ABSTRACT
Mean time between failures (MTBFs) can be derived from field data. The number of units in use in the field can be multiplied by the best estimate of the number of running hours for the average unit to accumulate unit operating hours. The number of units in the field is easy to determine from the shipping log. PT-3 can be used to convert field data into MTBF verification charts. Cumulative running hours divided by the expected values associated with cumulative failures generates more and more confidence as the database becomes larger. Charting cumulative MTBF data can alert management to any change of MTBF due to material, workmanship, or premature wearout. MTBF data based on actual run and failure data can be used predict the personnel and facilities needed to support the field service effort. Most field engineers refer to a failure as “a critical incident,” since modern terminology seems to steer away from words like failure or defect.
