1. Stracener_EMIS 7305/5305_Spr08_04.17.08 Systems Availability Modeling & Analysis Dr. Jerrell T. Stracener, SAE Fellow Leadership in Engineering EMIS 7305/5305 Systems Reliability, Supportability and Availability Analysis Systems Engineering Program Department of Engineering Management, Information and Systems

2. Stracener_EMIS 7305/5305_Spr08_04.17.08 2 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.

3. Stracener_EMIS 7305/5305_Spr08_04.17.08 3 System Operational Parameters  Operational Effectiveness Readiness or Availability Mission Success  Ownership Cost Logistic Support Cost Operating Cost

4. Stracener_EMIS 7305/5305_Spr08_04.17.08 4 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.”

5. Stracener_EMIS 7305/5305_Spr08_04.17.08 5 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.

6. Stracener_EMIS 7305/5305_Spr08_04.17.08 6 Availability Definition Easy to understand Difficult to compute Uptime and downtime are difficult to define Steady state value

7. Stracener_EMIS 7305/5305_Spr08_04.17.08 7 Availability, Reliability, Maintainability Failed State Operational State 1 MTBF 1 MTTR

8. Stracener_EMIS 7305/5305_Spr08_04.17.08 8 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.

9. Stracener_EMIS 7305/5305_Spr08_04.17.08 9 Types of Availability Inherent Availability (A i ): –The designed in availability. A i calculations ignore all logistics contributions to downtime.

10. Stracener_EMIS 7305/5305_Spr08_04.17.08 10 R&M Trade-offs (typical) 120 100 80 60 40 20 Maintainability (MTTR in hours) 2000 4000 6000 8000 10000 Maximum A=0.995 Min Reliability (MTBF in hours) A=0.984 A=0.999

11. Stracener_EMIS 7305/5305_Spr08_04.17.08 11 Single Element with constant failure rate and constant repair (restore) rate  - Instantaneous Inherent Availability - Steady State Inherent Availability Where Inherent Availability E1E1 

12. Stracener_EMIS 7305/5305_Spr08_04.17.08 12 Inherent Availability Series Reliability Configuration with two Elements - Steady State Inherent Availability E1E1  E2E2 E1E1    E2E2    EnEn n  n  Series Reliability Configuration with n Elements - Steady State Inherent Availability

13. Stracener_EMIS 7305/5305_Spr08_04.17.08 13 Two Element active parallel reliability configuration - Instantaneous Inherent Availability E1E1 E2E2  Inherent Instantaneous Availability

14. Stracener_EMIS 7305/5305_Spr08_04.17.08 14 Where Steady State Inherent Availability Inherent Instantaneous Availability

15. Stracener_EMIS 7305/5305_Spr08_04.17.08 15 Active Parallel Reliability Configuration with n Elements E1E1 E2E2       EnEn n  n  Inherent Steady State Availability

16. Stracener_EMIS 7305/5305_Spr08_04.17.08 16 Standby Configuration with Two Elements E1E1 E2E2  Inherent Steady State Availability - Inherent Steady State Availability

17. Stracener_EMIS 7305/5305_Spr08_04.17.08 17 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, …

18. Stracener_EMIS 7305/5305_Spr08_04.17.08 18 Aircraft Operational Availability (A O ) Definition Aircraft operation availability A O 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.

19. Stracener_EMIS 7305/5305_Spr08_04.17.08 19 Types of Availability Operational Availability (A 0 ): –The expected in-service availability. A 0 calculations include the impact of logistics on availability. Exactly which logistics elements are included must be defined in advance.

20. Stracener_EMIS 7305/5305_Spr08_04.17.08 20 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

21. Stracener_EMIS 7305/5305_Spr08_04.17.08 21 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.

22. Stracener_EMIS 7305/5305_Spr08_04.17.08 22 The System View Product Spares Technical Publications Training Support Equipment Availability Sortie Generation Rates Basing Reliability Maintainability Supportability Testability Organization Requirements Schedule Maintenance Unscheduled Maintenance Operational Concept Maintenance Concept Support Concept

23. Stracener_EMIS 7305/5305_Spr08_04.17.08 23 System Time Relationships Maintenance Time Modification Time Delay Time Corrective Maintenance Time Preventive Maintenance Time Supply Delay Time Administrative Delay Time Inactive Time Down Time Total Time Active Time Up Time Alert Time Not Operating Time Reaction Time Mission Time Time to Restore Functions During Missions

24. Stracener_EMIS 7305/5305_Spr08_04.17.08 24 A/C Time Breakdown Availability Analysis Period of Interest Total Off Time Operating Time Standby Time Total Up TimeTotal Down Time Total System Operating Time TCM TPM Active Maintenance Time Administrative/ Logistics Delay Time C P

25. Stracener_EMIS 7305/5305_Spr08_04.17.08 25 Availability Analysis Flow Diagram Mission Reliability MTBF MTBM Reliability Analysis Availability Analysis MTTR Maintainability Analysis Cost Effectiveness Analysis MDT (A) MDT (L) Supportability Analysis Life Cycle Cost Analysis

26. Stracener_EMIS 7305/5305_Spr08_04.17.08 26 Reliability & Maintainability Relationships DesignReliability Maintainability Configuration Complexity Stress Access Configuration Complexity Access Configuration Complexity Availability

27. Stracener_EMIS 7305/5305_Spr08_04.17.08 27 Reliability, Maintainability & Supportability Requirements Systems Operation Performance Reliability Maintainability Supportability Effectiveness and Availability Life Cycle Cost Design

28. Stracener_EMIS 7305/5305_Spr08_04.17.08 28 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.

29. Stracener_EMIS 7305/5305_Spr08_04.17.08 29 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)

30. Stracener_EMIS 7305/5305_Spr08_04.17.08 30 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)

31. Stracener_EMIS 7305/5305_Spr08_04.17.08 31 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

32. Stracener_EMIS 7305/5305_Spr08_04.17.08 32 Major Availability Analysis Process Elements Supportability Elements (typical) –Logistics Support Analysis –Spares Provisioning Levels

33. Stracener_EMIS 7305/5305_Spr08_04.17.08 33 Maintenance Events Drivers PropulsionAirframe Landing Gear Avionics Flight Controls 15 14 12 Aircraft Systems Maintenance Events, % 67%

34. Stracener_EMIS 7305/5305_Spr08_04.17.08 34 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

35. Stracener_EMIS 7305/5305_Spr08_04.17.08 35 Availability/Readiness (A/R) Model Example Analysis Results

36. Stracener_EMIS 7305/5305_Spr08_04.17.08 36 Availability/Readiness (A/R) Model Example Analysis Results

37. Stracener_EMIS 7305/5305_Spr08_04.17.08 37 Availability/Readiness (A/R) Model Example Analysis Results

38. Stracener_EMIS 7305/5305_Spr08_04.17.08 38 Availability/Readiness (A/R) Model Example Analysis Results

39. Stracener_EMIS 7305/5305_Spr08_04.17.08 39 Availability/Readiness (A/R) Model Example Analysis Results

40. Stracener_EMIS 7305/5305_Spr08_04.17.08 40 Unclassified Availability/Readiness (A/R) Model Example Analysis Results

41. Stracener_EMIS 7305/5305_Spr08_04.17.08 41 Availability/Readiness (A/R) Model Example Analysis Results

42. Stracener_EMIS 7305/5305_Spr08_04.17.08 42 Availability/Readiness (A/R) Model Example Analysis Results

43. Stracener_EMIS 7305/5305_Spr08_04.17.08 43 Availability/Readiness (A/R) Model Example Analysis Results