Fluid Lines and Fittings Oral Exam Questions and Answers
Rehearse fluid lines and fittings by explaining the choice of material, connection, and inspection method in your own words. These practice questions are built from the ACS—not presented as questions assigned for your test.
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What should my answer explain?
Use the prompts below to practice explaining a line assembly from identification through installation and inspection. Each prompt names the ACS element it addresses, and each answer points to the relevant FAA handbook pages.
Keep closely related ideas separate while rehearsing: tubing size versus hose designation, a flared connection versus a flareless connection, and a sound flare versus an attempt to compensate for a defect. For a real aircraft task, read the applicable maintenance instructions rather than treating this practice set as an installation procedure.
For the wider exam, read the General oral questions overview. Use the ACS codes guide when reviewing the ACS codes on your Airman Knowledge Test Report (AKTR).
Which ACS elements do these questions practice?
The table identifies the elements used for the practice questions below. It is not a prediction of your assigned questions.
| ACS element | Study focus |
|---|---|
| AM.I.D.K1 | Tubing and hose materials, applications, sizes, and fittings. |
| AM.I.D.K2 | Rigid line or flexible hose material identification. |
| AM.I.D.K3 | Rigid line fabrication, installation, and inspection techniques/practices. |
| AM.I.D.K4 | Flexible hose fabrication, installation, and inspection techniques/practices. |
| AM.I.D.K5 | Importance of using a torque wrench when securing fluid hose and line fittings. |
| AM.I.D.R5 | A twisted hose. |
Which oral exam questions can I practice?
These ten practice questions are original study prompts built from ACS elements; they are not actual FAA test questions. The short explanations are study answers, not complete aircraft maintenance procedures.
1. When would you use rigid tubing rather than flexible hose?
ACS: AM.I.D.K1
Metal tubing is used in stationary applications and where long, relatively straight runs are possible. Flexible hose is generally used with moving parts or considerable vibration; it can also connect sections of metal tubing. Replacement tubing should have the same size and material as the original.
FAA-H-8083-30B, General, p. 9-1 · FAA-H-8083-30B, General, p. 9-16
2. What do a tubing size number and a hose dash number tell you?
ACS: AM.I.D.K1
Metal tubing is sized by outside diameter in sixteenths of an inch: number 6 is 3/8 inch and number 8 is 1/2 inch. Wall thickness also matters; inside diameter equals outside diameter minus twice the wall thickness. The handbook’s hose size-designation section says the dash number “indicates the size tubing with which the hose is compatible. It does not denote inside or outside diameter.” When the dash number of the hose corresponds with the dash number of the tubing, the proper size hose is being used.
FAA-H-8083-30B, General, p. 9-2 · FAA-H-8083-30B, General, p. 9-19
3. How do you positively identify the material of replacement tubing?
ACS: AM.I.D.K2
Compare the replacement tubing’s code markings with the markings on the tubing being replaced. Appearance can identify the broad material, but it may not distinguish particular steel or aluminum alloys. Large aluminum tubing has a stamped alloy designation; small tubing may be stamped, but more often uses a color code. If code markings are hard or impossible to read, testing material samples for hardness may be necessary.
FAA-H-8083-30B, General, p. 9-1 · FAA-H-8083-30B, General, p. 9-2
4. What flare angle does the handbook specify for an aircraft tubing flaring tool?
ACS: AM.I.D.K3
The aircraft tubing flaring tool has male and female dies that produce a 35° to 37° flare. The handbook states: “Under no circumstance is it permissible to use an automotive-type flaring tool that produces a flare of 45°.” Aircraft tubing commonly uses either single or double flares.
FAA-H-8083-30B, General, p. 9-4 · FAA-H-8083-30B, General, p. 9-3
5. What condition should a flare be in before installation, and can extra torque correct it?
ACS: AM.I.D.K3
The flare and tubing must be free of cracks, dents, nicks, scratches, and other defects. A crooked flare results from tubing that was not cut squarely. The handbook states: “If a flare is not made properly, flaws cannot be corrected by applying additional torque when tightening the fitting.”
FAA-H-8083-30B, General, p. 9-4
6. How can you distinguish an AN flared fitting from an MS flareless fitting?
ACS: AM.I.D.K1
An AN flared fitting has a cone at its end; an MS flareless fitting has a straight end. They are different fittings and are not interchangeable. The MS flareless fitting has three parts: a body, a sleeve, and a nut. Its sleeve cuts into the tube’s outside surface as the body and nut are joined.
FAA-H-8083-30B, General, p. 9-9
7. Why use a torque wrench on a fluid-line fitting rather than tightening by feel?
ACS: AM.I.D.K5
Using a torque wrench with the prescribed torque values prevents overtightening or undertightening. Both matter: overtightening “may badly damage or completely cut off the tube flare, or it may ruin the sleeve or fitting nut,” and undertightening “may allow the line to blow out of the assembly or to leak under system pressure.” The line should be properly aligned before the fittings are tightened. The handbook warns: “Do not pull the installation into place with torque on the nut.” Its Figure 9-20 torque values apply to flared-type fittings only.
FAA-H-8083-30B, General, p. 9-12 · FAA-H-8083-30B, General, p. 9-10
8. How do Buna-N, neoprene, and butyl differ in fluid compatibility?
ACS: AM.I.D.K1
Buna-N has excellent petroleum resistance; neoprene has less petroleum resistance but better abrasion resistance. For both, the handbook says: “Do not use for phosphate ester base hydraulic fluid (Skydrol™).” Butyl is an excellent material for that fluid, but its warning is: “Do not use with petroleum products.”
FAA-H-8083-30B, General, p. 9-16
9. What signs of flexible-hose deterioration call for replacement?
ACS: AM.I.D.K4
Check the hose and assembly at each inspection period. Signs of deterioration and reasons for replacement include leakage, cover or braid separation from the inner tube, cracks, hardening, lack of flexibility, and excessive cold flow. Cold flow means deep, permanent impressions caused by hose clamps or supports.
FAA-H-8083-30B, General, p. 9-18
10. What indicates a twisted hose, and what risk does the handbook identify?
ACS: AM.I.D.R5
Inspect the identification stripe along the hose; it should not spiral around it. The handbook states: “Hoses must be installed without twisting to avoid possible rupture of the hose or loosening of the attaching nuts.” Swivel connections at one or both ends relieve twist stresses.
FAA-H-8083-30B, General, p. 9-21
How do I answer it out loud?
Rehearse in three passes: first, identify tubing, hose, sizes, and fitting types; next, explain flaring and torque; finally, discuss hose compatibility, deterioration, and twisting. Revisit the FAA pages beside any answer you cannot explain clearly.
How should I check my practice answer?
Choose one prompt, close the answer, and respond out loud. Then compare your response with every point in the answer. For the hose-deterioration question, check that you named the entire list; for the sizing question, check that you distinguished tubing outside diameter from hose compatibility.
Check the explanation in the handbook during study, then close it for the spoken rehearsal. The ACS states that reference material is not allowed for answering oral questions.
“the applicant is not allowed to use any reference material to answer the oral questions asked by the examiner.”
What else should I know?
Are these the exact questions I will receive from a DME?
No. These are original practice questions built from the ACS elements shown beside each prompt, not a list of questions assigned for your test.
What does a hose dash number tell you?
The FAA handbook says the dash number “indicates the size tubing with which the hose is compatible. It does not denote inside or outside diameter.” When the hose and tubing dash numbers correspond, the proper size hose is being used.
Are AN flared and MS flareless fittings interchangeable?
No. The FAA handbook states that AN flared fittings and MS flareless fittings are different and are not interchangeable.
Can extra torque correct a poorly formed flare?
No. The FAA handbook states: “If a flare is not made properly, flaws cannot be corrected by applying additional torque when tightening the fitting.”
How can I rehearse the spoken answer?
DMEReady is an AI voice examiner for A&P oral practice in your phone or computer browser. You answer out loud, and it asks follow-up questions the way a DME would. After each session, the report shows what you covered, what you missed, what a complete answer includes, and where to read in the FAA handbooks. The first drill is free with no sign-up. It is an AI examiner, not a human DME. DMEReady is independent and is not affiliated with or endorsed by the FAA; it does not predict or guarantee exam results.
Start your free drillWhich guide should I read next?
- Ground Operations and Servicing Oral Exam Questions
- Hydraulic and Pneumatic Systems Oral Exam Questions
Which sources support these answers?
References show the printed handbook pages. The links open the corresponding PDF pages.
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