Accident Overview
On May 7, 2019, about 1600 Pacific daylight time, a Flight Design CTLS, registration N423EB, was substantially damaged when it struck a municipal pond after a go-around at Boulder City Municipal Airport (BVU), Boulder City, Nevada. The pilot sustained serious injuries, and the passenger received minor injuries. The flight was conducted as a personal flight under Title 14 Code of Federal Regulations Part 91.
Flight Sequence
The flight departed with the purpose of a scenic tour over a nearby lake. After reaching the lake at a cruise altitude of 4,000 ft mean sea level (msl), the pilot reported a spontaneous increase in engine rpm and indicated airspeed to 134 knots from a previous setting of 5,000 rpm and 95 knots with autopilot engaged. The pilot retarded the throttle to idle, observing no change in rpm for about 8 seconds until it reached idle. He then re-advanced the throttle to 5,000 rpm and saw a warning message "Rotax: Land airplane" and an illuminated "ECU Channel B" warning light.
Returning to BVU, about 5 nautical miles (nm) from the airport, the pilot descended to 3,000 ft msl with throttle idle but could not slow to 80 knots to deploy flaps. Unable to descend with appropriate nose attitude, he performed the emergency descent checklist from the pilot's operating handbook (POH) by reducing throttle to idle and initiating a slip. The airplane crossed the runway at about 100 ft above ground level (agl) with excessive speed. The pilot aborted the landing and attempted a go-around by advancing throttle to full power. Seconds later, while crossing the departure end of the runway, the pilot noticed a high rate of descent, turned left about 10°, and heard three beeps indicating high angle of attack before impact.
Witness Account
A witness located about halfway down the runway observed the airplane approach excessively fast and high for its position. It floated over the runway near the 1,000 ft marker for about 1,700 feet. The airplane then initiated a go-around but the engine did not initially sound at full power. After reaching about 200 ft agl near the end of runway 15, the airplane entered a nose-high attitude followed by a nose-down dive in a slight left turn, impacting terrain beyond airport property.
Data Recovery
Engine and airplane performance data were recovered from two Dynon Skyview primary flight displays (PFD) and fault warning data from an engine control unit (ECU). The Dynon data showed throttle position increased from 83 to 88 between 1549:33 and 1549:36, with rpm rising from 4,450 to 4,900 and true airspeed (TAS) from 98 to 122 knots. The data indicated the engine responded to commanded throttle positions throughout the flight with no anomalies. The ECU recorded two faults: one about 7 minutes before the end of data correlating to the Lane B failure near the lake, reading "Nominal Current Not Reached" (which the manufacturer stated would not affect power), and another at engine shutdown.
Later descent data showed the airplane's maximum TAS of 134 knots (124 KIAS) at 1555:06. On short final, vertical speed increased momentarily. During the landing attempt, airspeed reduced from about 76 to 53 knots over the first half of the runway, with engine power at 1,600 rpm. Over the last half, engine rpm advanced to 4,695 rpm (95% throttle) while airspeed decreased to 47 knots. At the runway end, pitch attitude reached 14° nose-up and airspeed dropped to 35 knots before impact. According to the POH, stall speed with no flaps was 47 knots indicated.
Post-accident Examination
Post-accident examination of the airframe confirmed flight control continuity from cockpit to primary control surfaces. Throttle control continuity was verified from the throttle lever to the throttle body, displaying full travel. The fuel system was intact. Mechanical continuity from the accessory case to the propeller was confirmed; thumb compression and suction were present on all four cylinders, though valvetrain movement was only partially verified due to propeller seizure. Cylinder No. 4 exhibited lead deposits reducing clearance. All three Neuform composite propeller blades were damaged: one fractured at the root, one at the tip, and one cracked at midspan.
Engine performance calculations based on density altitude of 1,389 m indicated a maximum of about 85 hp (64 kW) and 5,300 rpm. However, the aircraft manufacturer's propeller pitch limited maximum static rpm to 4,950 and climb rpm to 5,100, resulting in an estimated climb rpm of 4,600 on the accident day.