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...


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 maintenance, he has worked the line, shop, maintenance control and component reliability engineering disciplines.

The industry is in trouble, and everybody is focused on cost containment. Grasping for the "low hanging fruit," a number of painful initiatives have been implemented with limited success. However, the lowest hanging, pain-free fruit has typically been overlooked — the rogue unit. Its impact is felt across the entire organization, both for the operator and the repair facility, and it’s huge.
Not only does it affect the direct operating cost, but it also generates a lot of unnecessary studies and initiatives, hamstrings the airline’s operational performance, and demoralizes the front line and repair facility troops.

What is it?
imageA rogue unit is like the proverbial "rogue elephant" in that it is an individual component gone awry. It repeatedly experiences short service periods, manifesting the same system fault every time, and whose replacement resolves the system malfunction. The problem is that when it is sent in for repair, the standard bench or overhaul testing can’t identify its unusual failure mode.

How does it happen?
Bench testing does not address 100 percent of what a component does, where it lives, or how it operates. It’s not intentional, it’s just a fact of life that the shop is not the same as the aircraft. Also, bench tests are designed to identify anticipated failures — checking things that are expected to fail. So a unit that fails in an unaddressed or unanticipated way will never be resolved — a rogue is born.
Any component can become rogue. We’ve even identified a rogue pilot’s seat (the actual aircraft seat itself – not the pilot’s seat!). So it’s important to remember that rogue units aren’t isolated to the "high tech" world.

"Natural selection"
It would be bad enough if rogue units just existed somewhere in the inventory. But there’s a phenomenon that catapults its effect throughout the entire airline’s operation. It’s like a Darwinian "natural selection" thing, just in reverse — survival of the worst, rather than the fittest — in that rogue components will displace serviceable spares.
The way that happens is like this: Let’s say there are four serviceable units in the spare pool. A unit in service fails in a way that starts its rogue career, so it goes to the shop and back to the pool. Now, there are three serviceable spares, and the rogue unit. Over time, there is a good chance another unit in service will develop a rogue failure. It will also make the trip to the shop and back to the spare pool. Now there will be two serviceable spares and two rogue units in stock.
As long as there are no problems with the parts in service, the rogue units will sleep peacefully in the spare pool. But, as soon as there is a problem in service, there’s a 50/50 chance that a spare will be pulled from the pool that has a problem of its own. As bad as that sounds, if the rogue units aren’t identified and resolved, the rogue population will continue to grow, displacing more spares. Think what would happen if all of them became rogue units!

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