Incident Description
During the initial climb after takeoff, the flightcrew experienced an uncommanded right rudder pedal hardover, during which the right rudder pedal moved to the fully depressed position. The crew deenergized the hydraulic system and subsequently made an uneventful landing at the departure airport.
Investigation Findings
A postincident examination of the airplane's rudder control system did not reveal any discrepancies. However, hydraulic system fluid samples were obtained and analyzed, along with an inspection, testing, and disassembly of the rudder hydraulic power control unit and the rudder actuators. The testing revealed contamination in the fluid samples from the airplane's hydraulic reservoirs and the power control unit that exceeded the maximum levels established by the airplane manufacturer's maintenance manual.
Operator Procedures
The operator's FAA accepted general operating manual requires compliance with the manufacturer's maintenance manual. Additionally, the operator did not have an established procedure for periodically sampling and analyzing hydraulic fluid from airplane systems.