“You say repairable, and I say reparable. You say rotable, and I say recoverable … So let’s call the thing exchangeable!” *



“Engineman Fireman Recruit Megan Cotrell conducts maintenance on an engine in one of the main spaces aboard the amphibious transport dock ship USS New Orleans (LPD 18).”[i] (Photo courtesy U.S. Navy)

 

There’s a term for everything in logistics. The problem is, the specific meaning of a term is often nuanced and depends on where you work or where you “grew up” as a logistician. Since every logistics organization has its own dialect, we take a closer look at several terms for spare parts, especially those parts managed by readiness-based sparing (RBS).

 

A closer look at terminology

Table 1 includes some of the more common terms and definitions for spare parts.  Use this table as a convenient point of reference...or translation; investigate the citations further to better understand the specific intent behind each usage.

Table 1 General Definitions

General term	Reference definition
Repair part	“Part required to return a vehicle to operational condition, necessary to perform its intended purpose. This does not include maintenance supplies; such as, wiping rags, antifreeze, radiator flush and stop-leak, solvents, grease, etc.”[ii]
Spare part	“An individual part, sub-assembly or assembly supplied for the maintenance or repair of systems or equipment.”[iii]
Service parts	“Those modules, components, and elements that are planned to be used without modification to replace an original part.”[iv]

 

Table 2 provides some additional specificity and definitions for spare parts based upon the item’s ultimate usage.

Table 2 Specific Definitions

The item is consumed or loses its identity in use.
Specific term	Reference definition
Consumable item	“An item of supply (except explosive ordnance and major end items of equipment) that is normally expended or used up beyond recovery in the use for which it is designed or intended.”[v]
Expendable item	“Item [that] is consumed in use or [that] loses its original identity during periods of use by incorporation into, or attachment upon, another assembly.”[vi]
Shop supplies	“Expendable items consumed in operation and maintenance (waste, oils, solvents, tape, packing, flux, welding rod).”[vii]
The item is not consumed and retains its identity while in use.
Specific term	Reference definition
Capital spare	“[C]apital spares are not consumed or used to destruction on the basis that they can be repaired and so become ‘rotable items’.”[viii]
Exchangeable item	“Recoverable components, such as pumps, electric motors, carburetors, and fuel controls.”[ix]
Recoverable item	“A spare part [that] normally is not expended in use and [that] can be reused after recovery and repair.”[x]
Repairable item	·       “An item that can be reconditioned or economically repaired for reuse when it becomes unserviceable.”[xi] ·       “A component, module, assembly, subassembly or equipment determined by the inventory manager to be economically repairable when it becomes unserviceable.”[xii]
Reparable item	“An item of supply subject to economical repair, and for which the repair (at either depot or field level) of unserviceable assets is considered in satisfying computed requirements at any inventory level.”[xiii]
Rotable item	“[R]otable spare parts are materials and supplies … that are acquired for installation on a unit of property, removable from that unit of property, generally repaired or improved, and either reinstalled on the same or other property or stored for later installation.”[xiv]
Rotable pool	“Supply's inventory of repairable items is commonly referred to as the ‘rotable pool’ or just the ‘pool’."[xv]
Note: Two definitions include qualifying statements.  The USAF definition for reparable includes this addendum: “This term suggests the logistics status rather than the condition of an item.”[xvi] The IRS definition for a rotable is further explained as: “flight equipment rotable spare parts and assemblies are tangible property for which depreciation is allowable while expendable flight equipment spare parts are materials and supplies.”[xvii]

Summary

In short, two broadly applicable definitions will work well in most logistics conversations regarding spare parts:[xviii]

1.     Consumable items are typically low-cost items that are consumed in use. Consumable items also lose their identity when installed on higher assemblies (you do not distinguish the part from the whole). It is usually physically or economically infeasible to repair failed consumable items—better to replace them. Common consumables include nuts, bolts, paint, wire, solder, memory chips, and brackets.

2.     Reparable items are high-cost items that are not consumed in use. It is often mechanically and economically feasible to repair these items. Examples of reparables (which retain their identity when in use) include items such as radios, radar units, engine components, or landing gear.

Readiness-based sparing methodologies are commonly applied to the management of inventories of reparable items and select (typically higher-cost) consumable items.

If you are still confused, don’t fret, you are not alone. The very etymologies of reparable and repairable differ.  Reparable comes from the Latin reparabilis meaning “able to be restored or regained,” while repair (and repairable) comes from the Latin reparare meaning “to restore, put back in order.”[xix]  Obviously, the need for repairing and maintaining equipment goes back a long, long time!



“Staff Sgt. Christopher Matthews, an aerospace propulsion systems craftsman with the 52nd Component Maintenance Squadron, inspects an F-16 Fighting Falcon exhaust nozzle March 16, 2010, at Spangdahlem Air Base, Germany.”[xx] (Photo courtesy of the U.S. Air Force)

* With a sincere thanks and acknowledgment to George and Ira Gershwin for their timeless music and corruptible lyrics. Also, a special thanks to Maggie Wise for her review and very helpful suggestions regarding this posting.

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[i] U.S. Navy Photograph by Mass Communication Specialist 2nd Class Dominique Pineiro/Released, USS New Orleans (LPD 18), downloaded from http://www.navy.mil/management/photodb/photos/120124-N-PB383-789.jpg on 6 Mar 2013. 

[ii] Department of the Air Force.  The USAF Supply Manual.  AFM 23-110, Vol I, Pt. 1, Chap 1, “General and Administrative,” Atch 1A-1 (Definitions and Supporting Information), Washington: HQ USAF, 31 Mar 2005. (p. 1-102)

[iii] McCann, Colonel John A., USAF (Ret.), ed. Compendium of Authenticated Systems and Logistics Terms, Definitions, and Acronyms.  AU-AFIT-LS-3-71.  School of Systems and Logistics, AFIT, Wright-Patterson AFB OH, 1981. (p. 637)

[iv] APICS, APICS Dictionary, definition downloaded from http://www.apics.org/industry-content-research/publications/apics-dictionary on 10 March 2013.

[v] Office of the Deputy Under Secretary of Defense for Logistics and Materiel Readiness (DUSD[L&MR]), DoD Supply Chain Materiel Management Regulation, DoD 4140.1-R, 23 May 2003. (p. 192)

[vi] Department of the Air Force, 2005. (p. 1-73)

[vii] McCann (p. 627)

[viii] United Kingdom Ministry of Defence. Defence Logistics Support Chain Manual.  JSP 886, Vol 2, Part 6 “Financial Accounting for Inventory,” Ver. 1-5, 5 February 2013, p. 8.  Downloaded from https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/73215/jsp886_vol2_pt6_fin_acct_for_Inv_v1-5.pdf on 22 Apr 2013.

[ix] McCann (p. 273)

[x] McCann (p. 571)

[xi] Department of Defense.  Department of Defense Dictionary of Military and Associated Terms, Joint Publication 1-02, 8 November 2010 (As Amended Through 15 October 2011). (p. 288)

[xii] Department of the Navy.  Supply Appendices.  NAVSUP P-485 Volume II - Supply Appendices, Revision 4, Glossary of Supply Abbreviations, Acronyms and Terms, Part B: Terms, Naval Supply Systems Command, NAVSUP HQ, 18 May 2009. (p. G-86)

[xiii] Department of the Army.  Logistics Provisioning of U.S. Army Equipment.  Army Regulation 700–18.  Washington, DC, Headquarters, 20 September 2009. (Page 31)  Downloaded from http://www.apd.army.mil/pdffiles/r700_18.pdf on 6 March 2012.

[xiv] U.S. Government, Internal Revenue Service.  Internal Revenue Bulletin: 2012-14, T.D. 9564 Guidance Regarding Deduction and Capitalization of Expenditures Related to Tangible Property, April 2, 2012.  Downloaded from http://www.irs.gov/irb/2012-14_IRB/ar05.html  on 14 Dec 2013.

[xv] Wirwille, James W. and William T. Ainsworth.  Analysis of a Proposal to Consolidate Aircraft Intermediate Maintenance Capabilities.  MS Thesis, Naval Postgraduate School, Monterey CA, December 1991 (AD-A246187). (p. 22)

[xvi] Department of the Air Force, 2005. (p. 1-102)

[xvii] U. S. Government.  Federal Register. Guidance Regarding Deduction and Capitalization of Expenditures Related to Tangible Property - A Rule by the Internal Revenue Service on 09/19/2013.  Downloaded from https://www.federalregister.gov/articles/2013/09/19/2013-21756/guidance-regarding-deduction-and-capitalization-of-expenditures-related-to-tangible-property on 14 Dec 2013.

[xviii] Pankonin, Captain George C. and Captain David K. Peterson. A Spares Stockage Algorithm for Low-Density Equipment. MS thesis, AFIT/GLM/33-82.  School of Systems and Logistics, Air Force Institute of Technology (AU), Wright-Patterson AFB OH, September 1982 (ADA123709). (pgs. 8-9).

[xix] Harper, Douglas. Online Etymology Dictionary.  http://www.etymonline.com/index.php?allowed_in_frame=0&search=repair&searchmode=none.  Accessed 14 December 2013.

[xx] U.S. Air Force Photograph by Airman 1st Class Nick Wilson, downloaded from http://www.af.mil/News/Photos.aspx?igphoto=2000293449 on 15 December 2013. 

Availability Makes a Difference … (Part II)











The Modular Airborne Fire Fighting System II (MAFFS II) being installed in a C-130 at Peterson Air Force Base, CO in 2009.[xxii]  (Photo courtesy of 302 AW, Air Force Reserve Command)

  

The MAFFS II as installed in a C-130 cargo bay, Peterson Air Force Base, CO in 2012.[xxiii]  (Photo courtesy of 302 AW, Air Force Reserve Command)

On 23 June 2012, a wildfire was quickly growing in the vicinity of Colorado Springs, CO.  Ultimately known as the Waldo Canyon fire, this fire lead to the U.S. Forest Service’s (USFS) 24 June 2012 decision to activate its Modular Airborne Fire Fighting System II (MAFFS II) for the 2012 wildfire season.[i] “On June 25 … MAFFS-equipped C-130s … received their first launch orders for 2012 and began to fly fire suppression missions on what would become the costliest wildland fire in Colorado’s history.”[ii] By 17 September 2012, when the MAFFS was deactivated for 2012, eight MAFFS equipped C-130s had “released almost 2.5 million gallons of fire retardant during 1,011 [aerial] drops on fires in 10 states.”[iii]

So, what is the MAFFS system? 

“MAFFS is a joint Defense Department and U.S. Forest Service program designed to provide additional aerial firefighting resources when commercial and private air tankers are no longer able to meet the Forest Service's needs ….

As a self-contained aerial firefighting system owned by the U.S. Forest Service, MAFFS can discharge 3,000 gallons of water or fire retardant in less than five seconds, covering an area a quarter of a mile long by 100 feet wide. Once the load is discharged, it can be refilled in less than 12 minutes.”[iv]

There are three Air National Guard wings and one Air Force Reserve Command wing that are MAFFS-qualified and provide the C-130 aircraft when the USFS activates MAFFS.[v] 

Why are these aerial firefighting systems so critical? According to the USFS’s January 2012 Large Airtanker Modernization Strategy, “Airtankers are used to deliver fire retardant to wildfires, thereby reducing fire intensity and rate of spread until ground personnel can reach the fire. Airtankers play a key role in successful initial attack, which is one of the most difficult and critical components of wildfire management.”[vi] The USFS report goes on to state that up to 70,000 communities across the U.S. are at risk of wildfires, and the annual costs of suppressing and recovering from wildfires “amounts to billions of dollars each year.”[vii]

Like any complex mechanical system, maintaining the MAFFS units and keeping them available requires skilled technicians, proper tools and equipment, and a ready source of spare parts. A 7 July 2012 article in The Seattle Times notes that the “Forest Service has stockpiled enough major parts, can source many smaller parts, and can mend the biggest parts no longer being made to keep the system running”[viii] according to Scott Fisher, MAFFS coordinator for the Forest Service. The article continues, quoting Mr. Fisher, "The system was built for at least 20 years … I would not be surprised to see this thing fly for a full 30 years."[ix] 

Of course, to make that projection a reality is where applying readiness-based sparing (RBS) and its availability-based sparing recommendations would be invaluable. For example, RBS can determine the proper range and depth of spare parts to keep the MAFFS units fully operational and available to continue their wildfire suppression mission for another 20 to 30 years.

System availability revisited

As noted in a previous posting on this blog, the availability of a fielded system in normal operations is dependent upon its supporting maintenance infrastructure. There are two basic categories of maintenance. The first category, corrective (or unscheduled) maintenance, generates independent part demands which must be forecasted. The second maintenance category, preventive (or scheduled) maintenance, generates dependent parts demands whose timing and quantities are derived from the maintenance schedule. Modern RBS applications can accommodate both of these maintenance types when sizing supply support.  Let’s now take a closer look at some well-known availability relationships.

Inherent availability

When it is important to examine the reliability-maintainability trade-offs for a system’s design, then inherent availability is an appropriate system performance measure.[x] Inherent availability [A_i] is calculated as (EQ. 1)  [xi] 

 

where the mean time between failures (MTBF) is (EQ. 2) [xii]

and mean corrective maintenance time  (also called Mean Time to Repair) is “For a sample of repair actions, a composite value representing the arithmetic average of the maintenance cycle times for the individual actions.”[xiii]

Operational availability

Unfortunately for operators and logisticians, the systems they support don’t operate in such an ideal environment and operational availability [A_o] becomes the more appropriate measure (EQ. 3) [xiv]

 

where MTBM is the mean time between maintenance. According to the DoD Reliability, Availability and Maintainability (RAM) Guide, MTBM considers “all maintenance actions, including repairing design/manufacturing failures and maintenance-induced failures, performing preventive maintenance, and other actions (e.g., remove an item to facilitate other maintenance).” [xv]

Mean maintenance downtime (MDT) measures “the total elapsed time required (when the system is not operational) to repair and restore a system to full operating status, and/or to retain a system in that condition. MDT includes mean active maintenance time (M bar), logistics delay time (LDT), and administrative delay time (ADT).[xvi]  In this definition, M bar is the actual hands-on maintenance time [xvii]; LDT is the time maintenance is delayed due to the lack of a spare part, maintenance facilities or equipment; or transportation [xviii]; and ADT is the time maintenance is delayed due to personnel availability, workload scheduling, etc.[xix] It is important to note that implicit to these availability calculations is the assumption that they represent the long-run average performance for a system.

Availability applications

The above measures describe availability from a traditional logistics viewpoint. RBS practitioners have adapted these definitions to support their day-to-day management of reparable item inventory systems, viewing availability as the product of maintenance and supply availability. In later posts we’ll define supply availability from the RBS perspective more precisely, but for the time being a reasonable working definition is “What is the probability that any randomly selected end-item (e.g., an aircraft) in a fleet is not down due to the lack of a spare part.” 

Stockage policy has a dramatic effect upon supply performance, and is how RBS influences the systemwide availability performance measure. Accurately estimating this performance is critical, especially when you are sparing for a small fleet of high demand assets such as the MAFFS II units and their C-130 aircraft. If the fleet has insufficient availability, then missions may be scrubbed and lives and property (in the case of wildfire fighting) will be placed in jeopardy.

Postscript

On 1 July 2012, MAFFS 7, the call sign for a MAFFS II equipped C-130 from the 145^th Airlift Wing at Charlotte-Douglass Airport, NC, crashed while performing its fourth airdrop of the day over a South Dakota wildfire.[xx] [xxi] Four North Carolina Air National Guard crewmembers were killed – Lt Col Paul K. Mikeal, Maj Joseph M. McCormick, Maj Ryan S. David, and SMSgt Robert S. Cannon and two crewmembers were seriously injured (names not released). 

For more information about MAFFS 7, there is a very touching memorial page to this brave crew at http://www.nc.ngb.army.mil/PAO/News/Pages/MAFFS.aspx . Our hearts and prayers go out to the members, families and friends of this crew.

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[i] Skarban, Ann. “MAFFS 2012,” Citizen Airman, Vol. 64, No. 5: 14-17 (October 2012).  Downloaded from http://www.citamn.afrc.af.mil/shared/media/document/AFD-120927-026.pdf on 31 Oct 2012.

[ii] Skarban (p. 14).

[iii] Air Force News Service (AFNS), “Forest Service deactivates C-130 firefighting operations,” 17 Sep 2012.  Downloaded from http://www.af.mil/news/story_print.asp?id=123318258 on 20 Sep 2012.

[iv] AFNS, 17 Sep 2012.

[v]  U.S. Air Force, “Fact Sheet: Modular Airborne Fire Fighting System,” (undated) downloaded from http://www.af.mil/information/factsheets/factsheet_print.asp?fsID=10566&page=1 on 13 July 2012.

[vi] USDA Forest Service.  Large Airtanker Modernization Strategy.  17 Jan 2012. (p. 2)  Downloaded from http://www.fs.fed.us/fire/aviation/airtanker_modernization_strategy.pdf on 26 Aug 2012.

[vii] USDA Forest Service (p. 3)

[viii] Gruver, Mead, “Some experts worry about a lack of parts for C-130 wildfire sprayers,” The Seattle Times, 7 July 2012.  Downloaded from http://seattletimes.com/html/nationworld/2018631369_forestfires08.html on 5 Sep 2012.

[ix] Gruver, 2012.

[x] Ebeling, Charles E. An Introduction to Reliability and Maintainability Engineering. Long Grove, IL: Waveland Press, Inc., 1997. (p. 255)

[xi] Blanchard, Benjamin S.  Logistics Engineering and Management (Second Edition).  Englewood Cliffs, NJ: Prentice-Hall, Inc., 1981. (p. 66)

[xii] Blanchard (p. 400)

[xiii] Department of Defense. DOD Guide for Achieving Reliability, Availability, and Maintainability. Office of the Under Secretary of Defense (Acquisition, Technology and Logistics).  Washington: 3 August 2005. (p. 3-8)

[xiv] Blanchard (p. 67)

[xv] DoD RAM Guide (p. 3-11)

[xvi] Blanchard (p. 46)

[xvii] Blanchard (p. 45)

[xviii] Blanchard (p. 46)

[xix] Blanchard (p. 46)

[xx] Church, Aaron M., ed. “Four Airmen Die Fighting Western Wildfires,” ­Air Force Magazine, Vol. 95, No. 8: 10 (August 2012).

[xxi] Schogol, Jeff, “Legacies remain for airmen killed in C-130 crash,” Air Force Times, 16 Jul 2012, p. 16.
[xxii] Air Force Reserve Command, downloaded from http://www.302aw.afrc.af.mil/shared/media/photodb/photos/110909-F-XU932-0171.JPG  on 12 Sep 2012. 
[xxiii] Air Force Reserve Command, downloaded from http://www.302aw.afrc.af.mil/shared/media/photodb/photos/2012/07/120627-F-IG195-644.jpg  on 12 Sep 2012. 

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