JAR 25.1435 Hydraulic systems
(a) Design. Each hydraulic system must be
designed as follows:
(1) Each element of the hydraulic
system must be designed to withstand the loads
due to the working pressure Pw, in the case of
elements other than pressure vessels or to the
limit pressure, PL, in the case of pressure
vessels, in combination with limit structure
loads which may be imposed without
deformation that would prevent it from
performing its intended function, and to
withstand without rupture, the working or limit
pressure loads multiplied by a factor of 1·5 in
combination with ultimate structural loads that
can reasonably occur simultaneously.
(i) Pw. The working pressure is
the maximum steady pressure in service
acting on the element including the
tolerances and possible pressure
variations in normal operating modes but
excluding transient pressures.
(ii) PL. The limit pressure is the
anticipated maximum pressure in service
acting on a pressure vessel, including the
tolerances and possible pressure
variations in normal operating modes but
excluding transient pressures.
(2) A means to indicate system pressure
and a means to indicate fluid quantity, both
located at a flight-crew member station, must
be provided for each hydraulic system that –
(i) Performs a function that is
essential for continued safe flight and
landing; or
(ii) In the event of hydraulic
system malfunction, requires corrective
action by the crew to ensure continued
safe flight and landing.
(3) Reserved.
(4) There must be means to ensure that
system pressures, including transient pressures
and pressures from fluid volumetric changes in
components which are likely to remain closed
long enough for such changes to occur –
(i) Will be within 90 to 110% of
pump average discharge pressure at each
pump outlet or at the outlet of the pump
transient pressure dampening device, if
provided; and
(ii) Except as provided in sub-paragraph
(a)(7), will not exceed 125%
of the design operating pressure,
excluding pressure at the outlets specified
in sub-paragraph (i) of this paragraph.
(See ACJ 25.1435(a)(4).) Design
operating pressure is the maximum steady
operating pressure.
(5) Each hydraulic element must be
installed and supported to prevent excessive
vibration, abrasion, corrosion, and mechanical
damage, and to withstand inertia loads. If a
hydraulic fluid which could be harmful to
occupants when liberated in any form is used,
there must be a means to prevent harmful or
hazardous concentration of the fluid or vapours
in the crew or passenger compartments during
flight.
(6) Means for providing flexibility
must be used to connect points in a hydraulic
fluid line between which relative motion or
differential vibration exists.
(7) Transient pressure in a part of the
system may exceed the limit specified in sub-paragraph
(a)(4)(ii) of this paragraph if –
(i) A survey of those transient
pressures is conducted to determine their
magnitude and frequency; and
(ii) Based on the survey, the
fatigue strength of that part of the system
is substantiated by analysis or tests, or
both.
(8) Each hydraulic pump must be
designed and installed so that loss of hydraulic
fluid to the pump cannot create a hazard that
might prevent continued safe flight and
landing. (See ACJ 25.1435 (a)(8).)
(9) The system must be designed to
avoid hazard to the aeroplane arising from the
effects of abnormally high temperatures which
may occur in certain parts of the system under
fault conditions. (See ACJ 25.1435 (a)(4).)
(10) The elements of the system must be
able to withstand the loads due to the pressure
[ given in Appendix K, for the proof ]
condition without leakage or permanent
distortion and for the ultimate condition
without rupture. Temperatures must be those
corresponding to normal operating conditions.
Where elements are constructed from materials
other than aluminium alloy, tungum, or
medium-strength steel, the Authority may
prescribe or agree other factors. The materials
used must in all cases be resistant to
deterioration arising from the environmental
conditions of the installation, particularly the
effects of vibration.
(11) Where any part of the system is
subject to fluctuating or repeated external or
internal loads, adequate allowance must be
made for fatigue.
(b) Tests
(1) A complete hydraulic system must
be static tested to show that it can withstand a
pressure of 1·5 times the working pressure
without a deformation of any part of the system
that would prevent it from performing its
intended function. Clearance between
structural members and hydraulic system
elements must be adequate and there must be
no permanent detrimental deformation. For the
purpose of this test, the pressure relief valve
may be made inoperable to permit application
of the required pressure.
(2) Compliance with JAR 25.1309 for
hydraulic systems must be shown by functional
tests, endurance tests, and analyses. The entire
system or appropriate subsystems must be
tested in an aeroplane or in a mock-up
installation to determine proper performance
and proper relation to other aeroplane systems.
The functional tests must include simulation of
hydraulic system failure conditions. The tests
must account for flight loads, ground loads,
and hydraulic system working, limit and
transient pressures expected during normal
operation, but need not account for vibration
loads or for loads due to temperature effects.
Endurance tests must simulate the repeated
complete flights that could be expected to
occur in service. Elements which fail during
the tests must be modified in order to have the
design deficiency corrected and, where
necessary, must be sufficiently retested.
Simulation of operating and environmental
conditions must be completed on elements and
appropriate portions of the hydraulic system to
the extent necessary to evaluate the
environmental effects. (See ACJ 25.1435
(b)(2).)
(3) Parts, the failure of which will
significantly lower the airworthiness or safe
handling of the aeroplane must be proved by
suitable testing, taking into account the most
critical combination of pressures and
temperatures which are applicable.
(c) Fire protection. Each hydraulic system
using flammable hydraulic fluid must meet the
applicable requirements of JAR 25.863, 25.1183,
25.1185 and 25.1189.
(d) The constructor must specify the
hydraulic fluid which is suitable to be used in the
aeroplane.
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