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H-46 critical chain master scheduling appears to be pro­ceeding as planned with a trend of improving through­put performance. The first aircraft initiated and completed under CCPM was completed in approxi­mately 130 days, as contrasted with an average recent experience of 190 days under the old planning approach. The trend suggests a continuous improvement in turn­around times with a goal of 90 days. The depot now inputs separate aircraft into the CCPM software tool, then combines multiple aircraft into multi-project net­works with multi-chaining in the CCPM software, uti­lizing the critical chain methodology for both induction and process planning, and create a multi-item network of events in desired order of priority sequence. As a re­sult of lessons learned during implementation, they have restricted the number of aircraft in the flow from an average of 22 to 14. The reduction in work-in-process inventory has resulted in lead time reduction and in­creased overall throughput.


Although some organizations have tried it, it appears to be too complex to reasonably use CCPM without com­puter and CCPM software in a complex master schedul­ing environment. There are too many calculations to be performed across all items to create a multi-project criti­cal chain and then update the entire network in a reason­able timeframe. Experience suggests that the multi-project critical chain does not have to be recalculated very fre­quently, but rather sticking to die priorities already es­tablished is more important as variation in actual time to perform tasks occurs. Obviously there are emergency exceptions to this, but every effort is made to eliminate constantly changing priorities where it is not necessary.

This project's results continue to be measured in observed reduction in turnaround time and reduced operational costs related to more effective plan execu­tion as a result of improved resource identification, ac­quisition, and usage. These metrics are easily measured with existing reporting systems. There is a trend toward the lessened need for overtime, and particularly unan­ticipated overtime, which has always been a sore point for workers and supervisors alike. Total repair lead time is trending in a downward direction. Reducing lead time for repair will result in fewer aircraft required in the re­pair pipeline at any one time and result in an increase in operationally available aircraft, possibly offsetting the need for additional asset purchases.

The implementation of critical chain for master sched­uling challenges whatever standards, bills of material structures, and routers exist. It takes a leap of faith to redetermine task durations based on an expectation of missing it 50 percent of the time, until you consider that the other 50 percent is placed in a buffer and available if really necessary. This is a philosophical twist to traditional standards-setting and the process by which they are de­termined. It is very likely that groupings of tasks may be restructured and modified as processes are improved and regrouped and unnecessary delays are eliminated. A change in the way bills of material and routings are de­veloped and how their completion is controlled and re­ported is likely to change in a CCPM environment. Standards and their related costs may decline significantly as the process is viewed differently and multitasking is­sues related to more than one item in repair are resolved in the upfront master planning phase. Cultural resistance to this new way should not be underestimated.


CCPM is emerging as a tool for the master scheduling of multiple items, especially where individually planned items tend to trip over each other to use the same re­sources (materials, equipment, and work skills). In many companies using MRP II/ERP, the master scheduler performs die initial master scheduling somewhat manu­ally. CCPM can provide a real boost for these organiza­tions. The question becomes what to do after the schedule is constructed and input to the MRP logic pro­cessor. MRP may try to reschedule sequences of opera­tions and time phasing as feedback is received. Several potential approaches are suggested:

1.        Use the CCPM tool for planning and scheduling and
use MRP only for material acquisition. The rest of
the MRP II/ERP system can still be used to collect
costs and communicate information throughout the
central nervous system of the organization for inte­
grated resource functions.

2.        Seek an advanced planning system (APS) solution
that incorporates CCPM logic and integrates with
your MRP II/ERP system to provide ongoing dynamic
updates of die master schedule.

3.        Use the CCPM tool for initial master plan develop­
ment, input to MRP, and then allow MRP to manage
beyond that point with occasional sanity checks by
replanning through the CCPM software.

At this point, both options 1 and 2 appear to be the likely candidates, with a thought preference for option 2 for the depot environment. APS with CCPM logic is currently being explored for inclusion in ERP implemen­tation within NADEPs like Cherry Point.

The H-46 Team has now embraced the critical chain master scheduling template as their own and are rec­ommending continuing changes. Some reflect actual man-hour corrections due to having an accurate work history, some recombinations of tasks are being sug­gested because they make good sense, and some add­ing of a few smaller tasks for clarity of explanations is occurring. The depot is having a good exchange in cap­turing real-world hours without extending the turn­around time (TAT). The workers are beginning to actually believe that lower TAT is possible. The man­ager of H-46 repair operations has identified the 10 top parts constraints. These are being tackled one at a time. Using TOC tools and the philosophy, they then present their findings. The shop personnel are seeing exactly how they fit into the CCPM and the impact they have on the sell date of the A/C. They then directly report their progress and constantly see the big pic­ture as to what the next task and priority is. As the backlog of aircraft in the repair cycle becomes smaller, the reduction in cycle time allows them to start deliv­ering in a timelier manner. The necessaty changes that they are implementing in order to achieve these im­provements are transparent to their customers. Now they clearly understand and see that driving the turn­around times down significantly improves their cost basis. This in turn makes their rates more competitive, which in an era of uncertainty is the key to survival. Now there is real management help being provided to solve workers' problems (constraints) as they surface as rocks in a stream. As one manager recently com­mented, "It is fun to watch the expression on people's faces when they are told they need to improve their processes because the A/C are now selling 40 days faster. I tell them that this is the good news and that the A/C line is continuously improving and so must we. This is more about working smarter than working harder."

For balance of this article, click on the below link:

Lean Manufacturing Articles and click on Series 12

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