Sec. 25.1435 - Hydraulic systems.
(a) Element design. Each element
of the hydraulic system must be designed to:
(1) Withstand the proof pressure without
permanent deformation that would prevent it from performing its intended
functions, and the ultimate pressure without rupture. The proof and
ultimate pressures are defined in terms of the design operating pressure (DOP)
as follows:
------------------------------------------------------------------------
Proof Ultimate
Element (xDOP) (xDOP)
------------------------------------------------------------------------
1. Tubes and fittings............................. 1.5 3.0
2. Pressure vessels containing gas:
High pressure (e.g., accumulators).............. 3.0 4.0
Low pressure (e.g., reservoirs)................. 1.5 3.0
3. Hoses.......................................... 2.0 4.0
4. All other elements............................. 1.5 2.0
------------------------------------------------------------------------
(2) Withstand, without deformation that
would prevent it from performing its intended function, the design
operating pressure in combination with limit structural loads that may be
imposed;
(3) Withstand, without rupture, the
design operating pressure multiplied by a factor of 1.5 in combination
with ultimate structural load that can reasonably occur simultaneously;
(4) Withstand the fatigue effects of all
cyclic pressures, including transients, and associated externally induced
loads, taking into account the consequences of element failure; and
(5) Perform as intended under all
environmental conditions for which the airplane is certificated.
(b) System design. Each hydraulic
system must:
(1) Have means located at a flightcrew
station to indicate appropriate system parameters, if
(i) It performs a function necessary for
continued safe flight and landing; or
(ii) In the event of hydraulic system
malfunction, corrective action by the crew to ensure continued safe flight
and landing is necessary;
(2) Have means to ensure that system
pressures, including transient pressures and pressures from fluid
volumetric changes in elements that are likely to remain closed long
enough for such changes to occur, are within the design capabilities of
each element, such that they meet the requirements defined in
§25.1435(a)(1) through (a)(5);
(3) Have means to minimize the release
of harmful or hazardous concentrations of hydraulic fluid or vapors into
the crew and passenger compartments during flight;
(4) Meet the applicable requirements of
§§25.863, 25.1183, 25.1185, and 25.1189 if a flammable hydraulic fluid is
used; and
(5) Be designed to use any suitable
hydraulic fluid specified by the airplane manufacturer, which must be
identified by appropriate markings as required by §25.1541.
(c) Tests. Tests must be
conducted on the hydraulic system(s), and/or subsystem(s) and elements,
except that analysis may be used in place of or to supplement testing,
where the analysis is shown to be reliable and appropriate. All internal
and external influences must be taken into account to an extent necessary
to evaluate their effects, and to assure reliable system and element
functioning and integration. Failure or unacceptable deficiency of an
element or system must be corrected and be sufficiently retested, where
necessary.
(1) The system(s), subsystem(s), or
element(s) must be subjected to performance, fatigue, and endurance tests
representative of airplane ground and flight operations.
(2) The complete system must be tested
to determine proper functional performance and relation to the other
systems, including simulation of relevant failure conditions, and to
support or validate element design.
(3) The complete hydraulic system(s)
must be functionally tested on the airplane in normal operation over the
range of motion of all associated user systems. The test must be conducted
at the system relief pressure or 1.25 times the DOP if a system pressure
relief device is not part of the system design. Clearances between
hydraulic system elements and other systems or structural elements must
remain adequate and there must be no detrimental effects.
[Doc. No. 28617, 66 FR 27402, May 16, 2001]