ANSI / VITA 51.1 & MIL-HDBK-217

ANSI / VITA 51.1 is an industry standard that provides consensus based modification factors for use with MIL-HDBK-217 Revision F, Notice 2. VITA 51.1 was developed prior to the launch in 2008 of the DoD-led effort to revise MIL-HDBK-217. It provided uniformity of practice for use of MIL-HDBK-217 Rev F, Notice 2 and consensus based modification factors for the models. MIL-HDBK-217 Rev F, Notice 2 was published in 1995 and has become obsolete for many technologies. Most companies that use the methodology have supplemented it with internally developed modification factors based on product testing and/or field failure data. The effort to revise MIL-HDBK-217, led by the Naval Surface Warfare Center (NSWC) in Crane, IN, was organized into two phases. First, a Revision G was developed to provide modifications to the existing models but no new models or modeling methods. The second phase will develop further revisions and include advanced methods such as physics of failure methods. Many of the same people worked on both VITA 51.1 and MIL-HDBK-217 Rev G. All the data collected and used for VITA 51.1 was provided to the MIL-HDBK-217 revision working group as a starting point, but there was further development of the modification factors using new data. 

What is the basis of “Quality level of PiQ=0.1” for Rule 2.1.4-2 of the ANSI/VITA 51.1-2008 (R2013) Reliability Prediction MIL-HDBK-217 Subsidiary Specification? The “used Pi Q” was a value used to adjust a MIL-HDBK-217FN2 prediction to match it with a failure rate derived from the field failure. It was not derived, or gotten from some other source. It was a value that was found to fit the observations. The problem is that the match was not exact, and this has caused confusion in the past in trying to duplicate what was done. Generally, a conservative value was picked, and the committee tried not to deviate too far from the original MIL-HDBK-217FN2 handbook.