maintainability and availability · 2015. 4. 28. · rm&a measures maintainability measures •...
TRANSCRIPT
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. *
* Army Regulation 702–19 “Reliability, Availability, and Maintainability” dated 28 April 2015 Pg 24
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
* Army Regulation 702–19 “Reliability, Availability, and Maintainability” dated 28 April 2015 Pg 23
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.*
* Army Regulation 702–19 “Reliability, Availability, and Maintainability” dated 28 April 2015 Pg 24
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
* Army Regulation 702–19 “Reliability, Availability, and Maintainability” dated 28 April 2015 Pg 24
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
* Army Regulation 702–19 “Reliability, Availability, and Maintainability” dated 28 April 2015 Pg 24
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