What happened
On 23 May 2022, a Tecnam P2006T, registration SP-MMB, was conducting a training flight from the Warsaw-Babice aerodrome (EPBC) with a crew consisting of a flight instructor and a student-pilot. The flight proceeded normally until the crew attempted to extend the landing gear upon returning to the aerodrome.
Despite multiple attempts to move the landing gear lever to the down position, the extension signal failed to appear. The crew subsequently performed the emergency checklist for landing gear system failures. However, the alternate landing gear extension system also failed to function. After a low pass to confirm the gear status with ground personnel, the crew performed a landing on a grass runway with the gear retracted. The impact caused damage to the lower fuselage skin and the main landing gear nacelles.
The investigation
The PKBWL investigation examined the electrical and hydraulic components of the landing gear system. Investigators utilized computer tomography to perform non-invasive tests on the faulty relays. The analysis revealed that under certain flight conditions, aerodynamic and inertial forces can increase the current consumption of the hydraulic pump motor beyond the rated capacity of the installed electrical relays.
Furthermore, the investigation looked into the mechanical connection of the alternate extension valves. It was discovered that the lever on the shaft of the first discharge valve was not sufficiently secured, allowing it to loosen and rotate freely, which prevented the valve from opening correctly.
Findings
- The primary cause of the incident was the use of inappropriate components by the manufacturer within the landing gear extension and retraction system, specifically relays that were prone to fused contacts when subjected to high current loads.
- A contributing factor was the presence of errors in the execution of the alternate landing gear extension procedure.
- The investigation also identified the insufficient securing of the lever mounted on the shaft of the first discharge valve, which allowed for spontaneous loosening.
Safety action
The PKBWL issued several safety recommendations to the aircraft manufacturer, including:
- Analyzing and replacing all system components whose load exceeds their rated current values.
- Modifying the emergency checklist to include the instruction to pull the "LANDING GEAR" circuit breaker to depressurize the system, and marking said breaker with a bright color for visibility.
- Redesigning the connection between the first discharge valve lever and its shaft to prevent spontaneous loosening.
- Issuing a service letter or bulletin to inform operators of these issues and provide temporary solutions until permanent modifications are implemented.