1. Design / Process Failure Mode and Effect Analysis (D/PFMEA)
Presented by: Andy Peters on Behalf of Smiths Aerospace

2. Aim of this session To show how to do an FMEA
To show current best practice
To show how to gain benefit from the tool

3. Why do an FMEA You can DESIGN out the failures before they happen
You can control the process and thus process out failures
Reduce rejects – minimise the risk of occurrence
Take this case in particular

4. FMEA Case study DC10 Cargo Door Reproduced from a paper issued by NASA March 21 2005
In 1969 per FAA requirements, Douglas, manufacturer of the DC-10 asked Convair to perform a FMEA of the DC-10 cargo door system
The FMEA discovered 9 sequences that could potentially threaten life. 4 involved sudden depressurisation in flight
1 of the 4 was failure of the locking pin system causing the door lock not to latch, the door could fly open in flight causing sudden depressurisation and possible structural failure of the floor and damage to the tail

5. Smoke and mirrors
The draft FMEA was MODIFIED by Douglas to minimize the design deficiency
A ground test failure in May 1970 was blamed on human error. In retrospect, poor design was downplayed as a root cause
During November 1970 memos between Convair and Douglas discussed proposed fixes to the cargo door problem but NONE were implemented
The FAA certified the DC-10 on July 29, 1971 with an unsolved design deficiency

6. From bad to worse and the smoke thickens
June 12, 1972 the cargo door of an American airlines DC-10 in flight from Los Angeles to New York burst open at 11,500 feet due to the locking pin failing. This resulted in a sudden depressurization. No fatalities at this point
NTSB investigation resulted in a draft FAA order to ground all DC-10s until the design mod was in place
In an infamous “Midnight Gentlemen’s Agreement” the President of Douglas convinced the FAA Administrator not to ground the DC-10

7. The Accident
March a Turkish Airline DC-10 crashed in France killing all 346 people aboard. The cause was faulty latches on the cargo door. Which at 11,500 feet the pressure difference forced the door to swing open to the outside where it was ripped off by the air stream.
After this accident, the entire DC-10 fleet was finally grounded and the cargo door locking system was redesigned and the problem eliminated

8. Lessons learned
A safety analysis is no better than the system we have in place to deal with it
A test failure that does not go to root cause is a missed opportunity to prevent future mishaps
A close call should be treated as an opportunity to prevent a mishap
Risk management is about mitigating risks while their probability of occurrence is still less than 1
“Destination Disaster” a book by Paul Eddy, details the events of this major accident

9. What is an FMEA Analytical tool for risk mitigation
Risk prioritisation method
Method of linking multiple causes and effects to one failure mode
Structured
Widely used in both automotive and other major engineering industries
Widely poorly used
A live document

10. Process Failure Mode Analysis
What are the effects ?
How bad is it ?
What can be done?
Design changes
Process changes
Special controls
Change to standards, procedures or guides
What are the functions
How often does it happen
What are the cause(s)
What can go wrong?
No function
Partial function
Intermittent function
Unintended function
How good is this method of finding it
How can this be found?

11. What does it all mean Function / Item Potential Failure Mode Effect
What is it and what does it do?
Potential Failure Mode
What could go wrong
Effect
What is the knock of impact of the failure
Cause
What could of made this happen
Severity
How bad is this failure to both the customer and the production process
Occurrence
How often could this happen
Detection
What is the odds that the current control will find it
Current control
How do you look for this at the moment, if at all. Both prevention and detection.
Prevention – Poka Yoke, fool proofing,
Detection – Gauging, measurement, spc etc

12. Severity

13. Occurrence

14. Detection Inspection types:
A: Error Proofed – B: Gauging – C: Manual / Visual Inspection

15. Special Characteristics
Significant and critical characteristics can be identified from this
These are as shown.

16. Critical Characteristics
Critical Characteristics are those product requirements that affect compliance with government regulation or safe product operation and which require special actions / controls.
Product or process requirements can include dimension, specification, tests, processes, assembly sequences, tooling, joints, torques, welds, attachments, component usage etc.
Special actions / controls can include manufacturing, assembly, supplier, shipping, monitoring and or inspection actions / controls

17. Significant Characteristics
These are those product, and / or test requirements which are important for customer satisfaction and for which quality planning actions must be summarised in the control plan

18. So How Do We Know Which is Which?
Design
Critical
Severity of 9 or 10 = PFMEA mandated
Significant
Severity of 5 to 8 and Occurrence of 4 to 10 = PFMEA mandated
Process
Severity of 9 or 10. Control is mandated / look at design in the long term
Severity of 5 to 8 and Occurrence of 4 to 10 = Control is mandated

19. Severity * Occurrence Vs RPN
One of the common misconceptions is that the RPN (S*O*D) being greater than a set number is the way to sort the corrective actions out is wrong. (so current best practice tells us)
The trick is to sort initially by S*O (criticality) then S*O*D

20. Corrective Action
If the severity is > = 9 then corrective action is mandatory
If Severity is >=5 and <9 and Occ is >=4 then corrective action is mandatory
There is no trigger level for an RPN number – that is up to you.

21. Responsibility & Target date
Who is responsible to make sure the actions have been done
When is it due to be finished
This shows that just saying that you are going to do something is not good enough. This is a live document and needs to be followed up.

22. Assumptions DFMEA PFMEA
The item is manufactured / assembled within engineering specifications
That the design may include a deficiency that may cause unacceptable variation (i.e. miss builds, errors) in the manufacturing assembly
PFMEA
The design is right
The parts are supplied correctly
That all staff are trained
That no one is wilfully doing it wrong – you can’t control for Muppets!