What happened
On January 13, 2020, a Tecnam P2006T, registration SP-KEY, was conducting a training flight near Bydgoszcz (EPBY) as part of an instrument rating program. The flight was operating in clouds with an external temperature of +2°C and moderate humidity, conditions favorable for icing. During the initial climb, the instructor activated the carburetor heat to prevent icing.
While performing a visual approach to runway 26, the crew initiated a go-around procedure at approximately 350 feet AMSL. During the climb, the right engine began to malfunction, exhibiting power loss and audible knocking consistent with detonation. The instructor took control, performed a 180-degree turn, and transitioned to level flight. After reporting the engine issue to the tower, the instructor shut down the right engine. However, the fuel valve remained closed, which prevented the engine from being restarted when the left engine subsequently began to malfunction with similar symptoms.
The crew performed an emergency landing on the grass near the threshold of the runway. Subsequent inspections by a mechanic and a follow-up test flight revealed that both engines were functioning correctly.
The investigation
The PKBWL examined the use of carburetor heat during the flight. While the crew correctly used the heat during the climb due to icing conditions, they failed to switch the heat to the "OFF" position during the final checks of the go-around. The investigation also reviewed the manufacturer's Service Information Letter (SIL-2017-02), which advises that carburetor heat should be minimized to avoid engine damage from detonation, specifically recommending against its use when engines are operating above 75% power or when icing is not a threat.
Findings
- The primary cause of the incident was operating the engines at full power with the carburetor heat engaged during the go-around procedure, which caused the fuel to boil in the carburetors and led to detonation.
- The crew was unaware of the specific instructions contained in the manufacturer's Service Information Letter regarding the risks of detonation.
- The right engine could not be restarted because the fuel valve was left in the closed position.
Safety action
- Pilots operating Tecnam P2006T aircraft should be briefed on the circumstances and causes of this incident.
- Pilots must be made aware of the correct procedures for using carburetor heat during various flight phases and meteorological conditions, as outlined in both the Pilot's Operating Handbook and Service Information Letter SIL-2017-02.