Repair Turnaround Time (RTAT)

Design for RTAT

System availability is a function of both reliability (inherent in the component) and maintainability. Maintainability is the ease with which a component can be sustained in order to isolate defects or correct defects or their cause, meet new requirements, make future maintenance easier, or cope with a changed environment. The design emphasis of maintainability is to reduce the maintenance burden and (and thus shorten the entire supply chain) by reducing the RTAT necessary to restore component capability when it malfunctions.

Myriad factors influence RTAT, but the preponderance of repair time required for any item, subsystem, or system typically is attributable to fault isolation. Thus it is imperative to provide the most effective diagnostic (troubleshooting) routines. Manual techniques - basically trial-and-error efforts by skilled technicians - should be eliminated at all levels of maintenance except depot/artisan. Auto- or semiautomatic techniques should be prescribed for unit level maintenance because unit maintenance is structured for quick turnaround based on minor repair/service/adjustment or ‘remove and replace’ concepts. This approach maximizes local weapons system availability. Test equipment, if necessary at the unit level, should be of the "go/no go” type, which requires minimal interpretation of signal data, all in order to reduce local RTAT, given its impact on mission capability and system availability at the organizational or unit levels.

The Technology Readiness Assessment (TRA), among the range of engineering technical reviews during an acquisition life cycle, is specifically a metrics based process that assesses the maturity of critical technology elements, including sustainment drivers, and is a good illustration of how a sustainment metric like RTAT plays a role in the design interface process. If a key enabler or sustainment driver (e.g., turnaround time (TAT)) does not meet required performance levels or significant performance advances are required over what is currently achieved with existing technology, then a plan for maturing the critical technology or process should be developed.
 
RTAT as a Metric

RTAT must be consistently applied and interpreted in order to be of value as a metric. The most usual definition of RTAT is elapsed time of repair – but does this include time awaiting maintenance, shipping times, awaiting parts time, etc.? RTAT is sometimes called simply TAT, or cycle time or elapsed maintenance time – there are many variations of similar, closely related metrics, as described earlier – whether driven by Service preferences, or other consideration, RTAT and related metrics must be explicitly defined – formula, specifics about how data is gathered, how often, by whom, in what manner, etc.
 
What matters is that all organizations using a given TAT-related metric concur on its definition, interpretation, currency, etc., and on how metrics are aggregated. For example, an RTAT metric is useful at the component level, but it rolls up into a more aggregated Mean Time to Repair (MTTR) at the subsystem level, and is a key part of Not Mission Capable-Maintenence (NMCM) calculations at the system level.
 
Sparing Process 

RTAT is a critical concept in both provisioning and maintenance planning. Wholesale inventory and sparing decisions are based in part on expected RTAT, since minimum systems spares must account for assets in or enroute to or from the repair cycle. In the wholesale provisioning world repair is the preferred source of supply for reparable items, and RTAT influences stockage level, maintenance induction timing and quantities at the tertiary maintenance level, Economic Repair Quantity (ERQ), and so forth. Actual repair-cycle times are used to compare against standards, with attention applied to either improve the repair-cycle process or correct the standards when actual repair times significantly deviate from the standards.
 
Retail demand-based sparing computations are also based on some calculation of localized turnaround time, i.e., anticipated number of maintenance replacements that will be repaired locally and the item's local repair-cycle time, with the similar goal to minimize the quantity of material placed on order and in storage throughout the DoD supply chain by balancing costs against supportability performance goals established with customers.
 
RTAT Role in Performance Based Product Support

Performance Based Logistics (PBL) Product Support Arrangements (PSA) formally document agreed levels of support and associated funding, required to meet performance requirements. PSAs include the objectives that form the basis of the PBL effort, including responsibilities and expected levels of support. Sustainment metrics inform the objectives that are the basis of PSAs.
 
Among a variety of factors, the outcome metric denoting user requirements, e.g., Materiel Availability (Am), is typically a balance between a quality metric (e.g., materiel reliability (Rm)), and a response metric (e.g., RTAT). Such response metrics may variably be stated as maintenance RTAT, maintenance Mean Time to Repair (MTTR), depot cycle time, negotiated Time-Definite Delivery (TDD), etc. However a program office chooses to define and track TAT, this telling value is key to a properly scoped PBL plan.
 
Depot RTAT

Depot repair cycle time is composed of two segments. These include the retrograde time segment (a collective term for the base-processing and in-transit times) and the RTAT segment (a collective term for the transfer-to-maintenance, maintenance shop, and transfer-from-maintenance times). Depot Repair Cycle Time (RCT) typically excludes Awaiting Parts (AWP) time, Awaiting Maintenance (AWM) time, or Awaiting Carcasses (AWC) time, as variables not consistently related to on-component repair work. Some other specific depot-related terms include:

• Base-processing time - Begins when an organizational- or intermediate-level maintenance activity determines that it cannot repair an unserviceable Depot-Level Repairable (DLR); it ends when the asset is ready for shipment from the base and is turned over to transportation.
• In-transit time -  Begins when transportation receives the ready-for-shipment unserviceable DLR and ends when the distribution depot or contractor processes the receipt transaction and the unserviceable DLR is recorded on the records of the Inventory Control Point (ICP).
• RTAT Time Segment - Depot RTAT is the sum of transfer-to-maintenance time, maintenance-shop time, and transfer-from-maintenance time. AWC time may occur before or after transfer-to-maintenance time and before maintenance-shop time, but is excluded from both of those times.
• Transfer to Maintenance Time - The transfer-to-maintenance time segment begins with pulling the unserviceable asset from storage and ends when the organic or contractor maintenance activity receives it. Transfers from depots to contractor facilities include transportation time.
• Maintenance Shop Time - The maintenance-shop time segment begins when maintenance artisans receive the unserviceable DLR and ends when the availability of the serviceable asset is formally reported to storage. (AWP and AWM times may occur during the segment, but are excluded.)
• Transfer from Maintenance Time - The transfer-from-maintenance time segment begins when the maintenance activity formally reports the availability of the serviceable DLR and ends when the serviceable asset is received in storage and is recorded on the records of the ICP. Transfers from contractors' facilities to depots include transportation; transfers to customers do not. Transfer from maintenance time does not apply when contractors act as DoD distribution depots, storing materiel and issuing it directly to customers.

Other Related Definitions:

• Maintainability - Design characteristic that makes possible the accomplishment of operational objectives with minimal expenditure of support effort and resources
• Corrective Maintenance Time - The time that begins with the observance of a malfunction of an item and ends when the item is restored to a satisfactory operating condition. It may be subdivided into active (work in process) maintenance time and non-active (not actively in work) maintenance time. It does not necessarily contribute to equipment or system downtime in cases of alternate modes of operation or redundancy.
• Mean Down Time (MDT ) - The average total downtime required to restore an asset to its full operational capabilities. MDT includes the time from reporting of an asset being down to the asset being given back to operations/production to operate. MDT also includes administrative time of reporting, logistics and materials procurement and lock-out/tag-out of equipment, etc., for repair or Preventive Maintenance (PM). MDT = Mean PM + Mean Corrective Maintenance (CM) + Mean Logistics Delay (MLD)/total number of failures.
• Logistics Response Tim (LRT) - The amount of time (measured in mean days) that elapses from the date a customer establishes a requisition to the date the customer receives the material that was ordered.        
• Retrograde Cycle Time - The amount of time elapsed from an item failure to the return of the asset to mission capable status. 
• TAT - The amount of time elapsed between when an action is initiated and its completion (could apply to maintenance, repair, logistics, etc.). Avg TAT = Sum of the elapsed times to make repairs/Number of repair jobs.
• LDT - Downtime that is expended as a result of delay waiting for a resource to become available in order to perform active maintenance. A resource may be a spare part, test, maintenance equipment, skilled personnel, facility for repair, etc.
• Ratio of Actual to Forecast Cycle Time - Measurement of the relationship between actual cycle time (e.g., retrograde, maintenance, repair) to forecast cycle time. Divide average actual cycle time by average forecast cycle time.
• Mean Maintenance Time (MMT) - A measure of item maintainability taking into account both preventive and corrective maintenance. Calculated by adding the preventive and corrective maintenance time and dividing by the sum of scheduled and unscheduled maintenance events during a stated period.
• MTTR - Total elapsed time (clock hours) for corrective maintenance divided by the total number of corrective maintenance actions during a given period. Divide the total number of hours of corrective maintenance during a given period by the total number of corrective maintenance actions during that period.
• RCT - Is the elapsed time (days or hours) from the receipt of a failed item at a repair facility (Intermediate, Depot, Original Equipment Manufacturer (OEM) or organizational maintenance unit) until the item is ready for reissue, or the average elapsed amount of time from an item failure to the time the item failure is repaired and placed in stock or reissued.
• Retrograde Ship Time (RST) - The average elapsed time from an item failure to the receipt of the item by the maintenance echelon specified to repair it. RCT = RST + TAT.
• Maintenance Down Time (MDT) - The total time during which a system/equipment is not in a condition to perform its intended function. MDT includes active maintenance time, logistics delay time and administrative delay time.
• Maintenance Man-Hours per Operating Hour - The number of maintenance man-hours required for each system operating hour (usually expressed as average). Divide the total number of maintenance man-hours by the total number of operating hours. Divide further by number of assets to determine maintenance man-hours per operating hour per asset.
• Direct Labor Hours (DLH) - The number of hours of work performed by direct labor personnel (e.g., touch labor, other directly attributable effort), measuring depot maintenance capability, workload, or capacity