CAVU Café: Royboy’s Prose & Cons

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Cannibalizing, Robbing, and Swapping Aircraft Parts

I’d like to add a new choice of terms to our ever evolving aviation lexicon. When an aircraft reaches the end of its life and it’s being parted out, we’re not removing the parts- we’re harvesting the parts from the legacy asset.

A word that has managed to survive the trendy, revisionist makeovers is ‘cannibalize’, as in cannibalizing aircraft parts. Used interchangeably is the equally, potentially offensive word, ‘robbed’ aircraft parts. My, oh my, I’m wont to retreat to a safe place and curl into a fetal position at the use of such utterances. We certainly need kinder-gentler expressions! But guess what? They’re here to stay. Get over it.

So…what are we talking about? A likely scenario:

An aircraft is at the gate for the first flight of the day and passengers are loading. By the way, at any given airline, the bank of first flights is closely monitored in real time by many different organizations, and the percentage of flights making it out of the chocks on time is a key performance metric; this, since any delay or cancellation is going to have a cascading effect on the subsequent flights of the day. For the first flight of the day, the flight crew has to perform lengthier aircraft systems checks, and during these checks our air crew observes a fail during a bite test (Built-In-Test-Equipment). The air crew consults its MEL (Minimum Equipment List) and confirms the failure can’t be deferred; it must be fixed. The aircrew calls its Maintenance Operations Control center (MOC), who dispatches technicians to the aircraft. The techs note that the Fault Isolation Manual (FIM) requires the replacement of an LRU (Line Replaceable Unit). The problem is there is zero stock; and the parts-pooling partners are similarly zero stock; drats! These savvy technicians know however, that an identical aircraft is parked on the ramp awaiting lengthy repairs due to a bird strike. The techs call MOC for authorization to take the part off the idle asset, and use it on the now-waiting aircraft full of passengers. Twenty minute later the techs are on the flight deck signing off the offending write-up with the aircrew, and minutes later the tug spews its first puff of smoke as the aircraft backs out of the gate. In many an airline’s GMM or GPM (General Maintenance Manual or General Procedures Manual; in the USAF the equivalent is Air Force Instruction 21-101, Aircraft and Equipment Maintenance Management), this procedure is referred to as cannibalizing or robbing the part. To be sure, there are probably, other more kinder-and-gentler titles of the procedure, but these are the prevalent ones.

In the USAF, the same action is also called cannibalizing, and only certain Maintenance Management persons are certified to authorize such an action on the scene. I had this certification. Without doubt, cannibalizing or robbing must always be an option of last resort; all efforts must be expended to locate the part first from normal supply channels. It is no surprise then, that cannibalization rates in the airlines or military are a closely monitored metric since it reflects on the effectiveness of the inventory control system. Higher cannibalization rates tend to be accepted through clenched teeth for parts that are out of production. Higher rates may also be the natural consequence of operators who deliberately choose to be under-spared for certain assets to conserve cash.

Up to this point, the process to rob that part sounds easy…but it’s not. Consider the following:

  • Before the part is robbed (yes I switched to using this other term, from cannibalizing, since it’s easier to type), you must establish that the aircraft being robbed from has no existing write-ups against the system you intend to rob the part from. This is routinely accomplished by exam of the aircraft log book or equivalent electronic listing. In many cases you’re looking for the associated ATA chapter system. The idea here is that if the ATA system you intend to rob the part from has no write-ups, you can reasonably conclude the part remains in airworthy serviceable as installed.
  • The logbook entries in both the aircraft involved must be made precisely and in accordance with the written procedures.
  • In many cases, the part was initially ordered against the original aircraft with the write-up before the discovery of zero-inventory was confirmed. Since the part has now been robbed to fill the need, procedures must include that the part-order be amended to show that the aircraft robbed-from is now in need of it.
  • Many procedures I’ve seen require that as soon as the part is removed from the robbed-from aircraft, a tag must be affixed. Often it is this tag that facilitates the corrections to inventory orders previously discussed.
  • There are two special cases for close attention when considering robbing a part:

           o Is it a part that has scheduled overhaul or other maintenance requirements? If so, the airline’s tracking system must be amended to show the current                    installed-position of the part.

           o Is the part an LLP, Life Limited Part? My experience is that these parts are rarely robbed since nearly all require extensive disassembly in order to                          facilitate the removal and installation. Nonetheless, it remains a possibility and must be carefully considered for remaining time or cycles and to be                        tracked as concerns its current installed position.

How about swapping?

Swapping exists for one reason: To facilitate the troubleshooting process. For example, an aircraft has a write-up, but experience has shown that several LRUs (Line Replaceable Units) are equally capable of causing the fault. Any experienced technician will tell you that there has never been written a perfect Troubleshooting Logic Tree or FIM. Swapping parts that are the same part number to see if the fault is eliminated, or follows to the other swapped position, is really a great troubleshooting tool to confirm the source of the fault. This also helps reduce those pesky No-Fault-Found (NFF) charges. There are two scenarios for swapping:

     1. Swapping in the same aircraft tail number:

         Due to redundant aircraft systems, it is not unusual to find the same part number LRU installed for a Right or Left system, or in some cases a left, center,               and right system, or system 1, 2, 3, or colored systems. It’s been my experience that technicians often perform this type of troubleshooting without the                 necessity of informing anyone or filling out any tags or other documentation. The conscientious technician always will return the parts to their original                   positions once the troubleshooting process has concluded. In some cases the airline may have a hard rule that any such activity is strictly documented                   in accordance with their manuals, and for good reasons.

     2. Swapping between aircraft of different tail numbers.

         In some cases, this is the preferred or only option for swapping during troubleshooting. In this circumstance there are usually strict controls on                             documenting the actions taken.

If you know of any kinder-gentler, mood-ameliorating terms in use to describe these actions don’t hesitate to post a comment.

Over ‘n out

Roy “Royboy” Resto

Posted By Roy Resto | 4/2/2018 9:36:53 AM

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