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  2. Service Life Extension Program (SLEP)

Service Life Extension Program (SLEP)

ALCL 135


Modification(s) to fielded systems undertaken to extend the life of the system beyond what was previously planned.

Alternate Definition

There is no formally promulgated DoD-level policy on SLEP or the associated pre-SLEP analysis. Each DoD Component is responsible for Service Life Extension (SLE) planning within the boundaries of applicable legislative requirements and tailoring modernization and recapitalization programs to their respective requirements and constraints.    

Alternate Definition Source
General Information


The DoD SEBok provides amplifying information about SLE and the continued use of a product and/or service beyond its original design life. Product and service life extension assessment involves determining the risks and the life cycle costs of continuing the use of the product or service versus the cost of a replacement system. The SEBok goes on to say SLE is typically required in the following circumstances:

  • The system no longer meets the system performance or reliability requirements.
  • The cost of operation and maintenance exceeds the cost of SLE, or the available budgets.
  • Parts are no longer available for repair and maintenance.
  • Operation of the system violates rules or regulations, such as environmental or safety regulations.
  • Parts of the system are about to reach their operations life limits, which will result in the issue listed above occurring.

Key Factors

This reference source states that it is best if systems engineers and logisticians use a proactive approach that predicts ahead, so that SLE can be accomplished before the system fails to meet its requirements and before the operations and support costs rise above acceptable limits. In addition, the SEMbok notes that the following key factors that must be considered during a SLE:

  • Current life cycle costs of the system
  • Design life and expected remaining useful life of the system
  • Software maintenance
  • Configuration management
  • Warranty policy
  • Availability of parts, subsystems, and manufacturing sources
  • Availability of system documentation to support life extension

Associated Terms and Concepts

Other terms often associated with SLEP by the Services include the following:

  • Service Life Assessment Program (SLAP) - Is a generic term for the analysis of equipment preparatory to SLE, routine overhaul or reset of equipment with degraded military capability due to type or extent of usage.
  • Reset - Consists of actions taken to restore units to a desired level of combat capability commensurate with the unit’s future mission, sometimes in conjunction with service life extension. It can encompass maintenance and supply activities that restore and enhance combat capability, often including modifications or incremental upgrades, to unit and pre-positioned equipment that was damaged, stressed, rendered obsolete, or worn out due to combat operations by repairing, rebuilding, or procuring replacement equipment/components. Reset and SLE are basically the same process, but reset may happen repeatedly during a weapon’s life cycle, while SLE may only occur once. Both actions, however, can be driven by the same catalysts, and at any point along the life cycle continuum. These maintenance and supply activities involve depot and field level (i.e., organizational and intermediate) repairs/overhauls centrally managed to specified standards. Included are Procurement, Research Development Test and Evaluation (RDT&E), and Operations and Maintenance (O&M) funded repairs/overhauls and recapitalization (rebuild or upgrade) that enhances existing equipment through insertion of new technology or restoration of selected equipment to a zero-miles/zero-hours condition.
  • Reconstitution - includes actions beyond reset, taken during or after operational employment, to restore or upgrade combat capability to full-spectrum operational readiness. Reconstitution includes personnel, equipment, and training. Force reconstitution spans activities from normal sustainment (rearm, refuel, recovery, repair, and replace), through reorganizational regeneration of units to redeployment.

 US Air Force (USAF)

USAF reset/life extension policy is stipulated by Headquarters, USAF, which provides planning, programming and budgeting as well as strategy and policy, in conjunction with ongoing management of both acquisition and maintenance/supply. USAF reset is conducted at two levels:

  1. Major Commands (MAJCOMs) are responsible for operational requirements, forecasting reset requirements, and field level maintenance (support equipment and vehicles)
  2. Air Force Materiel Command (AFMC) is the lead command for sustainment, for depot planning and operations, and ongoing technology insertion (major end items, aircraft, engines)

Many factors are considered when establishing a USAF SLEP requirement. As a minimum, a SLEP requires engineering investigation to:

  • Determine scope and feasibility, to include structures, mechanical systems, propulsion, avionics, wiring, etc.
  • Establish the foundation for modifying the airworthiness certification
  • Execute the methods of compliance for each applicable airworthiness criterion

The minimum requirement for SLEP evaluation is to conduct a comprehensive Durability and Damage Tolerance Analysis (DADTA) and corrosion assessment to quantify expected, desired service life limit increase. To validate those analyses, durability testing at any level, flight testing or teardown inspections of high-time equipment may be necessary, especially if damage discovered in service varies compared to analysis and test predictions. Such testing is often referred to as a Full-Scale Durability Test (FSDT).
SLEP planning and development may involve several phases spanning many years. Example tasks follow:

  • Generate a baseline operational loads/environment spectrum update to include any planned future mission or usage changes.
  • Perform a corrosion assessment update and a DADTA update
  • Develop initial design changes based on what is already known from updated DADTA, service experience, and past durability testing with supporting DADTA, static strength analysis, etc.
  • Perform durability testing planning to include test article selection and acquisition, installation of instrumentation, development of test loads spectrum, verification of test loads spectrum, procurement of load control & data acquisition system, design and production of test fixture to include load application system, installation of test loading system and system checkouts.
  • Conduct durability testing, cycling and periodic inspections, collect and correlate strain gage and deflection data, obtain crack growth data when practical, and install repairs representative of fleet dispositions wherever practical, etc. as needed.
  • Conduct residual strength tests and perform teardown inspection and evaluation to include disassembly, visual inspections of all structure, non-destructive inspection (NDI) of all safety-of-flight structure and other locations based on analyses, fleet history, etc., and failure analyses.
  • Perform DADTA correlations with durability testing results to include development of Equivalent Initial Flaw Size (EIFS) values for all cracks discovered to support risk analyses.
  • Develop additional design changes based on test & updated DADTA results with supporting DADTA, static strength analysis, etc. Consider combining discrete design changes into larger integrated design changes when beneficial.
  • Perform ground tests of SLEP designs as necessary to validate the analyses such as static testing, durability testing, damage tolerance testing, ground vibration testing, etc.
  • Perform flight tests of SLEP designs as necessary to validate the analyses such as flight loads, ground loads, flutter, etc.
  • Iterate SLEP designs as required based on ground and/or flight tests of the design changes, if conducted.
  • Complete all change development tasks necessary to implement the design changes to include acquisition strategy, installation strategy, tooling (development, acquisition, manufacturing, sustainment, etc.), manufacturing instructions (planning, work control documents, technical orders, etc.), kits (development, acquisition, manufacturing, etc.) consumables, kit prototyping, kit proofing, installation training and spares provisioning.
  • Obtain Military Type Certificate (MTC) for the SLEP design.
  • Implement the changes and increase the SLL documented in the MCA for each aircraft when completed.

 The following are example initial questions to determine the overall scope of the SLEP:

  • What % increase in flights and flight hours (fatigue consideration)?
  • What % increase in years (corrosion consideration)?
  • Confidence level that further service life extensions will not be required?
  • Are there new mission types?
  • Are there new mission profiles?
  • Is there a new mission mix?
  • Is the new spectrum more/less severe than the baseline?
  • Are there any changes to the aircraft weight?
  • Are there new configurations (e.g., stores, payload)?
  • Are there planned modifications that may affect aircraft performance and therefore the aircraft loads/environment?
  • Does fleet history indicate a SLEP is required?

Once the overall scope of the SLEP is determined, the structures team must consider many factors to determine if Full-Scale Durability Test (FSDT) is required. In those cases where an FSDT is required to validate the DADTA and to demonstrate the durability life for the extended service life, an FSDT can add 5 to 7 years to the schedule, and extensive costs, so this is not a trivial decision. Additionally, unanticipated failures in the FSDT can lead to further cost and schedule increases. Therefore, weapons systems are closely monitored for changing failure rates and modes.

In summary, USAF SLE:

  • Is driven by both operations tempo (OPTEMPO) and regular maintenance plans
  • Is seen as opportunity to insert new technology into legacy fleets or recapitalize aging assets, minimizing downtime and operational impacts

US Navy (USN)

The USN's Depot Maintenance Strategic Plan and the corresponding strategic goals established by the Systems Commands (SYSCOM) create an industrial, flexible, dynamic partnership between organic Navy facilities, commercial suppliers, and other DoD depots. Depth, breadth, and “mix” of depot maintenance capabilities, and processes are traceable through the Chief of Naval Operations (CNO) maritime strategy to the Defense Strategic Guidance.

Two SYSCOMs are primarily responsible for depot level maintenance, reset and service life extension:

  1. Naval Sea Systems Command (NAVSEA) - The shipyards are unique in that they are resourced by the fleet and operated by NAVSEA. US Fleet Forces (USFF) Command resources the east coast depots, and US Commander Pacific Fleet (CPF) resources the west coast depots. These two organizations are responsible for the operational readiness of the surface fleet in their respective Areas of Responsibility (AORs). In this way, the operational fleet can manage their readiness without the distraction of managing the depots. Primary participants in USN equipment life extension, reset and overhaul include _
    • Naval Undersea Warfare Center, WA (maintains, repairs undersea weapons, ordnance, and associated equipment)
    • Naval Surface Warfare Center, IN (maintains, repairs fleet surface weapons, ordnance, and associated equipment)
    • Commander Navy Regional Maintenance Command, VA, FL, CA, Overseas (facilitates planning, contracting and management of private sector depots executing surface ship maintenance)
  2. Naval Air Systems Command (NAVAIR) / Commander Fleet Readiness Centers (COMFRC)  - Operates a system of Naval Aviation Fleet Readiness Centers (FRC) which provide maintenance, repair and overhaul of aircraft, engines/modules, components, support equipment and services. A list of the FRCs follows:
    • FRC East, Cherry Point, NC
    • FRC Southeast, Jacksonville, FL
    • FRC Mid-Atlantic, Oceana, VA
    • FRC Southwest, North Island, CA
    • FRC West, Lemoore, CA
    • FRC Northwest, Whidbey Island, WA
    • FRC Western Pacific, Atsugi, Japan
    • FRC Aviation Support Equipment (ASE), Solomon’s Island, MD

The naval aviation depot maintenance process is a shared responsibility between NAVAIR and the FRCs. NAVAIR leads aviation depot maintenance resourcing, industrial planning and policy. COMFRC leads organic industrial maintenance execution.

US Marine Corps (USMC)

The USMC conducts equipment life extension integrated with equipment modernization objectives, long-term support costs and strategic investment plans, anticipating no post-Iraq, post-Afghanistan “operational pause” wherein the service might have the luxury of focusing exclusively on reset and reconstitution. For example, post-Operation Iraqi Freedom (OIF) drawdown and reset was critical, given 4x to 9x normal equipment usage rates, and a concurrent accelerating Afghanistan ramp up. Equipment reset generally falls into four categories with defined logistics requirements/action, including the following:

  1. Procurement/Replacement  - Applies to equipment considered obsolete or potentially beyond economical repair
  2. Depot Maintenance - The upper limit for cost of repair for depot maintenance typically is 65% of the latest acquisition cost (exceptions may be evaluated on a case by case basis). Equipment repaired at designated depot-level repair activities will normally undergo 100% overhaul/rebuild. However, Inspect and Repair Only as Necessary (IROAN) and Selective Overhaul and Repair (SOAR) programs are viable options when determined to be a more effective and efficient means to return equipment to Full Mission Capability (FMC). Overhaul or rebuild includes upgrading, testing and inspecting of end items, parts, components, assemblies, and subassemblies. It also includes software maintenance and the installation of parts or components for modifications
  3. Field Maintenance - Includes equipment requiring field level maintenance, or equipment needed immediately, will be processed via field maintenance capability collocated with operational forces’ home station, and may include utilization of Contractor Logistics Support (CLS)
  4. No Reset  - Typically unique or non-system items that do not have a long term requirement within the Marine Corps, and which therefore will not receive maintenance action. Equipment being disposed of will follow standard DoD disposal procedures via the most expeditious and economical means available

OIF equipment reset policy was formalized in 2009 and provided concepts of operations, roles/responsibilities, metrics, modeling and IT considerations, transfer and supply procedures, etc.  The Operation Enduring Freedom (OEF) in Afghanistan and its equipment life extension policy was initiated and formalized in 2012, and included comparable structure and strategic considerations as the OIF process and OIF lessons-learned. The OEF equipment reset strategy set out to:

  • Leverage optimal repair locations, both outside the continental United States (OCONUS) and within the continental United States (CONUS). The ‘fix’ is completed as far forward as possible
  • Leverage “unit move” redeployment processes to maximize velocity and minimize transportation costs
  • Provide Service-level visibility of reset actions and maintain end-to-end visibility of all equipment through the redeployment and retrograde processes
  • Leverage Contractor Logistics Support (CLS) capabilities
  • Leverage OIF lessons-learned
  • Use USMC systems of record (i.e. Total Force Structure Management System (TFSMS), Supported Activity Supply System (SASSY), and Global Command Support System - Marine Corps (GCSS-MC) to enable accurate reset planning, decisions, and actions
  • Link ground equipment reset to modernization efforts and new / future acquisitions
  • Conduct equipment reset while continuing to support current operational requirements

Below is a categorization of equipment used to enable planning for strategic resources, position logistics, to anticipate CLS requirements and to forecast USMCs Overseas Contingency Operations (OCO) funding requirements by fiscal year:

  • Category I: Redeployment - Required to fill shortfalls at the Marine Expeditionary Force (MEF); the equipment reset strategy is to conduct necessary repairs at the MEF Intermediate Maintenance Activities (IMA) or CLS.
  • Category II: Retrograde - Applies if there is a deficiency at activities other than the operating forces; the equipment reset strategy is to conduct necessary repair at organic or external depots managed by Marine Corps Logistics Command (MCLC). Also applies to equipment excess to, but not identified for divestment from USMC inventories
  • Category III: Remains in-theater or Retrograde - MCLC will provide disposition instructions. Applies if the equipment is obsolete, expected to washout or identified as excess of shortfalls, or if no requirement exists

Other USMC SLE considerations included:

  • Acquisition Strategy - Significant amounts of OEF ground equipment were obsolete or beyond economical repair. Equipment repair cost that exceeds 65% of the replacement cost was reset through new acquisition. MCLC identified equipment that meets this criterion.
  • Depot-level Maintenance Strategy - Cost of repairs estimated between 40% - 65% of the replacement cost were reset according to the depot maintenance strategy. The maintenance capabilities of the MARFORs were also a contributing factor in determining if an equipment item was appropriate for depot maintenance. As determined by the reset strategy, equipment may undergo 100% overhaul and rebuild to return equipment to a fully mission capable condition.
  • Field-level Maintenance Strategy - Cost of repairs estimated not to exceed 40% of the replacement acquisition cost was generally reset according to the field-level maintenance strategy. Equipment requiring field-level maintenance was generally shipped to home stations or delivered to MCLC per the equipment item’s life cycle management plan.
  • No Reset Required - Reset did not generally occur on equipment that was mission capable or deemed available for immediate issue to the operating forces or the equipment, or unique to OEF operations with no long-term Marine Corps requirement. No maintenance action was taken, unless there was an immediate requirement to support other contingency operations or as identified by the Service life cycle management plan.
  • Measuring life extension progress
  • Reset and life extension actions must be able to be accurately measured, in terms of speed of return, costs, impact to readiness and projecting future requirements. Relying on unit level supply and maintenance readiness percentages alone is considered insufficient. A comprehensive Service-level data collection plan measures the numerous and complex aspects of executing equipment reset, to include:
    • The average rate of return of type equipment along transportation routes and nodes in support of redeployment and retrograde
    • USMC transportation costs associated to retrograde operations
    • The average time to induct equipment into maintenance and time to reset it, by location and organization
    • Monthly execution of OCO reset funds by repair location and type of equipment
    • OCO reset funds expended for non-Stores Account Code (SAC) -3 Principal End Items (PEI), by organization
    • Impact of reset actions on MEF readiness at home station
    • Progress against planned equipment drawn-down plan

 US Army 
The Army Materiel Command (AMC) reset its and joint partners' equipment after OIF/OEF to regenerate combat power for future deployments. This meant operating AMC's depots, arsenals, and plants at up to three times the rate AMC ran them at the height of the Vietnam War.
There is no overarching Army guidance or Standard Operating Procedure (SOP) regarding the SLE life extension process in the Army. It is more of an implied task on the part of the Program Manager (PM) as part of fleet management and Total Life Cycle Management (TLCM) – to evaluate system performance and determine when and if a life extension program is indicated. It has been addressed in different Army organizations as fleet management, recapitalization, or SLE. Specifically to facilitate drawdown in Iraq and build-up in Afghanistan, AMC established the Responsible Reset Task Force (R2TF) to rapidly retrograde equipment from theater and facilitate the life cycle management, repair and redistribution and of equipment.
The R2TF is a forward presence working with Army Central Command (ARCENT) to assist in prioritizing Army requirements and in establishing and maintaining visibility, accountability and transparency of equipment as it came out of Iraq. AMC was uniquely suited to play a pivotal role in the drawdown of equipment from Iraq and other theatres. As the executive agent for equipment reset, AMC provided management and oversight for the execution of field and sustainment level maintenance with the goal of rebuilding combat power while protecting dwell time for Soldiers.
Although unique to a given program office and equipment, in each reset/life extension case the basic process is the same. It begins with ongoing monitoring of system performance. In cases where system capabilities no longer seem adequate to the threat, due to performance degradation or change of threat scenario, an analysis of alternatives (AoA) might be performed to evaluate potential courses of action. Options would include replacement equipment or life extension, modification, or technology renewal. The next step would be to refresh applicable requirements documents, procurement strategies and product support strategies for presentation to the Milestone Decision Authority (MDA). Life cycle costs analysis is a key part of such considerations.
With increasing demand, much Army equipment is aging far more rapidly than projected. Army estimated that because of the higher OPTEMPO, rough desert environments, and limited maintenance available in theater, operational equipment fleets were aging 4 years for every year in theater, dramatically shortening their expected useful life. In general, the Army’s major systems were operating at rates that exceeded - sometimes by factors of five or six - their average operating rates in peacetime.
The Army recognizes three components of overhaul or life extension:

  • Replacement - An effort to buy new equipment to replace battle losses, wash-outs, obsolete equipment, and critical equipment deployed and left in theater but needed for homeland defense, homeland security, or other critical missions
  • Recapitalization - A rebuild effort that extends the equipment's useful life by returning it to a near zero-mile/zero-hour condition with either the original performance specifications or with upgraded performance specifications
  • Repair - A repair or overhaul effort that returns the equipment's condition to the Army standard. This includes the special technical inspection and repair program of aircraft

For additional considerations, refer to the Repair versus Replacement article.