Revamping MIL-HDBK-217: Weíre ready for it

The new VITA 51 open standard is adding practical and quantitative reliability prediction recommendations to the military's venerable MIL-HDBK-217.

The military’s venerable MIL-HDBK-217 has been around for more than 40 years; it’s time to add some quantitative and practical recommendations to these reliability predictions with a new open standard called VITA 51.

Failure rate predictions are used on military and high-reliability platform programs for myriad purposes, including reliability analysis, cost trade studies, availability analysis, spares planning, redundancies modeling, scheduled maintenance planning, product warranties, and guarantees. In the 1950s, electronics reliability predictions were first standardized by the Department of Defense (DoD) through the analysis of historical data. This led to the publication of the first edition of MIL-HDBK-217 in 1961, providing the basis of reliability predictions that is still in wide use today.

In 1994, U.S. Secretary of Defense William Perry published his pivotal memorandum titled "Specifications & Standards - A New Way of Doing Business." One consequence of the memo was that military acquisition changed dramatically, and many military standards were cancelled in favor of commercial standards and practices. Another consequence of the memo was that the DoD stopped updating MIL-HDBK-217 and instead looked to industry organizations to provide updated reliability prediction methods.

Accordingly, the working group was formed in 2004 to investigate the state of the reliability prediction industry and develop a method to address electronics failure rate prediction issues. They found that the MIL-HDBK-217 method had become obsolete compared with current electronics technologies; however, it remained the most common method used in industry to predict electronics reliability. Most companies have developed proprietary and unique adjustment factors to MIL-HDBK-217 for their reliability predictions, leading to incomparable and unsubstantiated reliability analyses. This poses a problem for system integrators and customers who no longer have credible or consistent reliability predictions from the supply chain.

The VITA 51 working group addressed this problem by establishing a Community of Practice (CoP) - with representation from suppliers, OEMs, integrators, and the DoD - and developing a series of specifications. The VITA 51 main specification addresses the limitations of existing practices, while a series of subsidiary specifications establishes common practices within the industry for specific reliability prediction methods. The main document also establishes a CoP registration process to ensure that additional companies will contribute to future development of these methods.

Why is VITA 51 needed?

The Naval Surface Warfare Center (NSWC) Crane Division originally proposed the VITA 51 effort and has maintained a leadership role in specifications development. Their stated goal was to achieve consistency of reliability predictions, and to achieve this by consensus among a wide community of practitioners. Together, the working group established a specific collection of modification factors to MIL-HDBK-217. It did not matter if a completely rigorous derivation of these factors was available, so long as the resulting numbers made sense and could be standardized. A later effort could address the deeper issues of more accurate reliability predictions, more thoroughly researched and substantiated modification factors, and updated modeling techniques.

Since 2004, NSWC Crane has maintained an industry survey of reliability prediction methods and practices as illustrated in Figure 1. Their survey seeks information on two key issues. First, how many reliability predictions are based on traceable sources? Second, which prediction methods and tools are used? They have found that, from a survey of 1,900 electronics COTS items, only 437, or less than 25 percent of the items had published and traceable reliability predictions as illustrated in Figure 2. Of those with traceable reliability numbers, a total of 167 or 38 percent were predicted using MIL-HDBK-217.

21
Figure 1

22
Figure 2
(Click graphic to zoom by 1.6x)

Although the handbook has fallen out of currency and its accuracy is questioned by many industry experts, the market continues to choose to use MIL-HDBK-217 for reliability predictions. Additionally, systems integrator companies and military customers continue to expect and accept predictions based on MIL-HDBK-217. There is a clear need for improved reliability predictions, and consequently the VITA 51 working group has had participation and interest from a wide industry community, including non-VITA member companies.

Traveling in good company

The main contributors to the VITA 51 working group have been representatives from Boeing, Curtiss-Wright Controls, the Defense Supply Center Columbus (DSCC), Foxconn, General Dynamics, GE Fanuc, Honeywell, Moog, NSWC Crane, Raytheon, and Relex Software (Figure 3). The working group has been recently joined by participants from Northrop Grumman and Sandia Labs. This broad participation has been critical for the development and acceptance of the specifications. In addition, leadership from the DoD has been critical to keep the work focused on the needs of military and high-reliability applications.

23
Figure 3
(Click graphic to zoom by 1.7x)

The VITA 51 working group's efforts have been monitored by a broader base of industry, including practitioners from 3COM, ATT, Amphenol, Broadreach, Connect Positronic, DDC, Harting, Leach International, VMETRO, Motorola, Texas Instruments, Schroff, Sparta, Sun, and various branches of the DoD. Their interest resulted from presentations that VITA 51 members have made in conferences such as The International Society of Logistics (SOLE) 2005 conference, the 2006, 2007, and 2008 Components for Military and Space Electronics (CMSE), the 2007 Bus&Board Conference, and by invitation at the Government Electronics and Association of America (GEIA) G-12 committee meetings in 2006 and 2007.

In December 2007, NSWC Crane was directed by the Defense Standardization Program Office (DSPO) to initiate an effort to develop and publish a complete revision to MIL-HDBK-217 (to become Revision G). In January 2008, NSWC Crane put out a call for participation and interested parties for this effort. Comments, suggestions, and offers to help may be submitted at: www.crane.navy.mil/sd18/ReliabilityFeedback.htm. They hope to complete work on Revision G by the end of 2009. While this effort may take several years to come to fruition, they have welcomed and supported efforts such as VITA 51 as a much-needed interim solution and first step in the development of a revision to MIL-HDBK-217.

Current status

The VITA 51 specifications are currently going through the ANSI/VITA balloting process. The initial ANSI/VITA ballots passed, but generated substantial industry comments that the working group has used to improve the specifications. The working group plans a recirculation ballot in early 2008.

While specifics of the VITA 51 specifications may change during the ballot process, some significant differences with reliability predictions using the original MIL-HDBK-217F Notice 2 will be seen by anyone using VITA 51. For example, the quality factor for commercial quality integrated circuits, PiQ, is set at 10 in MIL-HDBK-217F Notice 2 and has been changed to 1 in VITA 51. This results in a tenfold improvement in a predicted failure rate for these components. The reason for this change is the observed overall improvement in commercial quality versus military quality components experienced in industry since 1995. Also, for some discrete component technologies, field experience data from participating companies indicated that even the PiQ quality factor of 1 is conservative, but was acceptable by the majority of participating companies.

VITA 51: The best of all worlds

The VITA 51 working group was formed to fulfill a need brought to VITA by the DoD, and the effort has resulted in specifications that address a problem that has developed in the reliability prediction business of consistency in predictions. There has been broad industry interest and help in the development of these specifications. The DoD can now launch a new effort to revise MIL-HDBK-217, and have confidence that it will have industry interest, help, and participation during the development of the next revision and wide acceptance when it is published. VITA 51 has met an industry need, and at the same time provided the military customer with a needed service. CS

Lori Bechtold is a reliability engineer with 23 years' experience with Boeing, spanning programs in military, commercial aviation, and space applications. She is the chair and technical editor for the VITA 51 working group. Lori holds a BS in Mathematics from the Massachusetts Institute of Technology. She can be reached at lori.e.bechtold@boeing.com.


253-657-6131
www.boeing.com