maintainability and availability · 2015. 4. 28. · rm&a measures maintainability measures •...

Maintainability and Availability

Agenda• RM&A Measures (Maintainability and

Availability)• Availability Mini-Exercise• Summary

Shifting Gears to Maintainability and Availability

We are available when you need us!

Maintainable!

Let’s have an example of maintainability

RM&A Measures

Maintainability Measures• MTTR = A basic measure of maintainability.

The sum of corrective maintenance times divided by the total number of repairs of the item. The average time it takes to fully repair a failed system. Typically includes fault isolation, removal, and replacement of failed item(s) and checkout.*

• Not considered:– Frequency of corrective maintenance actions– Number of man-hours expended

• Not a good measure of maintenance burden

Maybe an image of an “average” mechanic working on an “average” repair task with a supervisor watching his work and holding a stop watch or with a prominent clock in the background?

* Army Regulation 702–19 “Reliability, Availability, and Maintainability” dated 28 April 2015 Pg 24

RM&A Measures

Maintainability Measures• MaxTTR (Maximum Time To Repair) –The maximum time required to complete a specified percentage of all maintenance actions. For example, if a system specification indicated MaxTTR (95 percent) =1 hour, this means that 95 percent of all maintenance actions must be completed within one hour. *


RM&A Measures

Maintainability Measures• Mean Time Between Maintenance Actions (MTBMA)

– A measure of reliability that represents the average time between all maintenance actions, both corrective and preventive.*

– Used for statistically oriented maintenance analysis– Frequently used in availability calculations

* DAU Glossary - https://dap.dau.mil/glossary/pages/2234.aspx

RM&A Measures

Maintainability Measures• Maintenance Ratio

– A measure of the total maintenance manpower burden required to maintain an item. It is expressed as the cumulative number of manhours of maintenance expended in direct labor during a given period of the life units divided by the cumulative number of end item life units during the ‘same period.*

– Includes corrective & scheduled maintenance

– Usually excludes off-system repair– Valid for all maintenance levels– Must clearly identify system operating hours– A good relative comparison of the

maintenance burden of alternative systems


RM&A Measures

Availability Measures• Availability is a measure of the degree to which an

item is in an operable state and can be committed at the start of a mission when the mission is called for at an unknown (random) point in time.*

• Operational Availability (Ao) considers the effects of the OMS/MP, reliability, maintainability (including preventive maintenance), and administrative and logistics delay time (also referred to as mean logistics delay time ). Ao can be described by the following equation: Ao=uptime/total time.*


Maintainability Mini Exercise• Take a look at the items around you• Each team pick one item (laptop, cell phone,

tablet, stapler, printer, laser pointer, marker, etc…)

• Make a quick assessment (5-10 minutes) of its maintainability– Components (how many can you see/imagine)– Fasteners– Ease of access to components and visibility– Instructions handy?– More?

Assessing Maintainability

• Testers commonly do the following, to assess maintainability:– Collect data (often in conjunction with other test

events), and calculate MTTR, MR, etc.– Data, questionnaires, & observations from actual

maintenance procedures (as these are conducted)– Data, questionnaires, & observations from M-Demos– Other sources of data, such as M&S, design reviews,

or contractor maintenance data

Maintainability Demonstration

• Formal “proof” of achieved system maintainability (Final Exam)– Test cases are based on analysis of expected

maintenance actions (frequency, severity)– Some organizations perform M-Demo on all

maintenance actions (preventive, corrective), prior to fielding

• M-Demos are sometimes conducted on prototypes– Results are used to improve system design

• M-Demos sometimes conducted “virtually”

Maintainability Demonstration (cont.)

• Perform maintenance action & measure time required for each step– Assess ease of maintenance, maintenance

procedures, manuals, tools, etc.

• Ideally use “Typical”– Maintainers (government or contractor)– Training– Working environment & conditions– Equipment & tools– Manuals– Spares & consumables

RM&A Measures

Availability Measures• Operational Availability (Ao) can be described by the

following equation: Ao=uptime/total time.

Operating Time + Standby TimeOperating Time + Standby Time + TPM + TCM + MLDT

TPM = Total Preventive Maintenance TimeTCM = Total Corrective Maintenance TimeMLDT = Mean Logistics Delay Time


RM&A Measures

Availability Measures• Operational Availability (Ao) can be described by the following equation: Ao=uptime/total time.

Operating Time + Standby TimeOperating Time + Standby Time + TPM + TCM +

MLDT

TPM = Total Preventive Maintenance TimeTCM = Total Corrective Maintenance TimeMLDT = Mean Logistics Delay Time


RM&A Measures

Availability Measures• Inherent Availability (Ai) - When only

reliability and corrective maintenance or repair (i.e., design) effects are considered. This level of availability is solely a function of the inherent design characteristics of the system.*

• Poor estimate of combat/field availability since it ignores standby and delay times and assumes 100% efficiency

• Ai = MTBF / (MTBF + MTTR)

* U.S. Army TM 5-698-1, 19 JANUARY 2007, Para 1-6a Page 1-3

RM&A Measures

Availability Measures• Materiel Availability (Am) is a measure of the percentage of

the total inventory of a system operationally capable (ready for tasking) of performing an assigned mission at a given time, based on materiel condition. This measure can be expressed mathematically as number of operational end items/total population.*

* JCIDS Manual 12 February 2015 App D, Encl D Para 3.c.(1)(a)

RM&A Measures

• Beware the pros and cons of your metrics. For example

• Ao – Can you contract for that?• Ai – You can contract for it, but

does the user care?• MTBF vs MTBEFF or MTBSA

or… does it matter?• Mission Reliability versus

Logistics Reliability

Availability Terminology

• TCM = Total Corrective Maintenance Time

• TPM = Total Preventive Maintenance Time

• TCM + TPM = TMT (Total Maintenance Time)

• ALDT = Administrative / Logistics Down Time (or Delay Time)

• TDT (Total Down Time) = TMT + ALDT

Availability Terminology (cont.)

• OT = Operating Time (equipment in use)

• ST = Standby Time (not operating, butassumed operable)

• UT (Up Time) = OT + ST(UT = Total intended utilization period)

Breakdown of System Time

TotalTime

OffTime

UpTime

Total DownTime

ActiveMaint

Admin &Logistics

Down Time

OperatingTime

StandbyTime

TCM TPM

Availability Mini Exercise• A system requires an operational availability of 0.8. The

system is to be available for operation 24 hours a day, 5 days a week. PM for the system is 5 hours/week.

• The system was tested during a 30 calendar day period. • The following data was collected:

• Operating Time (OT) = 8 hours/day

• Failures = 15

• Total Corrective Maintenance (TCM) = 60 hours

• Time Spent Awaiting Parts = 25 hours

• Administrative time getting tools & supplies = 10 hours

1. Did the system meet the Ao requirements?

2. What assumptions did you make?

Availability Mini Exercise• Team 1 = The Prime Contractor• Team 2 = The PM• Team 3 = The User/Capability Sponsor• Team 4 = The Operational Test Agency• Team 5 = 60 Minutes• Take 15 minutes and compute your Ao and document

your assumptions

RM&A Summary• Discussed with regard to

Reliability/Reliability Growth, Maintainability and Availability– Fundamentals– Measures/Metrics– Key Characteristics– Risks and Constraints

• Bottom Line– RM&A are crucial to life cycle cost– RM&A are combat multipliers– RM&A require extensive planning and resources– Lots of statistics – be careful

maintainability and availability · 2015. 4. 28. · rm&a measures maintainability measures •...

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