What happened
On April 20, 2017, a Reims Aviation F177RG, registration HB-CGM, was conducting a training flight for license renewal at Birrfeld Regional Airport (LSZF). During the approach phase, the pilot attempted to extend the landing gear but noticed the green indicator light failed to illuminate. Visual inspection via a wing mirror revealed that the main landing gear was only partially extended.
The crew attempted emergency procedures outlined in the Aircraft Flight Manual (AFM), including the use of the manual hand pump. However, the pump lever moved without resistance, suggesting a total loss of hydraulic pressure. After various maneuvers and attempts to manually pull the gear, the crew utilized an unconventional method to secure the gear. Using a jumper cable found in the baggage compartment, the pilot managed to loop the cable around the right landing gear leg. While the instructor maintained a slow glide with landing flaps extended, the pilot used the cable to pull the gear into the locked position. The left gear was also manually secured, allowing for a safe landing on runway 08.
The investigation
SUST examined the hydraulic extension and retraction mechanism of the aircraft to identify the source of the pressure loss. The investigation focused on the hydraulic lines servicing the gear assembly.
Findings
Technical analysis revealed a leak in a hydraulic line leading to the nose gear cylinder. Specifically, a crack was discovered on the inner surface of a curved aluminum tube. The investigation found that the tube's cross-section had become oval rather than circular, and the metal exhibited sharp dents and irregularities. These findings indicate that the aluminum tube had been improperly bent, likely using unsuitable tools or excessive manual force. This improper bending caused plastic deformation, which ultimately led to the formation of the crack and the subsequent loss of hydraulic fluid.