Accident Overview
On 17 September 2015, at 12:36 local time, a Cessna 152 (registration SP-KDL) operated by Targor Flight Club made a forced landing in a field near Szczepankowo, Poland. The aircraft, owned by a flight training organization, was conducting a cross-country training flight under visual flight rules in daytime visual meteorological conditions. The crew consisted of a 23-year-old instructor with a CPL(A) license and approximately 320 hours total flying time, and a 19-year-old student pilot with about 20 hours, training for a PPL(A). Neither occupant sustained injuries, and both evacuated the aircraft unassisted.
Sequence of Events
The flight departed from the Grądy airstrip (EPGY) at 11:27. While cruising at 150 meters above ground level near Łomża, the instructor initiated a simulated forced landing drill. The student selected a field and, after completing the simulation at about 100 meters altitude, advanced the throttle. The engine responded only to 1700–1800 rpm. The instructor took control and found that the throttle lever moved with abnormally low resistance and that lever movement produced no change in engine power. As the aircraft continued to lose altitude, the instructor prepared for an emergency landing. Due to the low altitude, suitable landing areas were limited. The aircraft touched down on a soft field, causing the nose gear to collapse and the aircraft to nose over. The aircraft sustained substantial damage.
Technical Findings
Post-accident inspection revealed that the bolt connecting the throttle control rod to the carburetor throttle arm was missing. The assembly consists of a bolt, washers, adjustment nuts, a castle nut, and a cotter pin. No parts of the connection were found in or near the wreckage. The engine itself was in a condition consistent with its time in service. A simulation on another Cessna 152 with a similar throttle return spring showed that when the linkage was disconnected, the throttle plate settled at a position yielding an engine speed of about 1500–1600 rpm on the ground. In flight, this would produce slightly higher rpm (1700–1800) due to reduced propeller load. This power was insufficient to maintain level flight. The return spring, installed according to the manufacturer's service manual, acted to open the throttle but not enough for continued flight.
Discussion
The investigation concluded that the most likely cause of the linkage separation was the loss of the retaining bolt, possibly due to the castle nut backing off after the cotter pin failed. Less likely, the bolt may have fractured from overtightening. The next scheduled 100-hour inspection was about 5 flight hours away; had the connection remained intact until then, the discrepancy might have been detected when engine cowlings were removed. The preflight inspection does not require checking this connection. The report notes that applicable airworthiness regulations (FAR 23.1143(g), CS-23.1143(g)) require that if a power control separates at the engine fuel metering device, the airplane must be capable of continued safe flight and landing. The installed spring did not achieve this, a condition also observed on another Cessna 152. Historical data from the NTSB (1964–1979) identified 148 throttle linkage separation events on single-engine aircraft, with recommendations issued in 1981 and 1986 to improve design and maintenance.