AQL Inspection Manual

Switching Procedures

Normal inspection will be used at the start of inspection unless otherwise directed by the responsible authority. Once Normal, Tightened or Reduced inspection has been executed, it shall continue unchanged for each class of defects or defectives on successive lots or batches except where the switching procedures given below require a change. The switching procedures shall be applied to each class of defects or defectives independently.

Normal to Tightened

When normal inspection is in effect, tightened inspection shall be instituted when 2 out of 5 (or fewer) consecutive lots or batches have been non-acceptable on original inspection (i.e., ignoring resubmitted lots or batches for this procedure).

Tightened to Normal

When tightened inspection is in effect, normal inspection shall be instituted when 5 consecutive lots or batches have been considered acceptable on original inspection.

Normal to Reduced

When normal inspection is in effect, reduced inspection shall be instituted providing that all of the following conditions are satisfied:

ANSI Version

1. The preceding 10 lots or batches (or more, as indicated by the note to Limit Number for Reduced Inspection on the inside of the back cover) have been on normal inspection and none has been rejected on original inspection; and

2. The total number of defectives (or defects) in the samples from the preceding 10 lots or batches (or such other number as was used for condition "a" above) is equal to or less that the applicable number given in Table VIII, Page 16. If double or multiple sampling is in use, all samples inspected should be included, not "first" samples only; and

3. Production is at a steady rate; and

4. Reduced inspection is considered desirable by the responsible authority.

ISO Version

1. The current value of the switching score (see following) is at least 30; and

2. Production is at a steady rate; and

3. Reduced inspection is considered desirable by the responsible authority.

Switching Score

The calculation of the switching score shall be initiated at the start of normal inspection unless otherwise specified by the responsible authority.

The switching score shall be set at zero at the start and updated following the inspection of each subsequent lot on original normal inspection.

1. Single sampling plans:
   1. when the acceptance number is 2 or more, add 3 to the switching score if the lot would have been accepted if the AQL had been one step tighter; otherwise reset the switching score to zero;
   2. when the acceptance number is 0 or 1, add 2 to the switching score if the lot is accepted; otherwise reset the switching score to zero.
2. Double sampling plans:
   1. when a double sampling plan is used, add 3 to the switching score if the lot is accepted after the first sample; otherwise reset the switching score to zero;

Reduced to Normal

When reduced inspection is in effect, normal inspection shall be instituted if any of the following occur on original inspection:

1. A lot or batch is rejected; or

2. (ANSI Version Only) The defect level falls between the Acceptance and Rejection numbers. The lot or batch will be considered acceptable. Normal inspection will be reinstated starting with the next lot or batch.

3. Production becomes irregular or delayed; or

4. Other conditions warrant that normal inspection shall be instituted.

Discontinuation of Inspection

ANSI/ASQ Z1.4-2003 and ISO 2859-1

If the cumulative number of lots not accepted in a sequence of consecutive lots on original tightened inspection reaches 5, the acceptance procedures of this part of ISO 2859 shall not be resumed until action has been taken by the supplier to improve the quality of the submitted product or service, and the responsible authority has agreed that this action is likely to be effective. Tightened inspection shall then be used.

MIL-STD-105E

In the event that 10 consecutive lots or batches remain on tightened inspection (or such other number as may be designated by the responsible authority) inspection under the provisions of this document should be discontinued pending action to improve the quality of submitted material.

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