What happened
On February 12, 2017, during a pre-flight inspection at the HEMS (Helicopter Emergency Medical Service) unit in Warsaw, a professional helicopter pilot identified an issue with the aircraft's hydraulic system. The pilot observed that the hydraulic fluid level in the sight glass for hydraulic installation number 1 was too low. Additionally, traces of hydraulic fluid were found within the main gearbox compartment, specifically underneath the hydraulic control system actuators.
Following the discovery, the pilot recorded the findings in the aircraft technical log and notified the technical personnel at SOT Warszawa-Babice. The aircraft was immediately grounded to prevent further flight operations. Technical staff conducted an inspection and a pressure leak test in accordance with the Aircraft Maintenance Manual (AMM). The testing confirmed that hydraulic fluid was leaking from the control system actuators at a rate exceeding permissible limits.
The investigation
The investigation focused on the source of the fluid loss and the integrity of the hydraulic control components. Maintenance personnel performed a leak test following established procedures (AMM 67-31-00, 6-1). To rectify the issue, the longitudinal and lateral hydraulic control actuators were replaced as per the manufacturer's maintenance instructions (AMM 67-31-00, 4-3). After the replacement, the hydraulic system underwent further leak testing and a successful flight test, after which the EC 135 P2+ was returned to service.
Findings
- The primary cause of the hydraulic fluid leak was the operational wear of the seals within the longitudinal and lateral hydraulic control actuators.