Incident Overview
Following departure, the pilot selected the landing gear to the retracted position but did not receive a gear up indication. Another aircraft flew underneath and observed that the nose gear and left main gear were fully retracted, while the right main gear was only partially extended. Attempts to correct the asymmetric gear condition were unsuccessful, and the aircraft was subsequently landed with the landing gear in that configuration.
Post-Crash Findings
A post-crash inspection of the aircraft revealed that a secondary relief valve in the hydraulic power pack was being held open by contamination. This allowed hydraulic pressure to bypass the landing gear actuators, preventing the right main gear from fully retracting or extending properly.
Maintenance History
Examination of the aircraft's logbook records showed no evidence that the hydraulic power pack had ever been overhauled. Additionally, there was no indication that a modification to remove the secondary relief valve had been complied with.