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Component Reliability - Rogue Parts
Rogue parts are those components that seem to spend more time in the repair shop than they do on an aircraft. The typical rogue part never remains installed on an aircraft for long. The part seems to exhibit the same failure mode regardless of which aircraft it is installed on. Compounding the problem – the repair shop usually cannot duplicate the failure in the shop. The end result is a vicious cycle of aircraft removals and repair shop visits. A true story about a rogue component follows:
An Attitude Deviation Indicator (ADI) had a long history of pilot reports for an intermittent “Runway Flag”. This ADI had been removed from five different aircraft for the same “Runway Flag” problem. After each removal, the instrument repair shop was unable to duplicate any failures with the ADI. A summary of shop actions is as follows:
1. No Fault Found (NFF). Bench tested and returned to service.
2. NFF. Performed visual inspection of runway gear train. No abnormalities noted. Bench tested
and returned to service.
3. NFF. Due to previous history, cleaned and lubricated the rising runway assembly.
Bench tested ad returned to service.
4. NFF. Due to previous history, replaced the runway flag solenoid and adjusted the orientation
of the flag. Bench tested and returned to service.
5. NFF. Due to previous history, replaced the runway/localizer drive circuit card. Bench tested
and returned to service.
Within a few days, the ADI was back in the repair shop for; you guessed it, an intermittent runway flag. To make a long story short, the rising runway and the localizer are part of the same mechanical drive system. After a lengthy evaluation, it was found that the runway symbol was getting caught on a feedback resistor clamp when the localizer was driven all the way to the right. This would cause the runway flag to pop into view. Repositioning the clamp solved the problem.
In this example, the rogue issue occurred because the ADI test procedure only tests the runway system with the localizer in the center position. As we now know, the problem was occurring when the localizer was driven fully to the right. Therefore, the existing test procedure was modified to test the runway drive three times – with the localizer in the right, left and center positions. The new test procedure will guarantee that this failure mode is caught during the first shop visit - never becoming a rogue issue in the future.
The consequences of a rogue part are significant – and can have a tremendous impact on your maintenance organization. Rogue components increase workloads for line and shop technicians. Rogues frequently contribute to flight delays and cancellations. The consequences of the rogue ADI from our example:
A. Six pilot-reported problems that required line maintenance assistance
1. Troubleshooting time
2. Part replacement
3. Paperwork
B. Two flight delays
1. 25-minute flight delay due to heavy line maintenance workload
2. 10-minute flight delay due to delay in part arriving from storeroom.
C. Shipping and Handling of six ADIs
1. Delivery from storeroom to aircraft – back to storeroom
2. Shipping from storeroom to repair shop
3. Shipping from repair shop to storeroom
4. Insurance costs for freight delivery
D. Repair shop costs
1. Technician labor for troubleshooting
2. Technician labor for part replacements, adjustments, tests, etc.
3. Cost of replacement parts that fixed the ADI
4. Cost of parts that did not fix the ADI
5. Paperwork
If you were to assign a dollar value to each of the consequences in this list, the total cost impact as a result of this rogue ADI is well over $10,000 – not to mention the headaches that it caused! That is why it is critical to identify and resolve rogue issues as soon as possible.
Unfortunately, rogue issues are more common than you think. The average sized air carrier usually has somewhere between 300-400 rogue components in its inventory at any given time. These rogue components can be anything from coffee makers to flight computers to Auxiliary Power Units (APUs). Total cost impact due to these rogue issues can be millions of dollars per year.
Every air carrier needs to have a system in place to identify, track and resolve rogue components. An effective program pays for itself after the first few rogue issues are resolved. Every rogue resolution after that is money in the bank! Aviation Reliability Services has extensive experience in identifying, tracking and resolving chronic component issues. We can also help you build business cases to recover costs incurred by ineffective repairs. Most importantly, we can help you work with your repair vendors to eliminate the causes of rogue issues. Contact our Reliability Engineer for more information.
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