It is hard to imagine that an evolution from proven efficiency-improving concepts of Lean and Six Sigma could drive even more throughput for an organisation the size of Delta TechOps. But the application of Eliyahu Goldratt's "Theory of Constraints" is underpinning the drive of Delta's maintenance business to reduce the time engines spend in overhaul by up to 50%.
Goldratt, an Israeli physicist turned management guru, introduced the Theory of Constraints with his 1984 book The Goal. At its most basic level the concept is a management approach focused on identifying and relaxing constraints or bottlenecks that hamper an organisation's efforts to get closer and closer to fully attaining its performance objectives. It builds on the Lean philosophy of eliminating waste to cut costs and decrease production time.
© Delta TechOps
"We've learned new tools that we didn't even have with Lean," says Delta TechOps president Tony Charaf.
Building on concepts of Six Sigma and Lean, which Delta TechOps adopted from 1997, the Theory of Constraints was introduced in late 2005 and early 2006. Charaf stresses the concept has served as the anchor of Delta's engine cycle time reduction.
Overhaul throughput for Delta-operated engines has risen to 50-58 a month from 30-40 before applying constraints theory, says landing gear product line manager John Clark. As the application evolves over the next couple of years, Clark estimates Delta's maintenance unit could increase overhaul capacity to an annual run rate of 800, from 650 this year.
Turnaround times for Pratt & Whitney JT8D 219 engines have already fallen from 50 days to about 20; turnaround times for PW2037s are about 24 days.
A large portion of applying the constraints theory at Delta TechOps is the focus on refining the flow of engine components cycling through the overhaul process after engine teardown.
Using the Theory of Constraints, Clark says that Delta significantly cut the amount of parts in the rework process from around 20,000 to 5,500.
Charaf says the theory has not reached full maturity at Delta TechOps. "We'll probably go another year or so and then we will raise the bar one more time. But that's how we've been approaching continuous improvement.
"You cannot go from doing no continuous improvement, and then become a master at it through Theory of Constraints, you just cannot do that."
The organisation is also working on other process improvement projects. Charaf is pushing for a deeper application of Lean, and also to manage suppliers "at a much closer range".
Charaf says: "In the past you used to strike deals with suppliers on cycle time. If you want to overhaul a fuel control they come in and they quote a 30-day cycle time. We're not doing those deals any more.
"We have really departed from them holding us hostage based on cycle time and us increasing our inventory to get the job done."
Instead, Delta TechOps is giving suppliers specific deadlines for parts delivery. For example, Charaf says, suppliers are told: "Every Wednesday at 08:00 I need this fuel control on my deck. What is it that you're going to do to deliver that?"
And, he says, Delta's size following its 2008 merger with Northwest Airlines means most suppliers are coming along with TechOps' shift in parts delivery methods: "Our size now is very leveraging so the people that really want to do business with us, they're on the bandwagon."
The net impact of hammering away at constraints, changing the dynamics of supplier relationships and other initiatives is a significant improvement in overhaul turnaround times. Charaf says that when most of those projects are complete, by early 2011, "our cycle time will be very competitive compared to the industry".