Dealing adequately with technical uncertainties

Statistics, RAMS & Quality Management
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MTBF calculation with MIL-HDBK-217
  MTBF-Calculation acc. to Standards
  Telcordia SR-332
  Siemens SN 29500
  FIDES 2009
  GJB/Z 299C

Mil-HDBK-217 was the first electronic reliability prediction standard and is still the most popular of all current electronic reliability prediction standards. Its initial revision dates back to the early 1980s, and its latest revision F, notice 2 was issued in 1995.
Among all electronic reliability standards, Mil-HDBK-217 has still the best component coverage, which makes it a versatile all-rounder.

As of 2015, updates are not planned. Taking into account that reliability prediction standards are based upon field failure data collected over many years, we can conclude that Mil-HDBK-217F notice 2 reflects the electronic status quo of the late 1980s.

It is obvious that using the Mil-HDBK-217F notice 2 in its original manner would yield results that don't have any reasonable relationship with today's electronics.
Despite the RoHS directive, today's commercial electronic components are beyond any doubt more reliable than military grade components have been in the 1990s.
This problem has been addressed by a consortium of military and aviation companies by developing the ANSI/VITA 51.1 in 2008.

ANSI/VITA 51.1 can be perceived as an add-on for the Mil-HDBK-217.
Members of the ANSI/VITA 51.1 consortium were Boeing, Northrop Grumman, GE, Honeywell, just to mention a few, as well as former Relexsoftware company, whose reliability software suite Relex has been taken over by PTC and renamed into Windchill Quality Solutions in 2010.

ANSI/VITA 51.1 contains recommendations for quality factor assessment for today's commercial electronic components. By applying ANSI/VITA 51.1, Mil-HDBK-217 results on component level would improve by a factor between 1 (switches, connectors, quartz, fuse) and 100 (birdseed like R and C), depending on the component type. On PCB level, results would improve by a factor of 3 to 5, which is still pessimistic. 
Improvement factor = 1 means no improvement at all. For whatever reason, the consortion has recommended that  for switches and connectors, quality factors shall be assessed in the original Mil-HDBK-217 manner, and for fuses and quartzes, there is no recommendation at all.
As a result, switches and connectors have become the key contributors in MTBF calculations if the ANSI/VITA 51.1 recommendations are strictly followed.

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