MIL-STD-1796A(USAF)
4.3 Criticality and incremental verification.
The level of verification and time phasing of tests or other verifications will depend on the criticality of the hardware/function. TABLE II shows typical test timing requirements.
TABLE II. Timing of environmental and life testing.
Flight critical |
Safety critical |
Non�Flight and Non� Safety critical |
|
Complete prior to formal integration testing |
SOF portion of environmental qual |
||
Complete prior to first flight |
Full environmental qual and 25% of life testing |
SOF portion of environmental qual. |
SOF portion of environmental qual. |
Complete prior to production decision |
Full environmental qual and full life testing |
Full environmental qual and full life testing |
Most of environmental qual and life testing, to be determined based on cost and schedule risk |
Complete prior to delivery of production items/fielding |
All |
All |
All |
Hardware items may be grouped into criticality categories such as flight critical and safety critical, through the failure modes, effects and criticality analysis (FMECA) process. Guidance for conducting FMECAs is in MIL-HDBK-338.
To prevent loss of life and aircraft, safety critical functions must be designed to assure that a situation cannot occur that leads to loss of the required performance. Less severe than safety critical functions, but still very important, is the need to avoid loss of the ability to perform an assigned mission because of failures in the system. Redundancy is used in flight critical, safety critical, and some mission critical functions as a method to reduce the probability of a loss of required performance.
For example, if presentation of airspeed to the pilot is a safety critical function performed by avionics, the system design must be assessed to determine if level of redundancy, reliability, failure detection, etc. are adequate to meet safety requirements. The hardware which performs this function must meet the requirement of the safety critical column of TABLE II.
Maintenance trade-offs are also based on the life predictions and the criticality of the hardware items. For example, life limited items which are safety critical or mission critical are usually assigned preventive maintenance at designated time intervals.
Durability critical components are defined in MIL-STD-1798 as primarily mechanical items
"whose failure may entail costly maintenance and or part repair and replacement of which, if
11
For Parts Inquires submit RFQ to Parts Hangar, Inc.
© Copyright 2015 Integrated Publishing, Inc.
A Service Disabled Veteran Owned Small Business