FMEA Ranking CriteriaQuick Reference Guide

Detection (DET) Ranking Criteria

Criteria Rating% of failures

being detectedA remote likelihood that the component would be passed on to the next customer containing the defect. The defect is an obvious characteristic that can be readily found.

1 99.99

A low likelihood that the component would be passed on to the customer with the defect. The defect is an obvious characteristic that can be readily detected by a subsequent operation (eg. Missing location hole found during assembly)

2345

95908580

A moderate likelihood that the product will be shipped containing this defect. The defect is an easily identified characteristic examined by inspection checks. Low chances that the current controls will detect the failure mode.

678

757065

A high likelihood that the component will be shipped containing this defect. Practically no chance that the current controls will detect the failure mode.

9 60

The part will be shipped with the defect as no known controls are in existence for detecting the failure mode.

10 Nil

Occurrence (OCC) Ranking Criteria

Criteria RatingProcess Cpk

(if known)Remote probability of occurrence. Process in control and capable. 1 > 1.3

Low probability of occurrence. Process in statistical control and capable although any increase in variation or process shift could cause problems.

2345

1.251.201.101.00

Moderate probability of occurrence. Generally associated with processes that have experienced occasional failures, but not in major proportions. Process in statistical control, but is not quite capable.

6 0.95

High probability of occurrence. Generally associated with processes that have often failed. Process in statistical control but not capable.

78

0.850.75

Very high probability of occurrence. In the team’s view, this failure mode is almost certainly certain to occur. Process out of control and not capable.

910

0.65< 0.55

Severity (SEV) Ranking CriteriaCriteria Rating

The minor nature of this type of failure would not have a noticeable effect on the next higher level assembly or overall engine performance. The customer will probably not be able to detect variation in the product. 1Variation causes only slight customer annoyance. Customer will probably notice only very minor performance degradation, or minor problems at next higher assembly.

23

Customer is likely to be annoyed by the variation in the component. For example, moderate ratings would be given to undesirable attributes such as part adjustment on installation, high forces used in installing the part or visual defects.

456

There will be a high degree of customer dissatisfaction due to the nature of the failure, such as inoperable sub-assembly requiring strip and rebuild. The defect has a severe affect on engine performance.

78

Variation in component feature has a major impact in that it involves potential safety considerations such as in-flight failures leading to loss of engine function.

910