Boeing first began production of the 777 in 1993 and it continues today in Everett, Washington. An excellent example of root cause analysis and corrective action based on Six Sigma discipline comes from an interesting series of defects found during production in 2005.
An issue became apparent when there were multiple instances of the rejection of recirculating air fans during testing.
A cross-functional Six Sigma team was assembled which included employees from various departments including Engineering, Quality, Manufacturing, and others. The team used DMAIC (Define, Measure, Analyze, Improve, Control) as a framework and employed various root cause analyses until they identified the true root cause. They then put various corrective actions in place along with a plan to monitor results.
The initial finding was a “direct cause” of the problem, which was that debris was entering the fan system and causing damage. They had to investigate deeper (5 Whys, etc.) to find a root cause. Where was the debris coming from and how was it getting into the system?
The team determined that the debris was coming from, interestingly, materials that were put in place specifically to keep debris out during production such as caps and plastic sheeting. These items were not being removed before testing, causing the powerful flow of air to draw them into the fan system causing damage. Some of the corrective actions which were put in place were:
- Adding red streamers to incomplete air-duct installations to make them easily identifiable to testers so fans would not be tested prematurely
- Functional Test work instructions were modified to include a check of the duct system before fans were operated
When corrective actions are put in place it is important to properly implement them including:
- Proper socialization and sign-off of process changes to ensure there is no negative impact to downstream processes
- Communicating the changes to the process, training employees, ensuring all relevant departments, shifts, etc. are made aware of the change
- Designing a monitoring plan to ensure the changes take effect and permanently become part of the process
Read the full case study at boeing.com.