Per RADC-TR-80-299, the factors identified as having the highest importance into the development of the ARW environmental factor are random vibration, sine wave vibration, and temperature shock. Also reported to have a significant influence are low temperature, loads shock, humidity, temperature/altitude/humidity, dust/sand and EME. However, since MIL-HDBK-217F, Notice 2 environmental factors are based upon a merging of failure rate data reported from a variety of applications in a particular environment compared to data reported from a ground, benign environment, it is not possible to derive a mathematical expression linking the vibration level to a quantitative environmental factor. One still may be able to argue for a reduced environmental factor if the effects due to vibration have been minimized, but statistical support for this modification is another matter.

If you have flexibility in your reliability prediction approach, you may want to consider the 217Plus methodology. This methodology uses the actual expected operating temperature, temperature cycling rate, and vibration levels as inputs to the failure rate models.

Richard Wisniewski,
Senior Reliability Engineer
Reliability Information Analysis Center (RIAC)

Please note that the RIAC is currently in the process of being transitioned to the newly-formed Defense Systems Information Analysis Center (DSIAC). Quanterion Solutions, Inc., as the day-to-day operator of the RIAC, will continue in this capacity as part of the DSIAC in the technical areas of reliability, maintainability and quality (RMQ). Inquiries related to RMQ can continue to be made to the toll-free number at (877) 363-7422.