ft tall) and at about 50 ft above ground level (agl), the airplane’s left wing stalled. The airplane impacted the ground nearly inverted. A review of video of the takeoff revealed that the airplane became airborne about 1,100 ft down the runway. (see figure 1.) As the departure continued, the airplane’s wings rocked as it slowly climbed above the tree line. (see figure 2.) The airplane turned left (to the north) and then descended below the tree line. The airplane came to rest about 900 ft north of the runway centerline. (see figure 3.) Figure 1: Runway Diagram Figure 2: Excerpts of Video Capturing Takeoff Figure 3: Accident Site in Reference to the Runway In an effort to determine the estimated ground track, ground speed, altitude, orientation angles and engine speed of the airplane, the NTSB completed a performance study using the video of the accident takeoff as well as data recorded by an onboardmulti-functional display (MFD) and GPS receiver. The track data indicated that, after becoming airborne, the airplane’s groundspeed increased from 47 to 60 mph, then decreased to 58 mph as the airplane climbed over the treeline. The video revealed that, after departing the runway surface and about 22 seconds after becoming airborne, the airplane reached a maximum altitude of about 75 ft above the runway, and subsequently began descending. The angle of attack (AOA) of the wing was derived from the video footage evaluating the difference between the wing pitch angle and the flight path angle (because wind was reported as calm, wind was not factored into the calculations). The wing stalled about 15 seconds after becoming airborne, resulting in the large 19° roll angle change between 13.67 and 18 seconds. At 25 seconds, the estimated angle of attack was 20°, which exceeded the wing’s critical AOA. The airplane impacted the ground about 650 ft from the last data point. The sound spectrum analysis of the video revealed that the estimated engine speed was about 5,446 rpm, equating to about 94% of the rated engine speed of 5,800 rpm. The engine and the propeller were operating about that speed when the airplane was losing altitude, consistent with normal engine operation. Utilizing a temperature of 27 degrees Celsius and the airport elevation, the density altitude at the time of the accident was computed to be approximately 4,453 feet msl. The pilot’s personal flight records were not recovered. On his most recent application for a Federal Aviation Administration medical certificate in October 2019, the pilot reported a total flight time of 10,000 hours. He purchased the airplane on May 7, 2000.