Commercial, cargo, private, corporate and military aircraft rely extensively on both high pressure and low pressure hydraulic lines for their proper and safe operation. For instance, the control surfaces on high performance aircraft are mechanically actuated through hydraulic control systems. The extension and retraction of land gear are also typically hydraulically actuated. Further, many additional functions of an aircraft, some critical and some less than critical, are operative through hydraulics.
When a leak develops in fight critical hydraulic control systems, the associated aircraft is typically grounded until the leak can be repaired. On many commercial, cargo, private, corporate and military aircraft, the hydraulic tubing that transports the pressurized fluid is comprised of rigid stainless steel, titanium and/or aluminum wherein the aluminum tubing is typically reserved for low pressure usage and the higher strength materials are used in high pressure hydraulic lines. A typical hydraulic line may be bent in a multitude angles and places as it snakes itself around the various components and structure of an aircraft from its proximal to distal ends whereat it is connected or coupled to other conduit or other components of the hydraulic system.
As can be appreciated, the probability that any one hydraulic line will fail of the hundreds if not thousands on a particular aircraft is extremely low. Accordingly, airlines do not typically stock the various hydraulic line sections as repair parts at its various repair facilities around the country and the world. To repair damage or a leak, the necessary section of hydraulic tubing is ordered from the appropriate manufacturer who specially fabricates the section as the typical aircraft repair facility does not have the specialized equipment available for bending hydraulic tubing without unintentionally crimping or otherwise damaging the tubing.
From the time the replacement tubing section is ordered to the time of its delivery and installation can take anywhere from days to weeks costing an airline thousands if not hundred of thousands of dollars because of the grounded aircraft.
One known work around that minimizes the downtime of an aircraft is to replace the leaking portion of a rigid pressure tube section with a temporary flexible tube replacement thus minimizing the aircraft's downtime. Procedurally, the leaking portion is cut from the affected hydraulic line, fittings having threaded ends are swaged or otherwise secured into place on the line, and a suitable flexible tube with corresponding threaded ends is secured to the fittings to complete replacement of the damaged portion. Current FAA rules classify a flexible hose repair of high pressure hydraulic lines as only temporary and permit its use for no more than 40 hours of flight time before it must be replaced with a permanent repair. Even under the best conditions, the affected aircraft must undergo two costly repair procedures.