Rogue Units: Focus on cost containment

Rogue Units Focus on cost containment By Thomas Carroll October 2001 Thomas Carroll is the Manager of Reliability Engineering at US Airways at Pittsburgh International Airport, Pittsburgh, PA. During his 28 years in aircraft...

The rogue unit effect
imageAs the "Natural Selection" phenomenon continues, the negative effect will be felt throughout the airline operation: Operational and dispatch reliability, aircraft systems, maintenance effectiveness, airline/OEM engineering, maintenance support, training programs, the repair facility, spare levels, component "quarantine" programs, and other components as well.
Here’s what usually happens when a rogue unit is installed in an effort to correct a system malfunction that only manifests itself during flight. The problem continues (since a defective part has been introduced), so the troubleshooting tree directs the replacement of other system parts in succession. Then, bizarre troubleshooting methods are employed as the troubleshooting tree runs out of options and wiring or plumbing is checked and shaken down. As the chronic problem persists, there is also an increase in MEL activity and delays or cancellations. Finally, when logic is thrown out the window, all of the parts are replaced again in the hopes of making the problem just go away. Mercifully and unexplainably, the problem eventually disappears. The rogue units make their trip to the repair facility and back to the spare pool, waiting to do it all over again.
Is maintenance elated that they’ve defeated the chronic problem? Usually they’re just glad that it’s gone away, so there’s noreal victory to improve morale. In fact, the morale typically suffers even more as fingers are pointed and armchair quarterbacking takes place later. Even the repair facility feels frustrated by all the "no fault founds" that are flowing through the shop.
Additionally, the problems generated by the rogue units will appear to be caused by other drivers — design flaws, human factors, training, Built-In Test programs, or a host of other issues, which generate a bunch of fruitless investigations and initiatives.

Rogue impact on MTBUR
While everybody wants to see costs go down, they’d all love to see component MTBUR (Mean Time Between Unscheduled Removals) go up. Of course, all the reliability modifications, training and other initiatives are working to improve the MTBUR, and are typically considered successful if there is an improvement of 10 percent to 20 percent year over year. An effective rogue unit identification and resolution program will do much more than that. As the chart (please see pg. 22) shows of a real-life component, it is possible (and quite probable) to see sustainable improvements of over 100 percent when the rogue units are targeted and resolved.

Then, there’s the direct cost

Chart shows the impact of rogue units on MTBUR.

Any time parts are replaced, it costs money. There is a whole infrastructure built within the maintenance organization to facilitate the movement and tracking of unserviceable units to the shop and refilling the holes on the spare shelf with serviceable ones. Additionally, any time maintenance is performed on the aircraft, there is the direct cost of the technician, along with a host of support equipment required to facilitate the repair and system checkout. Even the system checkout generates a cost, in that the system components are exercised, which shortens their useful lives in service.
So, when considering the typical life of a rogue unit: usually six more installations after becoming a rogue (before some sort of "accident" befalls it); the associated "no fault found" costs; the additional system parts replaced needlessly; their associated "no fault found" costs; and the hours of troubleshooting the system wiring and plumbing unnecessarily; the average cost for each rogue unit comes out to be around $50,000 to the maintenance division. And, this figure doesn’t even represent delays, cancellations and additional inventory impacts!

Is there hope?
In a word, yes. However, it requires the development of a couple of key elements in order to have a good identification and resolution program. The most important element is the tracking of each component by serial number. This would include date on/off, aircraft number, position, reason for removal, time since installed/overhauled, etc. Without this critical information, there is no hope in controlling rogue units.
The next element is a process that identifies the potential rogues as they develop, such as three consecutive installations that are less than 1,000 hours each. Then an assessment must be made to sort out the real rogues from the ones that just appear to be rogue. Over the years, our confirmation rate has hovered around 66 percent, which means the other 34 percent were victims of circumstance rather than bona fide rogue units. Without such a screening process, how would the shop know which 3 units to ignore out of the 10 that appear to be rogue?
Finally, open communication needs to be established between the maintenance operation and the repair facility. Rogue units require new and unique testing to identify and resolve the oddball failure, so the shop needs to understand how and where the unit operates in service in order to mimic those conditions.

Benefit for all
Why go through all this? It’s obvious that there is a big payoff for the operator in cost avoidance. There’s also great incentive for the repair facility to focus on rogue resolution. The OEM’s name is all over their parts, and their reputation is a direct reflection of the component’s performance. Other repair facilities, whether in-house or out, are also resting their reputation on the reliability of their product. Without a doubt, rogue units will cause irreparable damage to a reputation.
Additionally, rogues will not go away. When one odd failure is resolved, another will develop over time. If constant surveillance isn’t maintained, then the rogue population will continue to develop, grow and wreak havoc on an even grander scale.

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