What happened
On October 30, 2009, a Cessna 172RG, registration OK-ALZ, was performing a solo navigation flight as part of a pilot training program. The flight originated from Roudnice and was scheduled to land at Panensk and Týnec Airport.
During the landing approach on runway 09, the pilot extended the landing gear and performed a visual check of the left main gear. The pilot reported seeing a green indicator light, signifying the gear was down. However, upon touchdown, the aircraft exhibited unusual behavior, characterized by a sudden sinking and a veer to one side. The pilot attempted to initiate a go-around, but due to the low airspeed, the maneuver was unsuccessful. The aircraft subsequently exited the runway onto the grass. There were no injuries to the pilot, though the aircraft sustained damage to the rear fuselage and tail surfaces.
The investigation
An investigation by the ÚZPLN focused on the mechanical state of the landing gear and the pilot's actions. Investigators examined the hydraulic system and the electrical components of the gear deployment mechanism. Upon inspection of the cockpit after the accident, the "GEAR PUMP" circuit breaker was found in the tripped position.
Technical testing of the aircraft's landing gear system, including dozens of extension and retraction cycles under simulated low-voltage and low-fluid conditions, revealed no mechanical obstructions or hydraulic leaks. The investigation also analyzed a video recording of the landing, which allowed investigators to determine the touchdown point and observe the shadow of the landing gear, confirming the gear was not fully extended.
Findings
- The extension cycle of the landing gear was interrupted because the "GEAR PUMP" circuit breaker tripped, likely due to a current surge in the hydraulic pump motor when the gear lever was moved to the down position.
- While the nose gear successfully extended and locked, the main landing gear failed to complete its extension and locking cycle.
- The pilot's belief that the green indicator light was illuminated was incorrect; the investigation determined the light could not have been lit because the sensors for the main gear had not yet reached the locked position.
- The pilot, a student undergoing PPL(A) training, had not performed a functional check of the indicator lights prior to flight.
- The pilot's recent experience with retractable gear was limited, having only performed a few flights on this specific type recently.