Hydraulic Hose Replacement on a 3,000-psi System
A mechanic is replacing an 18-inch, 1/4-inch-ID hydraulic hose on a 3,000-psi system. The only approved-looking replacement in stock is a 24-inch hose marked SAE 100R5 with a working pressure of 3,000 psi and 45-degree flare fittings. The original hose used 37-degree aviation flare fittings. The new routing requires a 2.0-inch centerline bend radius; the hose outside diameter is about 0.50 inch, and the manufacturer’s minimum bend radius for the original hose is 3.0 inches. The mechanic plans to support the hose at one end only, route it within 4 inches of an exhaust stack without a heat shield, and torque the fittings using a generic automotive table. The aircraft is due for return to service.
1. Identify the fitting and pressure-rating discrepancies. Can this hose assembly be installed and approved for return to service?
Read the worked answer
Reject the assembly as proposed. A 37-degree aviation flare and a 45-degree automotive flare have different sealing cones and are not interchangeable; forcing them together can leak or crack the flare. The hose must use the correct approved end fittings. A 3,000-psi working-pressure marking alone does not make an SAE 100R5 hose an approved aircraft part; verify the hose specification, fluid compatibility, temperature rating, and aircraft or manufacturer approval. If approved data do not support this hose and fitting combination, obtain a properly rated aviation hose assembly. Do not sign it off just because the pressure rating matches system pressure.
2. Evaluate the bend radius and support/heat routing. What must be changed?
Read the worked answer
The 2.0-in centerline bend radius is below the 3.0-in manufacturer minimum, so it is too tight and can kink, restrict flow, or fatigue the hose. Re-route or use a hose with an approved smaller minimum bend radius. Support the hose at intervals allowed by the manufacturer and AC 43.13-1B (commonly not more than 24 in), with clamps that do not crush the hose. Four inches from an exhaust stack without a heat shield is not acceptable; maintain the required clearance or install an approved heat shield or fire sleeve. Leave enough slack for pressure and movement, but avoid sharp bends and chafe.
3. What should the mechanic do about torque and pressure testing before signing the logbook?
Read the worked answer
Use the hose and fitting manufacturer’s torque values with a calibrated torque wrench; a generic automotive table is not acceptable. If a crowfoot or extension changes the lever arm, correct the applied torque. Assemble per approved instructions, then proof or pressure-test to the manufacturer’s or AC 43.13-1B procedure and inspect for leaks, weeping, and damaged fittings. Record the hose part number, test results, and approval for return to service in the maintenance record. If approved torque or test data are unavailable, stop and obtain them before return to service.