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Design and construction changes |
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|  MIL-S-22518A(AS)
3.3.8
Design and construction changes.
3.3.8.1
Material substitutions. Material substitutions
shall be subject to the approval of the qualifying activity. The SAE
Index of Aeronautical Material Specification and ASTM Standard E527 (SAE
Designation J1086) Numbering Metals and Alloys (UNS) may be used as
guides for material substitutions.
3.3.8.2
Changes in design. No changes shall be made in the
design or materials of an ATS/AD model that has been qualified, in
accordance with this specification, except when the changes are approved
by the qualifying activity in accordance with DOD-STD-480.
3.3.8.3
Parts list. The parts list of the ATS/AD which
successfully completes the required qualification tests shall constitute
a requirement for production ATS/ADs. Departure from the approved
ATS/AD parts list in features of design and construction shall be governed
by the provisions herein for changes in design.
3.3.8.4
Responsibility for changes. Approval by the qualifying
activity of changes from the qualification test ATS/AD does not relieve
the contractor of full responsibility for any adverse results of such
changes.
Threaded parts.
3.3.9
3.3.9.1
Straight screw threads. All conventional straight
screw threads shall conform to the requirements of MIL-S-8879 except for
electrical connections, thermocouple harness, fluid fittings and ground
and cut threads incorporated in proprietary parts which do not have
equivalent standards. All exceptions shall conform to MIL-S-7742.
Tapered pipe threads. Tapered pipe threads shall be
3.3.9.2
in accordance with MIL-P-7105 and shall be only for permanently plugging
drilled or cored openings.
Threaded inserts. All threaded connections In non-
3.3.9.3
ferrous materials shall have steel inserts which are suitably protected
from electrolytic corrosion. Fill and drain boss inserts shall be
designed to permit the use of standard gaskets or seals and standard
straight thread plugs.
3.3.9.4
Safetying. Provisions shall be made to prevent all
screws and screw parts from accidental loosening. Such parts shall be
safety wired or fitted with safety stop nuts, where applicable. All
other connections liable to be loosened by vibration shall be safetied
in a similar manner. If safetying is by wiring; it shall be in accordance
with MS33540. The use of lock nuts which incorporate non-metallic
inserts as a locking feature shall be avoided.
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