This month’s maiden flight of the Comac C919, the largest commercial airliner designed and built in China since the defunct Y-10, marks a major milestone in China’s long-term goal to compete with Boeing, Airbus and Bombardier.
But the C919 has relied on extensive Western input for its design and manufacturing. Nowhere is this more the case than in the new aircraft’s hydraulic systems. For example, Parker Aerospace, part of Parker Hannifin, provides all of the key fluid power systems on the new C919. In fact, the Parker Aerospace Hydraulic Systems Division provided the complete hydraulic system, including engine-driven hydraulic pumps, AC motor pumps, power-transfer units, reservoirs, filter modules, accumulators and ground service panels.
These components are installed in three independent hydraulic systems on the C919 and provide fluid power for flight-control actuation, landing-gear retraction and extension, nose-wheel steering and thrust-reverser deployment. The system as a whole is very much East meeting West: some of the mechanical components are provided by Parker’s joint-venture partner on the C919, the Avic Nanjing Engineering Institute of Aircraft Systems, and its supplier, Avic eXinhang.
Today, linear hydraulic actuators play an indispensable role within aircraft systems. “Thanks to the high power-to-weight ratio of hydraulic components and high reliability, hydraulic power has been used for landing-gear, flight-control and other utility actuation, such as nose-wheel steering and door actuation,” says Steve Devan, engineering manager of hydraulic pumps and motors for the aerospace group, at power management giant Eaton, which has been manufacturing hydraulic components since the first Boeing and Airbus platforms went into production.
Eaton now provides repair services for fuel, hydraulic and actuation components. Repair capabilities include minor repairs, overhauls and upgrades in addition to customized support and service agreements, such as power-by-the-hour programs.
While Eaton supplies and repairs hydraulic systems and components, operators are responsible for system repairs. Most system issues involve leakage resulting from tubing damage, such as chaffing or dents, which can be repaired using Eaton Rynglok fittings. Eaton provides all of the necessary tools and fittings to OEMs, MROs and operators to repair damaged tubing.
Issues also can emerge from normal wear of component dynamic surfaces, such as pump shaft seals. Eaton can service those components and complete full overhauls with warranties—similar to installing new components, the company says.
Eaton’s zonal powerpack offers a localized, fully self-contained hydraulic system to power the third channel of critical flight-control actuators.
Richard May, managing director at UK MRO Aerotek Aviation Engineering, has extensive experience in managing a team that delivers MRO for hydraulic systems in older aircraft. Aerotek works on the hydraulics and landing gear of the BAE Systems Hawk, Sepecat Jaguar, Shorts SD3-60 and BAe 146, as well as the Airbus A321 and Boeing 737. “Most of the damage to hydraulics we deal with is linked to length of use,” he says. Damage to hydraulics can be caused by heavy landings. Weaknesses may be discovered in a hydraulic part that means its life-cycle is shorter than originally envisaged. OEMs may issue service bulletins or component maintenance manual changes for a part to be replaced earlier than anticipated.
Aerotek performs major overhauls of hydraulic undercarriage and other hydraulic actuator systems, sometimes requiring total replacement of hydraulic systems on older aircraft. “We have a supply chain that enables us to carry out very complex repairs,” May says. “But we sometimes face difficulties getting the parts we need.”
Reverse engineering of parts thus is sometimes necessary. Aerotek has worked with Cranfield University in the UK to perform reverse engineering of hydraulic components that are not otherwise available, test them and ultimately have them approved by the OEM and put into service. Staff at Aerotek receive intensive practical training in how to repair hydraulic systems. “Working on hydraulics on the production line or in manufacturing is not the same as carrying out MRO,” May points out.
Some of the aircraft the company services are 30-40 years old, and taking apart the landing gear represents a different challenge than for newer aircraft, he says. OEM documentation will have changed over the years—and regulations, too. “With a legacy fleet, each landing gear is different,” May says. Quality procedures to maintain such aircraft are stringent and based on the regulatory requirements of the British Civil Aviation Authority and European Aviation Safety Agency. Documentation of aircraft systems tends to be comprehensive, but OEMs will issue service bulletins indicating new repairs or overhaul requirements for hydraulics frequently.
Hydraulic systems will be made available by suppliers for the duration of the aircraft’s life, but lead times can be lengthy to secure scarce parts. To save time, Aerotek will sometimes search for a part on the market, bring it in, overhaul it, and use it for a repair. Specializing in hydraulics for older aircraft in the MRO market is useful, May says: “Historically, we have been able to corner the market in certain aircraft. For example, we cornered the market in Shorts.” Aerotek is moving into hydraulics repair for older A320s and 737s “because the manufacturers are less interested in doing that themselves,” he says.
Aerotek has also just set up a joint-venture facility with Sika Global, duplicating its UK hydraulics MRO capability in Bangalore, India. “This is because there is no company specializing in the area of hydraulics and landing gear in the country,” notes May. “But over the next 20 years, the biggest market for growth in aviation is India—and quite a lot of the operators start with fleets of older, cheaper planes.”
For newer aircraft, manufacturers are developing more sophisticated and powerful hydraulics. For example, Eaton introduced the first 5,000-psi commercial hydraulic pumps in the early 2000s on the Airbus A380.
Eaton also is supporting the development of more electric aircraft using a zonal concept, which ultimately will lead to the replacement of all three distributed hydraulic systems with a number of hydraulic powerpacks. Eaton currently offers a zonal powerpack that replaces the third hydraulic system needed for fly-by-wire flight controls with strategically placed, electrically driven powerpacks. This allows the use of standard flight controls instead of more expensive and less reliable emergency back-up electro-hydrostatic flight controls.
As the industry moves toward broader use of variable-frequency AC and high-voltage DC networks, Eaton is developing strategies to integrate electrical motors and associated electric/electronic drives within hydraulic systems and components. The company has also been developing products such as maintenance-free accumulators, which are already qualified and flying on the A380 and A350.
“We anticipate that the next generation of aircraft will embed more sensors to predict maintenance actions to improve aircraft operational reliability,” Devan says. “Eaton is currently working on advanced debris monitoring and oil-condition monitoring to meet this emerging trend.”