First Edition Dated September, 2000 33
the engineering specifications. Examples of comparable process capability
indexes include Cpm, quality costs/loss and Z-scores (as used in Six Sigma
programs).
The objective is to measure and reduce common cause variation in the
process so the process produces output close to target with minimum
variation.
See D1-9000-1, AQS Tools, Process Capability Analysis for further
information regarding capability indexes and their calculation.
If attribute data is used, then capability is measured in terms of the defects
per million opportunities (DPMO). To meet an equivalent Cpk of 1.33, the
maximum DPMO is 66.
The key characteristic should be in statistical control before establishing the
process capability. Otherwise, the process capability itself tends to be
unstable.
Process capability indexes should be recorded on the AQS Control Plan (or
equivalent) or in a process capability database. They should be available to
Engineering at both the supplier and Boeing for designing new products and
manufacturing processes.
