Saturday, March 17, 2012

The quest for readiness-based sparing.… What are its essential characteristics?

Key descriptive characteristics found in ten different definitions of readiness-based sparing.  Each word’s font size reflects its relative frequency in the sampled readiness-based sparing definitions.  Wordle courtesy of

It’s a phrase that service parts managers in the aerospace and defense; maintenance, repair, and overhaul; and remanufacturing communities use, but you’ll never find it in a dictionary.  Yet each of these managers has their own notion of what the term readiness-based sparing means.
Last week’s blog offered the following definition of readiness-based sparing from the Supply Chain Integration organization within the Office of the Assistant Secretary of Defense (Logistics and Materiel Readiness) website:
“Readiness Based Sparing (RBS) is the practice of using advanced analytics to set spares levels and locations to maximize system readiness.” [i]
Short but sweet.
This week’s blog takes a different approach, reviewing U.S. Department of Defense regulations, inventory textbooks, technical reports and academic papers for their definitions of readiness-based sparing.  The results were surprising.  After reviewing several dozen sources, the ten best definitions were picked for closer examination.  These definitions came from a variety of services and organizations. (See the selected references at the end of this article for a complete listing of these sources.)
These ten definitions totaled just under 1000 words although some definitions were longer than others.  Key words and phrases describing the essential characteristics of readiness-based sparing were pulled from each definition, their terminology standardized, and then their frequency of appearance tallied.  Although this approach isn’t very scientific, and was certainly influenced by my interpretive skills, the following bar chart summarizes the most frequently referenced readiness-based sparing characteristics. 

The most frequently referenced readiness-based sparing characteristics in ten sampled references.

Not surprisingly, characteristics such as availability, system, cost, readiness, sparing, multi-indenture, and multi-echelon figure prominently in the Wordle as well as the frequency chart.  This consistency is encouraging and gives us a better idea of what characteristics are important to the community of spares managers and practitioners involved with readiness-based sparing.
Reviewing all of these technical documents for their definition of readiness-based sparing was certainly educational.  Possibly the most comprehensive definition of readiness-based sparing in the sampled documents came from a technical report written for the U.S. Coast Guard[ii]:
“Readiness-based sparing [RBS] is the process by which inventories are sized to support a major system or principal end item at levels that meet the customer's availability goal for operating that system or end item.  Appropriately, RBS is sometimes referred to as sparing to availability.  An RBS model is an inventory requirements model that sets levels that either minimize costs while meeting a system or end-item operational availability (Ao) goal or maximize the system or end item's Ao within a dollar limit….
“… [A]n RBS model seeks the best combination of item EBOs [expected backorders] in terms of the availability of the system or end item being supported….
“Other aspects of RBS modeling are multi-echelon and multi-indenture capabilities.  If an RBS model has a multi-echelon capability, its selection process considers the best location for that spare among all the echelons of supply supporting the system or end item. ….
“If an RBS model has a multi-indenture capability, its selection process considers the position of the item in the system or end item's configuration….
“The multi-indenture capability is incorporated by considering hierarchy in the computation of a spare's operational availability improvement.  Once the marginal analysis algorithm selects a spare in a hierarchical chain, the ratios for all items in the chain must be adjusted to reflect their new operational availability contribution.”
Well, with a good definition of readiness-based sparing in hand, future installments of this blog will go into more depth about these key descriptive characteristics and what they mean to a service parts manager.  For now, at least, we have a convenient starting point.

One final note …. In the 13 March 2012 on-line edition of the Washington Post, there was a very interesting article (at least for aviation buffs and logisticians J) titled “Aging DC-3s serve as ‘buses of the jungle’ in Colombia” by Juan Forero.[iii]  It was about the fleet of ageless DC-3 cargo aircraft (aka the C-47 Skytrain in its military designation) that ply the airways over Columbia.  Talk about a logistical challenge … try keeping 60 to 70 year old aircraft in a flyable status.  This article was definitely worth the read and the accompanying photos are very interesting too!  Here’s a link to the article:

In case you are not familiar with the DC-3/C-47, here is a picture of one.[iv]

     Douglas C-47 (photo courtesy of the U.S. Air Force)

Addenda (25 July 2016) - At this link, there is an excellent short video from the Smithsonian Channel about why DC-3s / C-47s are still flying ("Why the DC-3 Continues to Fly Decades After World War II").

Selected Readiness-Based Sparing References

1.   Department of the Army.  Logistics Provisioning of U.S. Army Equipment.  Army Regulation 700–18.  Washington, DC, Headquarters, 20 September 2009.  (Page 3)  Downloaded from on 6 March 2012.
2.   Department of the Navy.  Operational Availability of Equipments and Weapons Systems.­  OPNAV INSTRUCTION 3000.12A.  Washington, DC, Logistics Planning and Innovation Division (N40), 2 September 2003.  Enclosure 1: Operational Availability Handbook: A Practical Guide for Military Systems, Sub-Systems and Equipment; June 2003.  Project Manager James G. Smith, Deputy Chief of Naval Operations, Fleet Readiness & Logistics (DCNO (FR&L)), Logistics Planning and Innovation Division (N40), Strategic Planning, Logistics Processes and Acquisition Logistics Cell (N401A). (Page 14) 
3.   Department of the Navy.  Readiness Based Sparing.  OPNAVINST 4442.SA.  Washington, DC, Deputy CNO Fleet Readiness and Logistics (N4), 15 October 2011.  (Page 1)  Downloaded from, 4 March 2012.
4.   Geis, Mark B., et al, Implementing Readiness-Based Sparing in the Marine Aviation Logistics Support Program: Readiness Implications.  Alexandria, VA, Center for Naval Analyses, October, 2003.  (Page 34) Downloaded from, 4 March 2012.
5.   Gue, Kevin R.  Data and Models to Build Supply Blocks for Deploying Marine Corps Units. Monterey, CA:  Naval Postgraduate School, 7 October 1998. (Pages 3, 5)  Downloaded from, 5 March 2012.
6.   Menyhert, Carl F.  An Evaluation of the United States Army SESAME and Swedish OPUS VII Provisioning Models.  Master’s thesis, Naval Postgraduate School, Monterey, CA.  December 1983.  (Page 16)  Downloaded from 10 December 2009.
7.   Rodriguez, Christopher M. and Kevin Downer.  VMetric Spare Parts Optimization Model Validation. Report CG-D-06-98.  Groton, CT, U. S. Coast Guard Research and Development Center, July 1997.  (Page 3)  Downloaded from 2 April 2010.
8.   Sakulich, Capt Timothy J. and Lt Col Douglas J. Blazer.  Aircraft Availability Model (AAM) Weapon System Availability Targets.  Wright-Patterson AFB, OH: AFLC/MMM, 26 August 1988 (ADA 198832). (Page 1) Downloaded from 20 December 2011.
9.   Slyman, George L. and Dennis L. Zimmerman.  Improved Inventory Models for the United States Coast Guard Requirements Determination Process.  LMI Report CG201RD6.  Bethesda, MD: Logistics Management Institute, October 1993.  (Pages A-1 – A-4) Downloaded from on 8 March 2012. 
10. Spignesi, Nicholas A.  Implementing Readiness Based Sparing in the United States Marine Corps by Analyzing the United States Army’s Implementation Process.  Master’s thesis, Naval Postgraduate School, Monterey, CA.  December 1998.  (Pages 10-12)  Downloaded from, 4 March 2012.

[i] Supply Chain Integration OASD (L&MR), Readiness Based Sparing (RBS), downloaded from on 2 March 2012.

[ii] Slyman, George L. and Dennis L. Zimmerman, Improved Inventory Models for the United States Coast Guard Requirements Determination Process, LMI Report CG201RD6, October 1993, downloaded from on 8 Mar 2012.
[iii] Forero, Juan, “Aging DC-3s serve as ‘buses of the jungle’ in Colombia,” On-line edition of the Washington Post, 13 March 2012, downloaded from
[iv] U.S. Air Force photo, downloaded from on 15 March 2012.

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