1 / 52

Systems Availability Concepts & Metrics

Systems Engineering Program. Department of Engineering Management, Information and Systems. EMIS 7305: Systems Reliability, Supportability and Availability Analysis. Systems Availability Concepts & Metrics. In Work. Dr. Jerrell T. Stracener, SAE Fellow. Concept of a System.

shilah
Download Presentation

Systems Availability Concepts & Metrics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Systems Engineering Program Department of Engineering Management, Information and Systems EMIS 7305: Systems Reliability, Supportability and Availability Analysis Systems Availability Concepts & Metrics In Work Dr. Jerrell T. Stracener, SAE Fellow

  2. Concept of a System A system is defined as an aggregation or assemblage of objects joined in some regular interaction or interdependence, principally dynamic with changes over time. Systems are generally characterized by Entities, Attributes, and Activities Examples: System Entities Attributes Activities Traffic Flow Cars Speed, Distance Driving, Delays Bank Operators Customers Balance, Credit Status Withdrawing, Depositing Communications Messages Length, Priority Transmitting, Receiving Supermarket Customers Shopping List Shopping, Checkout Stock Levels Aircraft Systems and R/M/S Flying, Inspection, Subsystems Availability/Cost Combat, Maintenance

  3. Fossil Fuel Power Plant System 2 3 1 Turbine Boiler Generator 4 Condenser 7 6 5 Circulating WaterSystem Feed waterSystem CondensateSystem 8 Auxiliaries

  4. System Cost TechnicalRisk MilitaryUtility SortieRate Targetsat Risk Effectiveness Availability Survivability

  5. Cost Development Production Support Technology Airframe Systems Personnel Engine Cost perUnit Cost perShipset Maintenance Airframe Number ofUnits Number ofShipsets Fuel Systems SFC Testing Flight Hours

  6. TechnicalRisk Attainability Consequences Maturity Complexity Dependency Performance Hardware Hardware Performance Schedule Software Software Schedule Cost

  7. Targetsat Risk PayloadWeight Deployability CombatRadius Ferry Range RunwayRequired

  8. Effectiveness Attacks perSortie Kills perAttack WeaponEnvelope TargetAcquisition Weapons perKill WeaponsLoad SearchVolume Lethality TargetDetection Accuracy TargetIdentification DiveDelivery LevelDelivery LoftDelivery NonautonomousDelivery

  9. Availability Reliability Maintainability Serviceability Component MMH/FH Turn AroundTime Subsystems Downtime/FH Battle DamageRepair Mean TaskTimes MTBM-1

  10. Survivability Detectability Avoidability Vulnerability Air-to-AirWeapon RF Redundancy Agility Non-LethalCountermeasure IR Location Speed/Altitude Electronic EO/Visual Shielding Maneuver Chaff Acoustic Passive WingLoading WarningReceivers EME Active Thrust/Weight Decoys

  11. System Performance Measures • Availability: A measure of the degree to which an item is in an operable state at the start of a mission when the mission is called for at a random time. Expressed as inherent, achieved, or operational. • Readiness: The probability that military forces, units, weapons systems, equipment and personnel will be capable of undertaking the mission and function for which they are designed or organized, at any random point in time. • Sustainablity The capability of military forces, units, equipments and personnel to maintain a specified level of mission activities for specified times.

  12. Availability Analysis Flow Diagram • Mission Reliability • MTBF • MTBM Reliability Analysis Availability Analysis Cost EffectivenessAnalysis Maintainability Analysis • MTTR • MDT (A) • MDT (L) Supportability Analysis Life Cycle CostAnalysis

  13. System Time Relationships TotalTime InactiveTime ActiveTime DownTime UpTime Corrective Maintenance Time MaintenanceTime Not OperatingTime Preventive Maintenance Time ModificationTime AlertTime DelayTime Supply DelayTime ReactionTime Time to RestoreFunctionsDuring Missions Administrative Delay Time MissionTime

  14. A/C Time Breakdown Availability Analysis Period of Interest Total Off Time Total System Operating Time Total Up Time Total Down Time Administrative/ Logistics Delay Time Active Maintenance Time Standby Time Operating Time P C TCM TPM

  15. Availability (Operational Readiness) “The Probability that at any point in time the system is either operating satisfactorily or ready to be placed in operation on demand when used under stated conditions.”

  16. System Operational Parameters • Operational Effectiveness • Readiness or Availability • Mission Success • Ownership Cost • Logistic Support Cost • Operating Cost

  17. Operational Concept Support Concept Maintenance Concept The System View • Availability • Sortie Generation Rates • Basing Product • Reliability • Maintainability • Supportability • Testability • Organization • Requirements • Schedule Maintenance • Unscheduled Maintenance • Spares • Technical Publications • Training • Support Equipment

  18. Reliability & Maintainability Relationships ConfigurationComplexityStress AccessConfigurationComplexityAvailability Reliability Design AccessConfigurationComplexity AccessConfigurationComplexity Maintainability

  19. Requirements ReliabilityMaintainabilitySupportability Effectivenessand Availability Design Life Cycle Cost Reliability, Maintainability & Supportability Systems Operation Performance

  20. Inherent (Intrinsic) Availability • Probability that a system or equipment shall operate satisfactorily at any given time when used under stated conditions, without consideration for any schedule or preventive maintenance, in an ideal support environment. • Refers primarily to the built-in capability of the system or equipment – function of repair times and failure frequency • No defect may or may not be included depending upon ground rules.

  21. Operational Availability • Probability that a system or equipment shall operate satisfactorily at any given time (When used under stated conditions?) • Measure of total capacity – function of repair times, failure frequency, preventive and scheduled maintenance, supply downtime, administrative down time, support equipment downtime, …

  22. Types of Availability Estimates • Point Estimate – single, average or “mean value” of availability characteristic • Interval Estimate – confidence that availability is within a specified range of values (with a certain probability) • Instantaneous Estimate – availability measure value at a particular point in time • Special Cases of field system reliability/availability estimates: • Apparent Availability – availability of a system calculated considering detected failures only • Real Availability – availability of a system considering all system failures

  23. Availability Definition • Easy to understand • Difficult to compute • Uptime and downtime are difficult to define • Steady state value

  24. Types of Availability • Inherent Availability (Ai): • The designed in availability. Ai calculations ignore all logistics contributions to downtime.

  25. Types of Availability • Operational Availability (A0): • The expected in-service availability. A0 calculations include the impact of logistics on availability. Exactly which logistics elements are included must be defined in advance.

  26. R&M Trade-offs (typical) Maintainability (MTTR in hours) 120 100 80 60 40 20 A=0.984 A=0.995 Maximum A=0.999 2000 4000 6000 8000 10000 Min Reliability (MTBF in hours)

  27. E1 l, m Inherent Availability • Single Element with constant failure rate l and constant repair (restore) rate m- Instantaneous Inherent Availability- Steady State Inherent AvailabilityWhere

  28. E2 E1 E1 E2 En l, m l, m ... ... l1, m1 l2, m2 ... ... ln, mn Inherent Availability • Series Reliability Configuration with two Elements- Steady State Inherent Availability • Series Reliability Configuration with n Elements- Steady State Inherent Availability

  29. E1 E2 Inherent Instantaneous Availability • Two Element active parallel reliability configuration - Instantaneous Inherent Availability l, m l, m

  30. Inherent Instantaneous Availability WhereSteady State Inherent Availability

  31. E1 E2 En Inherent Steady State Availability • Active Parallel Reliability Configuration with n Elements l1, m1 l2, m2 ... ... ln, mn

  32. E1 E2 Inherent Steady State Availability • Standby Configuration with Two Elements l, m l, m - Inherent Steady State Availability

  33. Operational Readiness (OR) Definition Operational Readiness (OR) is defined by the Navy to be a condition status indicating an operational unit aircraft to be safely flyable and capable of performing one or more (but not necessarily all) of the primary missions of the unit to which assigned.

  34. Availability Analysis provides a mathematical basis for evaluating system design and development decisions based on system level performance measures in order to influence the air vehicle design concurrently with support system design.

  35. Aircraft Operational Availability (AO) Definition Aircraft operation availability AO is defined to be the probability that the aircraft is in an operable and committable state at a random point in time when used in a typical maintenance and supply environment. The downtime expected under wartime conditions (allowing for long term deferral of some maintenance) is determined from estimates of the rates of “essential: unscheduled maintenance actions (UMA’s) and “essential” removals.

  36. Availability, Reliability, Maintainability 1 MTBF Operational State Failed State 1 MTTR

  37. Major Factor Influencing Availability • System Reliability Design Characteristics • MTBF: a reliability function which assumes that operation occurs after early failure (infant mortality) and prior to war-out, i.e., a constant failure rate exists. • MTBMA: Mean Time Between Maintenance Actions - a reliability function which accounts for all causes of maintenance activity, whether a failure occurred or not.

  38. Major Factor Influencing Availability • System Maintainability Design Characteristics • Mean Time To Repair (MTTR): a maintenance function, includes corrective maintenance time (CMT) and preventive maintenance time (PMT) • Support System Design Characteristics • Mean Logistics Down Time (MLDT): a maintenance related logistics function which involves spares provisioning and logistics delay time (LDT) administrative delay time (ADT)

  39. Major Factor Influencing Availability • System Maintainability Design Characteristics • MTTR: a maintenance function, includes corrective maintenance time (CMT) and preventive maintenance time (PMT) • Support System Design Characteristics • Mean Logistics Down Time: a maintenance related logistics function which involves spares provisioning and logistics delay time (LDT) administrative delay time (ADT)

  40. Major Availability Analysis Process Elements • Reliability Analysis Techniques (typical) • Failure Modes and Effects Analysis • Failure Modes and Effects Criticality Analysis • Reliability Block Diagrams • Failure Rate Estimation • Maintainability Analysis Techniques (typical) • Maintenance Task Time Analysis • Engineering scale models

  41. Major Availability Analysis Process Elements • Supportability Elements (typical) • Logistics Support Analysis • Spares Provisioning Levels

  42. Maintenance Events Drivers 67% 15 14 14 12 12 MaintenanceEvents, % Landing Gear FlightControls Propulsion Airframe Avionics Aircraft Systems

  43. Typical A/R Model Applications • Overall Requirements Calibration • ECP Evaluation • Trade Studies on R&M • Wide Range of Sensitivity Analysis • Manpower Requirements Derivation • LRU Spares/Not Mission Capable due to Spares (NMCS) Evaluation • Flying Hour Program Evaluation • Sequential vs Parallel Maintenance Options • Formal Support System Evaluation

More Related