Incident Overview
On 6 May 2019, a Cessna 152 (registration SP-MAA) operated by Smart Aero Service was conducting a training flight at Mazowiecki Port Lotniczy Warszawa-Modlin (EPMO). The aircraft was occupied by a student pilot and an instructor pilot. During the approach to landing, the engine began operating unevenly, with uncommanded revolutions per minute (RPM) fluctuations between 1000 and 2000.
Sequence of Events
The pilot, noticing the irregular engine behavior, increased throttle to 2300 RPM and applied carburetor heat. The engine then resumed smooth operation. While on final approach to Runway 08, the pilot transmitted a MAYDAY call and was cleared to land as number one. The airport's operations duty officer declared a 'Full Emergency' alert, and the airport fire and rescue service (LSRG) positioned a vehicle in readiness.
The pilot executed the approach at elevated engine RPM. On short final, at a safe distance from the runway threshold, the pilot reduced power; the engine operated smoothly. The landing was normal. After landing, the taxi to the apron was uneventful, and LSRG intervention was not required.
Findings
During the post-flight inspection, a mechanic at the operator's facility found that the fuel primer lever had not been locked. An unlatched primer causes the engine to draw additional fuel beyond that set by the throttle, resulting in uneven operation. After locking the primer, the engine ran correctly across its entire RPM range during a ground test.
The investigation also reviewed airport emergency response. The tower controller did not transmit all required information to the operations duty officer for the full emergency declaration as per established procedures. Additionally, the tower controller did not switch to the emergency radio group, causing communication congestion. The existing procedures lacked a condensed action scheme for time-critical situations.
Actions Taken
The aircraft operator, Smart Aero Service, reminded pilots about the necessity of locking the fuel primer and the consequences of failing to do so. This briefing was conducted until all instructors and solo pilots were informed about correct primer use. Pilots were also reminded to memorize procedures for engine anomalies.
The airport management at EPMO planned to review emergency procedures with the Polish Air Navigation Services Agency (PAŻP), verify radio settings for the TETRA system's emergency group, and install an additional radio at the tower permanently tuned to the emergency group to facilitate immediate communication.