Incident Overview
While approaching the destination airport, the flight crew was unable to obtain a safe indication that the landing gear was extended. In response, the flight returned to the departure airport. Emergency procedures for gear extension were performed, but a safe gear indication was still not achieved.
Hydraulic Fluid Loss
The pilot determined that all hydraulic fluid had been lost. The aircraft was subsequently landed with the nose gear locked in the extended position and the main landing gear partially extended.
Post-Landing Examination
After landing, examination revealed that the right main gear hydraulic actuator had failed due to overstress along metal grain boundaries and at an area of low wall thickness. All hydraulic system pressures were found to be normal, and no other landing gear system failures were identified.
Mechanism of Failure
The actuator failure allowed all normal and emergency system hydraulic fluid to be lost through the failed actuator, leading to the inability to obtain a safe gear indication.