All aircraft, from the smallest trainers to the largest transports , have systems to direct the flow of fluids from their source to the units requiring them. These systems consist of hoses, tubing, fittings, and connectors. Aircraft fluid lines are usually made of metal tubing or flexible hose. Metal tubing (also called rigid fluid lines) is used in stationary applications and where long, relatively straight runs are possible. They are widely used in aircraft for fuel, oil, coolant, oxygen, instrument, and hydraulic lines.
Flexible hose is generally used with moving parts or where the hose is subject to considerable vibration. Occasionally, it may be necessary to repair or replace damaged aircraft fluid lines. Very often the repair can be made simply by replacing the tubing. However, if replacements are not available, the needed parts may have to be fabricated. Replacement tubing should be of the same size and material as the original tubing. All tubing is pressure tested prior to initial installation and is designed to withstand several times the normal operating pressure to which it is subjected. If a tube bursts or cracks, it is generally the result of excessive vibration, improper installation, or damage caused by collision with an object. All tubing failures should be carefully studied and the cause of the failure determined.
As a maintenance technician, understand the different types of fluid lines used, their applications, and the inspection and maintenance requirements of each. An error in the selection or installation of a component could result in damage to a unit, loss of fluid, or complete system failure. Regular inspection and time-specified replacements ensure continuous and safe operation.