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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


Reducing Component Turn Around Time, TAT: A Holistic View

Reducing Turn Around Time (TAT) seems to be on a perpetual hit list among writers of journals, case studies, and contracts. Indeed, what a nobler topic to champion? Speedier TAT’s result in greater availability of the asset being turned around. For aircraft this means more Revenue Kilometer Miles; for engines and components, greater availability of spares, or a reduction in spares inventory- music to the ears of CFO’s. What irks me however, and compels me to pen this blog, is that most of what has been written seems to exhibit a myopic focus on a single contributor to TAT: the supplier, and further, to lack frank honesty and comprehensiveness. If the goal is greater availability of the asset, the enlightened discussion must transcend this single contributor. In this blog I hope to present a frank picture of the entire Rotable TAT Cycle logistics chain; the holistic view.


Many contracts with MRO providers will contain a TAT performance provision. These contracts likely define what TAT means, when the TAT ‘clock’ starts and stops, and the penalties for the lowly supplier not meeting the stated TAT’s. Let’s broaden our scope. Every operator, including Airlines, the Military, and General Aviation (collectively ‘operator’) has their system to control the logistics aspect of the operation deemed necessary to support the maintenance of the fleet. This system typically controls the allocation of the stations with the spares, the number of spares, minimum stocking levels, parts in the ‘pipeline’ etc. The holistic discussion of the Rotable TAT Cycle falls into four distinct divisions:

  • Time at the operator during the removal process
  • Freight time to and from the supplier
  • Time at the supplier
  • Time at the operator while being returned to stock



Let’s put the hole in holistic. When should the whole TAT clock start? That is the fundamental segway into this holistic discussion. Simplistically, it starts at the operator. A Mechanic/Technician/Engineer (herein Technician) will draw the part from stock. At that point a ‘hole’ is recognized by the operator’s logistic system; that a spare is no longer available. Thumb on stopwatch please.


  • For the sake of simplicity we are starting the stopwatch at the moment the part is drawn from stock. In fact there are many instances where the knowledge of the requirement to draw from stock was known well ahead of the moment of the draw. For example, let’s follow the rotable cycle of a cockpit window. During a maintenance check inspection, the cockpit window is written up for excessive crazing. It is known that the window will have to be replaced. How long did it take between this known condition, and the time the part was ordered and drawn from stock? If the part was not in stock, how long did it take for the backorder to be placed? Since there are so many variables in answering those questions, the answer is likely not easily quantifiable as an average, but the point is made that there is likely room for improvement as may be identified by Lean and Industrial Engineers. 
  • So then, we are back to the window being drawn from stock, the clock ticking, and the ‘hole’ created in the logistics system  which now recognizes one less spare. Note the part requiring maintenance is still on the aircraft. A review of the AMM (Aircraft Maintenance Manual) reveals that several Avionics control panels will have to be removed to facilitate this maintenance, so there will a delay in the removal and installation of the cockpit window. The big-picture guys in Maintenance Control start to get nervous about this and other open maintenance jobs bumping up against the scheduled return to service tim for this aircraft. The installation and ‘signing off’ of this job now becomes the high priority for the Technician. The crazed window was removed and set aside while the serviceable window was installed and the paperwork completed to close the task and appease the honchos in Maintenance Control. It is not unusual that when crunch time comes for the return of the aircraft, and there are many open maintenance write-ups, technicians may get rapidly re-assigned to another task, and the turning-in of our unserviceable crazed window became a low priority, after all, getting the plane out on time is always the number one goal. Alternatively it may have been the end of his shift, and the Technician simply waits to turn-in the window until the next day, or ask a colleague on the other shift to turn it in. This action is not as easy as walking over to the stock room and giving it to them; paperwork must be accurately completed by the technician to accompany the window.
  • The unserviceable window finally gets turned in to supply/stores. Now what? If it was the only part requiring processing, it is likely it would receive immediate attention, but during an aircraft maintenance check it is routinely one of many turn-ins during this shift, and the current priority of supply employees are to issue parts required to close out those other open write-ups. Finally, the supply employee starts to process the turn-ins. Originally, the serviceable issued window was given to the technician in its storage box made of foam-in-place protection. The Technician had to tear apart the box to get to the window. This rendered the box unusable, and the unserviceable window turned in without a box, so the supply person hopes to find an unused ATA Spec 300 package for our window. None found for our odd shaped window. A fresh foam-in-place box takes shape, or the part waits for the crating shop to make a properly protective shipping crate. Now the paperwork can commence to ship the part to the supplier. Paperwork and packaging now complete, the part is placed in a designated freight pick up area.
  • Let’s summarize this segment of the Rotable TAT Cycle at the operator, and those areas we could measure for possible improvements.

                   o  How long did it take between the time the inspection’s write-up was created (which identified that the part needed 

                       replacement), and when the unserviceable part was removed?

                   o  If the part was not in stock, how long did it take between the time the inspection’s write-up was created (which 

                       identified that the part needed replacement), and when the backorder was created?

                   o  How long did it take for the part to issue once ordered? Did it have to be delivered from another warehouse or

                       location; a pick ticket issued and closed, the computer transactions, etc.?

                   o  How long did it take between the time the unserviceable part was removed at the aircraft, and then properly turned in

                       to supply?

                   o  What was the elapsed time since supply took-in the unserviceable part until it was placed for pickup?




One time a colleague misspelled freight as fright, and of course it was not corrected by spellcheck. He became the person credited as putting the fright in freight. And indeed, fright is a component of freight, primarily due to its costs. Costs and delivery times vary widely from Sterling service to ground delivery. Let’s look at some of the variables

  • Sometimes either the supplier or the operator will enjoy the upper hand in discounted freight costs. COMAT (the operator’s owned delivery assets such as its aircraft and counter-to-counter service) may also influence the picture. Either the supplier or operator may thus be tasked with the freight burden. 
  • Historically, if the operator was responsible for freight, the days in transit to and from the supplier have not been used in calculating TAT. If however, the supplier was responsible, this transit time was included in traditional TAT calculations.  Hmmm. The holistic view must account for this time regardless.



As mentioned earlier, this segment of the rotable TAT cycle is nearly universally the single topic of discussion in published literature, so I’ll only dwell on a few of the more interesting variables.

  • Suppliers with robust quality systems such as AS/EN or ISO standards usually have a myriad of internal performance measurements which will include TAT. When does their own clock start? Routinely, it starts when the work or repair order is opened. They may also apply this start of the clock to the customer’s TAT. What if the supplier is behind? What if the supplier’s manager decides to ‘park’ the just-delivered window for a couple of days before opening the repair order to relieve shop pressure? Hmmm….
  • Some types of work at the supplier will require that the part be inspected, and a quote of the estimated costs submitted to the operator before work can commence. During the time the quote is submitted and approved, operators conveniently allow or require that the TAT clock be suspended. You would be surprised at the number of operators that harp on TAT, yet take seemingly extraordinary time in responding to the required quotes they have imposed.
  • There are some instances where the spare parts used to repair or overhaul the rotable are provisioned or ordered by the operator. An efficiency study of this type of arrangement, and its contribution to TAT would be revealing.




The delivery truck roll-up door opens and the boxed, now serviceable window is unloaded. Is that it? Is the hole now filled? Not so fast. Let’s look at some of the variables.

  • The part is now put on the proverbial conveyer belt to be received. This may involve the time taken to fill out and attach the operator’s own serviceable tag
  • Some operators will require a more thorough inspection of the part before being placed into stock. The part may go to a ‘home shop’ or QC area for the inspection. How much time will that take?
  • Some operators will only receive parts at a centralized location. The hole may not exist at that location. This will require an additional shipment to the location with the need. This too was not likely to be on anyone’s stopwatch.



Any research literature or informative article on TAT that does not reflect this holistic view does its audience a disservice, and helps perpetuate the view that the sole contributor in the Rotable TAT Cycle is the supplier (Industrial Engineers are heard to be clapping in the background). The bottom line is that in the Rotable Cycle, there is room for improvement at every level, and only by a frank and open discussion can improvements be made.


PS: I looked up “holistic” in the dictionary before I started to use it, and discovered there is nothing ‘Holy’ about it. Shouldn’t it be ‘wholistic’? Alas, my major was not in English…

Posted By Roy Resto | 7/21/2011 11:36:48 AM