Accident Overview
On February 25, 2020, at about 1220 Pacific standard time, an Ercoupe 415C, registration N3437H, was substantially damaged following a partial loss of engine power during takeoff near Torrance, California. The pilot and passenger were not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Flight Sequence
The pilot reported that after departure, she completed two touch-and-go practice takeoffs and landings. During the third takeoff, when the airplane had traveled about three-quarters of the length of runway 29R at an altitude of approximately 200 feet above ground level, the engine experienced a partial loss of power and began surging. The pilot executed a 90° left turn to land on a taxiway. After touchdown, the airplane veered left and collided with two parked airplanes.
Engine and Systems Examination
Postaccident examination revealed no evidence of a catastrophic engine failure. The magneto timing was found to be 2° and 4° retarded relative to the manufacturer's recommendation. Continuity of the fuel system was verified, and the engine was rotated with no anomalies detected.
Throttle Cable Findings
The throttle cable was secured at both ends: to the arm on the carburetor and to the throttle lever in the cockpit. However, movement of the throttle arm indicated that the throttle control in the cockpit did not initially retard correspondingly. Further inspection revealed that from the throttle arm, the rod was secured with an Adel clamp to the engine mount. Approximately 3/4-inch of movement of the arm produced movement of the rod that shifted the clamp and outer housing (sheath) of the cable, but the cable itself did not move (and thus did not move the throttle control) unless the arm was moved more than 3/4-inch. This was confirmed via borescope evaluation of the butterfly valve position in the throttle body. The forward and aft play in the throttle control caused the carburetor butterfly to deflect roughly 10° to 15° at full throttle and 20° to 25° at half throttle. Additionally, the rigging of the throttle cable from the panel to the throttle arm could have resulted in the rhythmic surging of the engine. If the throttle cable hits the stop at the carburetor end before the throttle knob reaches the panel, a bowing may occur in the cable. When bowed, the cable can act like a spring, failing to provide intended movement unless aligned.
STC Holder Input
The supplemental type certificate (STC) holder, Univair, was unable to determine where the throttle cable clamp, part number 415-40506, was designed to attach.
Similar Incidents
Several other recorded instances of similar circumstances in Ercoupe airplanes exist. For example, in NTSB investigation CHI08CA056 (Ercoupe 415D), the probable cause was a loose clamp on the throttle cable which prevented application of engine power. In investigation BFO94LA001 (Ercoupe 415E), the probable cause was failure of the airplane's throttle cable fitting due to undetermined reasons, preventing the pilot from applying power above idle. Additionally, NASA Aviation Safety Reporting System (ASRS) Report 698127 (Ercoupe 415C) described an engine surge during landing that led to a forced landing on a highway; post-accident examination revealed a loose bracket securing the throttle cable.