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An interesting program used by some airlines, that is not widely trumpeted involves Ship or Shelve (SOS) procedures. It is my belief that this is not heralded because, to the degree it is properly executed, it will provide a competitive advantage. Although operators may call this type of program by differing terminologies, it essentially involves screening selected parts to see if their removal and replacement actually fixed a reported aircraft writeup, and if not, returning that part to stock.

Here’s a simple yet realistic example: A pilot reports that the “Autopilot disengaged in flight.” The technicians replace the autopilot processor. On the next flight the crew reports the same writeup. Technicians then replace the autopilot reference gyro. The aircraft flies 5 more flights without any reports of the autopilot disengaging. It seems conclusive that the replacement of the gyro, not the processor, fixed the writeup. Now, what do you do with the processor? It costs $5,000.00 dollars just to check it at your MRO supplier, for what will certainly be a No-Trouble-Found determination. BUT, if the processor is on your Ship Or Shelve program, you return it to service (put it on the shelf as a spare instead of shipping it to your MRO supplier). What are the advantages of such programs?

• The airline saves the No-Trouble-Found charges
• The airline saves the part from being in the MRO supplier’s Turn Around Time (TAT) cycle. For example, your supplier has a 30 day TAT, but your SOS program has a 3 day TAT (an affirmative smile and wink please).
• A successful SOS program may lead you to conclude you have too many spares for the given part (endearing you to your CFO who will expect you to lower your inventory).

Maintenance fundamentalists may at first express some disharmony with this practice, but as would be expected, this type of program requires solid processes and procedures, and close monitoring and reporting to establish its effectiveness. With today’s programmed automation, the monitoring and reporting would not be as burdensome as thought. The processes and procedures would be expected to be contained in an airline’s General Maintenance Manual or General Procedures Manual. What are the critical guidelines and considerations for a successful program?

• The initial candidates for this program should be those with high rates of Unconfirmed Removals, or those with high rates of No-Trouble-Found. When formulated with the costs your MRO supplier is charging you for these, you should be able to quickly identify your top ten list
• Establish a segregated area for the parts to be stored while being evaluated, and give the area a unique numbered location, bin, or shelf area so that anyone querying your system will know some parts are in the SOS cage.
• Establish a training program in order to authorize only certain employees to evaluate the parts and to return them to service
• Establish a base line period in which each SOS evaluation will be performed. For example, the part was just removed, placed in the SOS cage, and now your system monitors the aircraft it was removed from for additional writeups. How many flights are you going to wait for to see if there were repeat writeups? I’d use the fleet stage length as a gauge. For example, if you had small stage lengths of 2 hour flights, consider 4-8 flights. Conversely if you have long stage lengths of 12 hours, consider 2-4 flights. This should also be tempered by the speed with which writeups are entered into your maintenance tracking computer system. It is this system that your SOS evaluator will be monitoring for repeat writeups, so if it takes 24 hours on average to assure writeups are entered into your system, then the “Flight Clock” starts 24 hours after the removal. Regardless, do what you feel comfortable with.
• Develop reports such as:

• SOS Turn Around Time
• Volume shipped versus volume shelved
• The writeup confirmation rate, or trouble-found rate at your MRO supplier should rise for the selected SOS parts; do you have reports to confirm it?
• Your existing programs/reports for detecting and identifying chronic or rogue aircraft and components (see my blog on Chronic and Rogue parts) should dovetail with the SOS program. That will take a little thought.

• Documentation: Of course your maintenance documentation must have a clear audit trail; for a given serial numbered part, anyone must be able to observe how many times a part was repaired, overhauled, or returned to service by your SOS program, etc. Likewise, when returning a part to service via the SOS program, your tags or forms should contain standard language apprising anyone of the fact.

Royboy’s counsel: Training and procedures should be tailored to the conservative side of evaluations. For example, lets use that autopilot scenario again. Lets say we agree that the gyro, not the processor was culprit. You’re getting ready to return the processor to service, but notice that it is marked ESD sensitive, and the part was brought to the SOS cage from the aircraft without ESD protective caps on the connectors. Can you assure that no one has introduced ESD damage since it was removed from the aircraft? Send it to your MRO shop. Another one: The original pilot writeup was “Autopilot disengaged in flight.” The processor was replaced, but on the next flight a different crew writes “Yaw channel disengaged in flight.” Was that the same writeup written a different way? Now the skill, training, and background of your authorized SOS evaluator comes into play. Not sure? Send it to your MRO shop.

Finally, uneasy maintenance fundamentalists should keep in mind the following: Using the Autopilot example, remember that processor that was returned to stock by the SOS Program? Upon installation the next time, it will have to pass all the functional checks required by the maintenance manual for a removed and replaced part, BITE checks etc.

I’m disengaging...retard the throttles.

8/23/06

Roy Resto - VP Technical Operations, FAA-DAR
Phone: 414 875-2191   Fax: 414 875-0200
royboy@mbtrepair.com

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