The Fallacy of MTBUR & MTBF as Reliability Metrics

The Fallacy of MTBUR & MTBF as Reliability Metrics

Thomas Carroll

NetJets, Inc October 25, 2005

Thomas Carroll, Director of Reliability Engineering "The Fallacy of MTBUR & MTBF as Reliability Metrics"

Traditional Measurement

? Mean Time Between Unscheduled Removals (MTBUR)

? Mean Time Between Failures (MTBF)

Great for measuring rates of removals or failures, but do they actually indicate reliability?

Thomas Carroll, Director of Reliability Engineering

1

"The Fallacy of MTBUR & MTBF as Reliability Metrics"

How Are They Calculated?

MTBUR = Number of flight hours x units installed per aircraft Number of unscheduled removals during that period

MTBF = Number of flight hours x units installed per aircraft

Number of shop confirmed failures during that period

Thomas Carroll, Director of Reliability Engineering

2

"The Fallacy of MTBUR & MTBF as Reliability Metrics"

What Should a Reliability Measure Do?

?Identify reliability issues

D Premature failures D "End of Life" failures D Rogue components D Shop workscope shortcomings D Scheduled maintenance program problems

Thomas Carroll, Director of Reliability Engineering

3

"The Fallacy of MTBUR & MTBF as Reliability Metrics"

What Does MTBUR NOT Tell Us?

?Reliability issues

D Premature failures D "End of Life" failures D Rogue components D Shop workscope shortcomings D Scheduled maintenance program problems

Thomas Carroll, Director of Reliability Engineering

4

"The Fallacy of MTBUR & MTBF as Reliability Metrics"

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