Fluid Lines & Fittings
Fluid Lines & Fittings is a core knowledge area on the AMT — General FAA written exam. This hub collects our 16 in-depth, ACS-aligned fluid lines & fittings articles — each written in plain English and grounded in the official FAA handbooks. Work through them below, then drill the topic with practice questions.
Fluid Line Sizing: OD vs ID and Dash Number Notation
Aviation fluid lines are identified by dash numbers tied to outside or inside diameter—understanding OD vs ID and the dash numbering system is essential for correct line selection, maintenance, and FAA knowledge test success.
Rigid Fluid Line Materials and Identification (Aluminum, Steel, Titanium)
Aircraft rigid fluid lines are manufactured from aluminum alloy, steel, or titanium tubing, each chosen for specific pressure, temperature, and weight requirements; correct material identification and selection are critical to airworthiness.
AN and MS Flareless Fitting Standards and Applications
AN and MS flareless fittings provide secure, leak-free connections in aircraft hydraulic, fuel, and pneumatic systems without requiring a flared tube end — understanding their standards, installation steps, and limits is essential for any AMT.
Flexible Hose Types and Construction (Rubber, PTFE, Teflon)
Aircraft flexible hoses—rubber, PTFE, and Teflon—each serve distinct pressure, temperature, and fluid-compatibility roles; understanding their construction and markings is essential for safe installation and FAA knowledge test success.
Single-Flare vs Double-Flare Tube End Fabrication
Single-flare and double-flare tube end fabrication are critical skills for aircraft fluid-line maintenance; choosing the correct type and executing it properly ensures leak-free, structurally sound connections.
B-Nut and Sleeve Installation for Flareless Fittings
Flareless fittings use a sleeve and B-nut to create a leak-free hydraulic or fuel line connection without flaring the tube — correct installation technique is critical for safety and FAA knowledge test success.
45-Degree Flare Fitting Assembly and Torque Procedures
Learn how to properly assemble and torque 45-degree flare fittings used in aircraft fluid systems, including preparation steps, torque values, and common inspection pitfalls covered on the FAA AMT General knowledge test.
Tube Bending Techniques and Minimum Bend Radius Requirements
Proper tube bending prevents kinks, wrinkles, and structural failure in aircraft fluid lines; mastering minimum bend radius and correct technique is essential for airworthy plumbing repairs.
Hose Clamping, Routing, and Support Spacing Requirements
Aircraft hose installation demands precise clamping intervals, correct routing away from heat and chafe hazards, and proper support spacing to prevent vibration fatigue and fluid system failures.
Fluid Line Inspection: Dents, Kinks, Corrosion, and Chafing Criteria
Fluid lines are the circulatory system of an aircraft—this article covers the FAA inspection criteria for dents, kinks, corrosion, and chafing so technicians know exactly when to repair or replace a line.
Swaged and Reusable End Fittings for Flexible Hose
Swaged and reusable end fittings allow flexible hose assemblies to be terminated securely for aircraft hydraulic, fuel, and pneumatic systems; understanding their construction, inspection, and correct installation is essential for safe fluid-line maintenance.
Color Coding and Identification Markings on Aircraft Fluid Lines
Aircraft fluid lines use standardized color codes, bands, and letter codes so maintenance technicians can instantly identify a line's contents and function—critical for both safety and correct servicing.
Pressure Ratings and Proof Test Requirements for Fluid Lines
Pressure ratings, burst limits, and proof test requirements for aircraft fluid lines govern safe system design and post-repair airworthiness; understanding these values is essential for every AMT.
Fluid Line End Preparation: Cutting, Deburring, and Cleaning Procedures
Proper fluid line end preparation—cutting, deburring, and cleaning—is critical for leak-free hydraulic, fuel, and pneumatic systems; errors here can cause fittings to fail or contaminate entire aircraft systems.
Quick-Disconnect Fittings: Types, Operation, and Maintenance
Quick-disconnect fittings allow fluid lines to be rapidly coupled or uncoupled without tools or fluid loss, making them critical for aircraft maintenance efficiency and system integrity.
Torque Values and Leak Testing Procedures for Fluid Line Connections
Proper torque values and leak testing procedures for fluid line connections are critical to aircraft airworthiness — under- or over-torquing fittings and missing leaks can lead to system failures and fires.
More AMT — General subjects
Articles are original summaries grounded in the public-domain FAA handbooks and cite their source. ACS-aligned study aids — not a substitute for the official handbooks or regulations.