The Role of Process Failure Mode and Effects Analysis (PFMEA) in Aviation System Root Cause Analysis

Sofema Online considers the role of Process Failure Mode and Effects Analysis (PFMEA) in Aviation System Root Cause Analysis.

Introduction

Human and System errors can have quite significant negative outcomes. Process Failure Mode and Effects Analysis (PFMEA) looks at each process step to identify risks and possible errors from many different sources.

The sources most often considered are:

○ Human
○ Process
○ Material
○ Tooling Equipment & Machinery
○ Measurement
○ Environment
 

Steps to Conduct a PFMEA

1/ Review the entire process - Use a process flowchart to identify each process component;
Brainstorm potential failure modes.

2/ Review existing documentation and data for evidences.

3/ List potential effects of failure
Note - There may be more than one for each failure.

The effects of a failure are focused on impacts to the processes, subsequent operations and possibly customer impact. Many effects could be possible for any one failure mode. All effects should appear in the same cell next to the corresponding failure mode.

Failure Mode - are the anti-functions or requirements not being met. There are 5 types of Failure Modes:

a) Full Failure
b) Partial Failure
c) Intermittent Failure
d) Degraded Failure
e) Unintentional Failure

4/ Determine & Assign Severity rankings - Based on the severity of the consequences of failure

Severity: 1 = Not Severe, 10 = Very Severe

Typical Severity for Process Effects (when no Special Characteristics/design inputs are given) is as follows:

○ 2-4: Minor Disruption with rework/adjustment in stations; slows down production (does not describe a lean operation)
○ 5-6: Minor disruption with rework out of station; additional operations required (does not describe a lean operation)
○ 7-8: Major disruption, rework and/or scrap is produced; may shutdown lines at customer or internally within the organization
○ 9-10: Regulatory and safety of the station is a concern; machine/tool damage or unsafe work conditions

5/ Assign Occurrence rankings - Based on how frequently the cause of the failure is likely to occur:

Occurrence: 1 = Not Likely, 10 = Very Likely

6/ Assign Detection rankings - Based on the chances the failure will be detected prior to the customer finding it:

Detection: 1 = Easy to Detect, 10 = Not easy to Detect

Typical Process Detection Ratings:

○ 1: Error (Cause) has been fully prevented and cannot occur
○ 2: Error Detection in-station, will not allow a nonconforming product to be made
○ 3: Failure Detection in-station, will not allow nonconforming product to pass
○ 4: Failure Detection out of station, will not leave plant / pass through to customer
○ 5-6: Variables gage, attribute gages, control charts, etc., requires operator to complete the activity
○ 7-8: Visual, tactile or audible inspection
○ 9: Lot sample by inspection personnel
○ 10: No Controls

7/ Calculate the Risk Priority Number  RPN - Severity X Occurrence X Detection

8/ Develop the action plan - Define who will do what by when

9/ Take action - Implement the improvements identified by your PFMEA team

10/ Calculate the resulting RPN - Re-evaluate each of the potential failures once improvements have been made and determine the impact of the improvements

Sofema Aviation Services and Sofema Online provide EASA Compliant Regulatory & Vocational Training including Quality & Safety Assurance and Root Cause Analysis Techniques.
Please see the websites or email: office@sassofia.com or online@sassofia.com