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CAVU Café: Royboy’s Prose & Cons

*Note: The views expressed in CAVU Café: Royboy’s Prose & Cons blog are those solely of the writer and are not necessarily shared by the Aviation Suppliers Association or the Association’s staff, members, or Board of Directors.


   About Roy Resto



A characteristic of human expression which seems to be on the wane is that of passion. You’ll know when a person is passionate about a topic of discussion when: the blood vessels in the neck are seen to bulge, the hand motionsbecome more expressive, and the tone of their voice changes to that level characterized as “don’t dare to interrupt me during my discourse or I’ll wag my finger at you.” That such impassioned expression is on the wane is a casual observation on my behalf, but if true, why? Two guesses would be that 1) We have become fixated on being politically correct and universally un-offensive, and 2) We have become shy and timid; afraid of rejection by counterpoint and what will be thought of us in the process. If you have ever had the opportunity to be involved in addressing issues of chronic or rogue parts for your company, you likely experienced at least lively conversation, if not downright impassioned exchanges.


There are certain parts or components that manifest the same recurring problems or writeups over and over again within a certain period. Such parts or are said to be exhibiting ‘chronic’ or ‘rogue’ histories. Maintenance folks have often called these offenders ‘Hangar Queens’ due to their frequent visits to the shop.



The typical pattern is that initially the shop will return the part to service with a ‘Could not duplicate’, or ‘No trouble found’, or that corrective actions did not eliminate the pesky, recurring writeup. This may occur a few times before the part is declared ‘chronic’ or ‘rogue.’ A simplistic definition for these parts is that they pass all the required Maintenance Manual tests and inspections, but do not last on the aircraft. Most shops or airlines establish a baseline, rule of thumb to make the determination that a part is chronic or rogue; for example, if a certain serial number part exhibits 3 removals in a six month period. These baselines vary widely depending on the family of parts, ATA chapter, and/or the airline or shop policy.



I’ve had the sad experience to hear some end users of these parts express some pretty inflammatory remarks regarding the practices of the maintenance folks who repair these parts. This is sad because this uninformed view does not accommodate the reality that these parts will, and do exist, but until they are identified, the maintainers are doing everything according to the approved data and their training. In fact the maintainers take great pride in their art, and are the first to self-inflict umbrage when they learn that previous attempts to repair a part have failed. The real work and test of the maintainers starts after the part has been identified as chronic or rogue. Myopic critics abound too, on the side of the shops who must fix these units, about the operator’s methods. The uniformed critic needs to ask two questions: What causes this phenomenon, and what is typically done to address it?



The causes of chronic or rogue parts generally fall into these categories

  • Variation: Variation in the manufacturing process: Anyone who has studied statistics in manufacturing will be familiar with the term “Variation.” The Holy Grail in manufacturing is to eliminate such variation in the product. Manufacturers with Six-Sigma processes for example, are said to exhibit the least variation in the product. Regardless, variation exists in any process, and that variation may exhibit itself in a particular serial number that will eventually end up on someone’s chronic list. To be totally honest in this tech log, I’d have to acknowledge that variation exists in the maintenance process as well. A manufacturer may have produced a flawless part, but later during maintenance, a technician may have accomplished a poor solder joint repair or improperly crimped a wire for example. These could lead to intermittent failures.
  • Intermittent Failures: This is the bane of maintainers. These faults seemingly manifest themselves randomly, and of course, rarely in the shop. There are many causes which may include the following: Variation in the manufacturing or maintenance process as previously discussed; undetected wear; corrosion; abuse such as being dropped or mishandled; ESD damage; severe events such as lightning strikes, hard landings, landing gear collapse, or collisions with ground vehicles; coffee, water, lavatory leaks or other spills; failure of other parts in the system such as an over-voltage condition, etc.
  • Software: This is quite specialized, but it does happen. Many parts are controlled by software and interact with other systems similarly controlled by software. Such software is routinely updated, and occasionally the new software causes the system to act in unforeseen ways. This naturally causes the pilots to writeup the system, and the aircraft technicians to take corrective, remove-and-replace actions; of course the shops can find nothing wrong with the units. It may be months before the operator or manufacturer correlates the failures with the new software, and in the meantime, the rogue list has grown significantly.
  • False indicators: Sometimes the problem does not lie with the part, but with the airplane. Do rogue or chronic problems exist on the aircraft side? Of course they do, you silly wabbit. I’ve seen some problems on aircraft that defy troubleshooting logic and whose final fix may not occur until months later. In the mean time multiple removals of the same part may have occurred, and the repair shop is being asked what are they doing about the spikes in removals or chronic lists?


Remember that these parts all pass the tests required by the maintenance manuals, and I’ve never met a manual that had a troubleshooting section that addressed all problems. Fixing it will require a mixture of experience, logic, the process of elimination, and sometimes just plain old dumb luck. For those with experience in the area, the process starts with coming up with a written plan. Here’s a sampling of some common techniques that may be used in the plan.

  • Check all the available data for correlation. For example: Are the parts coming from a single aircraft tail number; was there an event such as a new Service Bulletin or software revision that coincided with the rise in removals; is there a particular phase of flight that the problem manifests (cruise, landing or takeoff); was there any maintenance event that occurred in the history of the unit that seemed to usher in the rise of removals (such as a repair or replacement of anything); etc.
  • Shake and bake: Subjecting the part to environmental extremes is commonly called ‘shake and bake’. This may involve putting the part into a freezer and then testing the part, putting the part in an oven then testing, and/or inducing a vibration during testing to see if anything fails. In fact this whole process can get quite sophisticated when you try to replicate the hot, cold, pressurized/unpressurized, or vibration environment that the particular part operates in.
  • Under the magnifying glass: This means examining the suspected part under a microscope or magnification of some strength to look for flaws that may not otherwise be detected with the naked eye.
  • Swapping parts: With the operator’s or airline’s permission, this involves swapping a subassembly from one unit into another and seeing if the problem follows. If the chronic unit comes back again, at least you’ve eliminated that subassembly from the list of possibilities, and the list narrows.
  • Replace suspected parts: Although the shop doesn’t see hard failures, you can at least make a logical, educated estimate that the problem comes from a certain area in the unit, and simply replace a few parts. Some call this ‘shotgunning’, but sometimes it really works. This can get expensive, however, particularly if it does not yield immediate results.
  • Flight testing: After a major effort to fix the problem, it may be possible to put the part on a flight test or operational aircraft accompanied typically by an engineer on the flight deck. If the part fails again, at least the engineer can gather more information as to the operational profile and crew procedures in affect at the time of failure; valuable insight.
  • Shoot the horse for crying out loud! There comes a time in the life of a chronic or rogue unit where the combination of operational delays or cancellations, parts replaced, and labor costs reach a point where you could have purchased a new or aftermarket replacement part. Of course this means removing the rogue from service. This is difficult sometimes, because maintainers hate to give into a challenging problem. Management simply has to make this call, and in fact it may turn out to be the most cost effective solution.


The obvious answer is to scrap the part. There are some in our industry however, that may try to salvage any value from the part, and recoup their losses by selling it on the aftermarket. This is unethical, and depending on the part, unsafe. The most unscrupulous of these persons would send the part to an unwitting repair station with the knowledge that the part is going to pass the routine tests. Now with a fresh 8130-3, the part is on its way to the aftermarket to start a new life with a new operator as a chronic unit. Fortunately, these types of persons who engage this activity are in a very small majority.



Before I get off this soapbox and turn in my laser-pointer and lapel mike, a few words: As I alluded to earlier, as regards chronic or rogue parts, tempers can flare on both sides of the Operator-Shop relationship. Allegations of poor quality at the Shop, or poor troubleshooting at the operator’s aircraft abound in this arena. Exacerbating this is when the operator is experiencing operational delays or cancellations (a source of passionate [there’s that word again] debate at any operator), or making warranty demands on the shop for the rogue’s performance, and it may not be the shop’s fault! My humble wisdom:

  • Operator: First acknowledge that occasionally you’ll own a part that becomes a rogue or chronic unit. Don’t be so fixated on turn-times, warranty claims, or allegations of poor quality that you actually dis-incentivize the shop from doing a proper job in addressing the rogue.
  • Shop: Don’t get in the habit of writing off all those ‘no trouble found’ responses to the operator’s perceived lack of troubleshooting skills at their aircraft. If you see a chronic part developing, don’t be so fixated on turntime goals that you don’t accomplish a proper job of addressing the problem.
  • Both: To the degree that most operators really want to encourage an atmosphere where their vendors are partners and team members, the environment should be characterized by a lack of fear to express problems, and for both parties to put aside the emotions and roll up their sleeves to fix the problem. Fortunately, most of you are just such players.

There are all kinds of deeper, more profound information regarding this subject, but this is just a primer on the issue.


By the way, it is my opinion that one of the characteristics of a true leader is that they unapologetically express certain issues with passion. Yes that can get you into trouble too, but hey, another leadership marker is the willingness to take measured risks…


Over ‘n out.

Posted By Roy Resto | 5/10/2011 9:34:34 AM