MIL-DTL-0060944B (AR)
s = √ n Σ x2-( Σ x)2/n(n-1)
Other approved standard deviation formulas may be used.
6.8 Critical Inspection Equipment.
6.8.1 System Reliability. The contractor should provide for each defect identified as critical, a
manufacturing and inspection system that assures no more than one in a million contain the defect.
This should be assured by controlling the maximum defect rate produced and the error rate of the
inspection equipment such that the product of the two terms is less than one in a million.
6.8.2 Maximum defect rate produced. The maximum defect rate produced should be defined
as the largest defect rate expected for the characteristic of concern on a monthly or lot basis. The
contractor should establish the maximum defect rate, however, it may not exceed one percent without
approval of the procuring contracting officer. Once established, the contractor should monitor the
defect rate to assure it does not exceed the maximum rate allotted. If the established maximum defect
rate is exceeded, the production of that feature should be terminated until the cause is determined and
corrected. Additionally, all products for that period of time should be rejected and re-inspected.
6.8.3 Maximum error rate of the inspection system. The error rate of the inspection equipment
should be defined as the expected ratio of the number of defective parts accepted to the number of
defective parts inspected by the equipment. The contractor, to meet the system reliability as defined
in 6.8.1, defines the maximum error rate allowed. However, it may not exceed 1/500 without
approval of the procuring contracting officer. Based on the maximum error rate defined for the
equipment, the contractor should develop a demonstration test procedure to demonstrate the error rate
of the equipment. The test should be performed using defective parts or reject standards. No part or
standard should be accepted during the test. If a part or standard is accepted, the cause for failure
should be isolated and corrected and the test rerun. Unless otherwise specified in the detailed item
specification, the minimum number of test samples to be run should be equal to 0.7 divided by the
error rate (e.g. If the required error rate is 1/1000, the sample size would be 0.7 divided by (1/1000) =
700.)
6.8.4 Periodic verification. Periodic verification of the system error rate should be performed.
6.8.5 Redundant inspection equipment. The contractor may elect to use redundant inspection
equipment in lieu of using a single piece of equipment with a very low error rate. Where redundant
equipment is used, the inspection system error rate is defined as the error rates of the multiple pieces
of equipment multiplied together.
6.8.6 Automated acceptance inspection equipment. Equipment for which no, or minimal,
human involvement is required in the acceptance determination. This would include equipment
employing probes/sensors/transducers that are automatically manipulated to perform measuring and
detection functions. If readout is provided, the equipment will be categorized as automated even if
operator interpretation is needed in the accept/reject decision.
6.9 Definitions.
6.9.1 Reliability. The number of successes (rounds chambered, fired, and ejected) divided by
the number tested. Occasionally the last round of a continuous belt, due to the light weight of the
cartridge case, will not fully eject from the weapon. This type of failure should not be classified as a
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