HYDRAULIC AND PNEUMATIC POWER
SYSTEMS FAA Questions and Answers 2025 A+
Which is a characteristic of synthetic base hydraulic fluid?
C- high flash point
Two types of hydraulic fluids currently being used in civil
aircraft are
A- mineral base and phosphate ester base
Which of the following lists only desirable properties of a
good hydraulic fluid?
B- Low viscosity, chemical stability, high flash point, high fire
point.
Characteristics of MIL-H-8446 (Skydrol 500 A & B) hydraulic
fluid are
B- light purple color, phosphate ester base, fire resistant, butyl
rubber seals
Where can information be obtained about the compatibility of
fire resistant hydraulic fluid with aircraft materials?
A- Fluid manufacturer's technical bulletins.
Characteristics of MIL-H-5606 hydraulic fluid are
C- red color, petroleum base, will burn, uses synthetic rubber
seals
Characteristics of MIL-H-7644 hydraulic fluid are
A- blue color, vegetable base, will burn, natural rubber seals
,If an aircraft hydraulic system requires mineral base
hydraulic fluid, but phosphate ester base hydraulic fluid is
used, what will be the effect on the system?
A- System will be contaminated, fluids will not blend, and the
seals will fail.
What is used to flush a system normally serviced with MIL-H-
5606 hydraulic fluid?
A- Naphtha or varsol
Components containing phosphate ester-base hydraulic fluid
may be cleaned with
C- Stoddard solvent
How can the proper hydraulic fluid be used in an airplane be
determined?
A- consult the aircraft manufacturer's service manual.
Phosphate ester base hydraulic fluid is very susceptible to
contamination from
C- water in the atmosphere
(1) Materials which are Skydrol compatible or resistant
include most common aircraft metals and polyurethane and
epoxy paints.
(2) Skydrol hydraulic fluid is compatible with nylon and
natural fibers.
Regarding the above statements,
A- both No. 1 and No. 2 are true
Which seals are used with petroleum base hydraulic fluids?
, A- Buna-N
Which seal/material is used with phosphate ester base
hydraulic fluids?
C- Butyl rubber
One of the main advantages of skydrol is its
A- wide operating tempurate
Hydraulic system thermal relief valves are set to open at
C- higher pressure than the system relief valve
Although dents in the heel of a bend are not permissible the
they are acceptable in the remainder of a hydraulic tube
providing they are less than what percent of the tube
diameter?
B- 20
A common cause of slow actuating of hydraulic components
is
B- internal leakage in the actuating unit
Teflon hose that has developed a permanent set from being
exposed to high pressure or temperature should
A- not be straightened or bent further
If an aircraft's constant pressure hydraulic system cycles
more frequently than usual and no fluid leakage can be
detected, the most probable cause is
A- low accumulator air preload
SYSTEMS FAA Questions and Answers 2025 A+
Which is a characteristic of synthetic base hydraulic fluid?
C- high flash point
Two types of hydraulic fluids currently being used in civil
aircraft are
A- mineral base and phosphate ester base
Which of the following lists only desirable properties of a
good hydraulic fluid?
B- Low viscosity, chemical stability, high flash point, high fire
point.
Characteristics of MIL-H-8446 (Skydrol 500 A & B) hydraulic
fluid are
B- light purple color, phosphate ester base, fire resistant, butyl
rubber seals
Where can information be obtained about the compatibility of
fire resistant hydraulic fluid with aircraft materials?
A- Fluid manufacturer's technical bulletins.
Characteristics of MIL-H-5606 hydraulic fluid are
C- red color, petroleum base, will burn, uses synthetic rubber
seals
Characteristics of MIL-H-7644 hydraulic fluid are
A- blue color, vegetable base, will burn, natural rubber seals
,If an aircraft hydraulic system requires mineral base
hydraulic fluid, but phosphate ester base hydraulic fluid is
used, what will be the effect on the system?
A- System will be contaminated, fluids will not blend, and the
seals will fail.
What is used to flush a system normally serviced with MIL-H-
5606 hydraulic fluid?
A- Naphtha or varsol
Components containing phosphate ester-base hydraulic fluid
may be cleaned with
C- Stoddard solvent
How can the proper hydraulic fluid be used in an airplane be
determined?
A- consult the aircraft manufacturer's service manual.
Phosphate ester base hydraulic fluid is very susceptible to
contamination from
C- water in the atmosphere
(1) Materials which are Skydrol compatible or resistant
include most common aircraft metals and polyurethane and
epoxy paints.
(2) Skydrol hydraulic fluid is compatible with nylon and
natural fibers.
Regarding the above statements,
A- both No. 1 and No. 2 are true
Which seals are used with petroleum base hydraulic fluids?
, A- Buna-N
Which seal/material is used with phosphate ester base
hydraulic fluids?
C- Butyl rubber
One of the main advantages of skydrol is its
A- wide operating tempurate
Hydraulic system thermal relief valves are set to open at
C- higher pressure than the system relief valve
Although dents in the heel of a bend are not permissible the
they are acceptable in the remainder of a hydraulic tube
providing they are less than what percent of the tube
diameter?
B- 20
A common cause of slow actuating of hydraulic components
is
B- internal leakage in the actuating unit
Teflon hose that has developed a permanent set from being
exposed to high pressure or temperature should
A- not be straightened or bent further
If an aircraft's constant pressure hydraulic system cycles
more frequently than usual and no fluid leakage can be
detected, the most probable cause is
A- low accumulator air preload
