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Effect of mixing MIL-H-5606 into MIL-H-83282

Aviation Mechanic Airframe (AMA) practice question 14 of 15 on Hydraulic and Pneumatic Systems. ACS element AM.II.F.R3 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONContamination of the fire-resistant fluid MIL-H-83282 with MIL-H-5606 may have what effect?

  1. Amake the MIL-H-83282 non-fire-resistant
  2. Bmake the MIL-H-83282 more fire resistant
  3. Chave no effect; the two are interchangeable
Show the answer and explanation

Correct answer: A. make the MIL-H-83282 non-fire-resistant

  • A — correct Hydraulic fluids are not necessarily compatible, and contamination of MIL-H-83282 with MIL-H-5606 may render the MIL-H-83282 non-fire-resistant.
  • B — incorrect MIL-H-5606 is the flammable fluid that MIL-H-83282 was developed to replace, so adding it can only reduce fire resistance.
  • C — incorrect The interchangeable pair is MIL-H-5606 and its rust-inhibited version MIL-H-6083; MIL-H-83282 is a different fluid whose fire resistance is lost when contaminated.

BACKGROUND

When servicing a hydraulic system, the technician must be certain to use the correct category of replacement fluid, because hydraulic fluids are not necessarily compatible. MIL-H-83282 is a fire-resistant hydrogenated polyalphaolefin-based fluid developed in the 1960s to overcome the flammability characteristics of MIL-H-5606, and contamination of MIL-H-83282 with MIL-H-5606 may render the MIL-H-83282 non-fire-resistant. MIL-H-83282 is significantly more flame resistant than MIL-H-5606, although it has a disadvantage of high viscosity at low temperature and is generally limited to -40 degrees F; it can be used in the same system and with the same seals, gaskets, and hoses as MIL-H-5606. Petroleum-based and phosphate ester-based fluids will not mix at all, and if an aircraft hydraulic system is serviced with the wrong type fluid the system must be immediately drained and flushed and the seals maintained according to the manufacturer's specifications.

STUDY TIP

Separate two different ideas: seal and hose compatibility between MIL-H-5606 and MIL-H-83282, and the loss of the fire-resistant property when the two are mixed.

KEY POINTS

  • Mixing MIL-H-5606 into MIL-H-83282 can destroy the fire resistance of MIL-H-83282.
  • MIL-H-5606 and MIL-H-6083 are the truly interchangeable pair.
  • Servicing with the wrong fluid type calls for immediate draining, flushing, and seal attention.

SOURCES

  • sources/ama-airframe/ch12.txt "Types of Hydraulic Fluids"
  • sources/ama-airframe/ch12.txt "Polyalphaolefin-Based Fluids"
  • sources/ama-airframe/ch12.txt "Intermixing of Fluids"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.