MIL-STD-1798 Mechanical Equipment And Subsystems Integrity ProgramThe purpose of this standard is to describe the general process to achieve and maintain the physical and functional integrity of the mechanical elements of aircraft systems. The goal of this integrity program is to achieve the desired level of safety and aircraft availability at the most economic cost across the life cycle of the weapon system. This standard allows the process to be tailored in a competitive environment to meet specific equipment, subsystem, and/or system requirements. The Mechanical Equipment and Subsystems Integrity Program MECSIP is implemented in the planning process and continued until retirement of the system.

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MIL-STD-1798C

5.3.2.4 Thermal/environmental analyses and tests.

These analyses shall be conducted to determine the steady-state and transient thermal environments for individual elements of the system. This analysis will subdivide the aircraft into zones exposed to the same environment (both natural and induced). Then specific environmental extremes for both operating and withstanding will be defined. Environmental conditions to consider include all those environmental conditions addressed by MIL-STD-810. These natural and induced environments shall be used in the design, analyses, and testing (e.g., strength, durability, damage tolerance, vibration/dynamics, corrosion resistance, etc.) of the individual components and/or systems.

5.3.2.5 Stress/strength analyses.

These analyses shall be conducted to determine the stresses, deformations, and margins of safety which result from the applications of design conditions, loads, and environments. These analyses are required for verification of strength.

5.3.2.6 Durability analyses.

Durability analyses shall be conducted on each MECSIP part classified as safety-, mission-, or durability-critical, for the planned service life of those components. The analysis is a risk reduction task to verify the design is likely to meet the service life requirements when subjected to the operational usage and environments. Analyses shall be conducted early in the

acquisition phase to support design concept development, material selection, and weight/cost/performance trade studies. Early analyses will enable identification of failure modes

and sensitive areas, particularly those with potential for early fatigue, wear, environmental

degradation, or thermal distress. Allowable limits for critical failure modes, cracking, wear, chafing, and environmental degradation must be defined as part of these analyses. Early analysis shall be emphasized to minimize occurrences of deficiencies during subsequent development and functional testing. Material and process data required to support analytical methods shall be generated in accordance with 5.3.3.1.

The durability analyses may consider the affects of scheduled maintenance. The analyses shall consider material variability, initial manufacturing quality, and functional limits for each critical failure mode. Components shall be designed and analyzed using appropriate factors, to

account for variations in material properties, processes, manufacturing, etc. A minimum factor of four times the required service life using nominal properties, tolerances, etc., will be applied

for safety-critical mechanical components. Mission- and durability-critical components shall use

a minimum factor of twice the required service life. Certain applications that use a high durability margin approach (e.g., door drive systems) require more stringent factors (e.g.,

landing gear minimum is 4 life factors, flight control actuators as high as 7). Individual

component analytical results should be used to prove the available economic life of the total system is at least equal to the required operational service life specified in the contractual documents.

5.3.2.7 Damage tolerance analyses.

Damage tolerance design and analyses shall be conducted, for all parts using a damage tolerance design approach, to substantiate the ability of the identified components to continue to perform safely in the presence of material, manufacturing, processing, or handling- or operationally-induced damage for the minimum required maintenance-free period of unrepaired usage.