What happened
On January 8, 2001, a Cessna 177-RG, registration EC-GCX, was performing a non-commercial VFR flight from Madrid/Cuatro Vientos to Casarrubios del Monte. Shortly after takeoff, the pilot attempted to retract the landing gear but noticed the gear-up indicators failed to illuminate.
After communicating the issue to the control tower, the pilot attempted to extend the gear using standard procedures and the manual emergency procedure, but the gear failed to lock in the down position. While performing a low-altitude pass at the destination aerodrome to visually check the gear position, the engine stopped, forcing an emergency landing. During the touchdown, the landing gear collapsed, causing the propeller and the lower fuselage to strike the pavement and slide along the runway. The pilot was uninjured, though the aircraft sustained damage to the landing gear, propeller, engine area, and fuselage.
The investigation
Post-accident inspections of the aircraft revealed that the hydraulic system was completely empty due to a leak. Upon refilling the system in the workshop, investigators identified a crack in a metal pipe segment connecting to the hydraulic pump. While the pilot had attempted to use the manual emergency pump to pressurize the system, this was ineffective because the fluid escaped through the existing crack.
Metallurgical analysis of the failed pipe, conducted by the National Institute for Aerospace Technology (INTA), showed that the component lacked protective anti-corrosive coating. The study found evidence of intergranular corrosion, which acted as the starting point for fatigue cracks. These cracks were further propagated by static stresses from the pipe's installation and operational vibrations.
Findings
- The primary cause of the hydraulic failure was a rupture of the hydraulic line caused by intergranular corrosion and subsequent fatigue cracking.
- The corrosion was likely triggered by exposure to corrosive vapors or liquid spills from the aircraft battery, which is located directly above the pipe segment.
- Contributing factors included permanent mechanical stress from the pipe's installation and continuous operational vibrations.
- The emergency landing gear procedure was unable to compensate for the leak because the system could not maintain pressure.