1. Stracener_EMIS 7305/5305_Spr08_04.22.08 1 System Availability Modeling & Analysis Case Studies 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

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3. Stracener_EMIS 7305/5305_Spr08_04.22.08 3 Aircraft Availability Model Logic Initiate Scenario Fly Mission Profile Ready Aircraft Available? Substitute Available? Repair and Return to Ready Pool In-Flight Gripe? Defect? Repair On Aircraft? Spare Available? Trouble Shoot @ 2-Digit WUC Level Service and Turnaround Aircraft Perform Repair MTL/EMT/MM Wait for Spare Repair Item Remove Item Replace Unit and Check Out Yes No Yes No

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22. Stracener_EMIS 7305/5305_Spr08_04.22.08 22 Blue Flame Aircraft Case Study

23. Stracener_EMIS 7305/5305_Spr08_04.22.08 23 Blue Flame Availability Analysis Previous availability & support system analysis applications (heritage) Review of Blue Flame Requirements and system/subsystem characteristics Determination of radar component of Blue Flame availability Development of Blue Flame radar availability model Calculation of Blue Flame radar baseline availability estimates

24. Stracener_EMIS 7305/5305_Spr08_04.22.08 24 Blue Flame Analysis Working Definitions System Reliability Design Characteristics –Mean-Time-Between-Failure (MTBF)-a reliability function which assumes that operation occurs after early failure (infant mortality) and prior to wear-out, I.e., a constant failure rate exists. –Mean-Time-Between-Maintenance-Actions (MTBMA)-a reliability function which accounts for all causes of maintenance activity, whether a failure occurred or not. System Maintainability Design Characteristics –Mean-Time-To-Repair (MTTR)-a maintenance function, can include 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) and administrative delay time (ADT) Operational Availability (Ao)- the degree to which an item (the radar set) is in an operable and committable state at the start of a mission when the mission is called for at a random time.

25. Stracener_EMIS 7305/5305_Spr08_04.22.08 25 Blue Flame Operational Availability Inherent Availability (Ai) A i = Achieved Availability (Aa) A a = Operational Availability (Ao) MTBF MTBF + MTTR(CMT) MTBF MTBF + MTTR MTBF MTBF + MTTR + MLDT Ao =

26. Stracener_EMIS 7305/5305_Spr08_04.22.08 26 Blue Flame Fleet Requirements Fleet Requirements –Operational Availability -- 95% –Sortie Rate --12/PAA/Mo (Peacetime) –Mission Reliability --93% (High Mission) --96% (Low Mission) Fleet Operational Data –3.5 flying hrs/high mission --50% of missions –1.5 flying hrs/low mission --50% of missions –500 aircraft -- one radar set per aircraft –10 bases -- 50 aircraft per base –1.5 to 1 ratio of operating hours to flying hours –Radar set has 80% duty cycle relative to aircraft operating hours –Average of 30 flying hours per aircraft per month –20 year field use period for each radar system

27. Stracener_EMIS 7305/5305_Spr08_04.22.08 27 Blue Flame Radar Support Characteristics Maintenance/Logistics Concept –Organizational --Remove/Replace LRUs on aircraft (10 sites) –Intermediate -- Remove/Replace SRUs at shop (10 sites) –Depot -- Repair SRUs (1CONUS site) Sparing Concept --Intermediate (LRU & SRU) --Depot (SRU & Piece Parts only) Built-in Test Capability --Fault isolation to faulty LRU @90% --Fault isolation to faulty SRU @90% --Fault detection @ 2% Support Equipment -Organizational -- None -Intermediate -- Simple PSGE -Depot --ATE All LRUs and SRUs are repairable

28. Stracener_EMIS 7305/5305_Spr08_04.22.08 28 Blue Flame R&M Requirements Aircraft MTBM 4.0 hrs. Aircraft MMH/FH (unscheduled) 3.0 hrs. Aircraft MMH/FH (scheduled) 0.5 hrs. Radar MTBM 20.0 hrs. Radar MMH/FH 0.5 hrs. Radar Failure Rate Allocation Antenna/Receiver LRU 16,667 failures/10x6 hrs Transmitter LRU 20,000 failures/10x6 hrs Processor LRU 10,000 failures/10x6 hrs Displays/Controls LRU 2,500 failures/10x6 hrs Power Supply LRU 883 failures/10x6 hrs Radar MTTRs & Scheduled Maintenance Organizational level MTTR 0.5 hrs Intermediate level MTTR 2.5 hrs Depot level MTTR 6.0 hrs XMTR Magnetron replacement: Every 1000 flying hrs, 1 person,4.0 hrs.

29. Stracener_EMIS 7305/5305_Spr08_04.22.08 29 Miscellaneous Blue Flame Characteristics Spares turnaround time (TAT) –Intermediate level --75 days –Depot level -- 45 days Constant failure rate assumed Re-test OK(RTOK) rate –Intermediate level -- 20% –Depot level -- 8% Learning curve on maintenance -- 90% One set PGSE per base Depot ATE availability -- 80% Ave. administrative delay time -- 0.75 hrs./repair Ave. logistics delay time -- 6.6 hrs./repair 90% probability of spare in 2.0 hrs. 10% probability of no spare in 48 hrs.

30. Stracener_EMIS 7305/5305_Spr08_04.22.08 30 Blue Flame Aircraft system Elements WBS Level 0 –Blue Flame Aircraft WBS Level 1-Major Systems Airframe Flight Controls Navigation Propulsion Radar WBS Level 2-Subsystems (Radar) Antenna/Receiver Transmitter Processor Display/Controls Power Supply

31. Stracener_EMIS 7305/5305_Spr08_04.22.08 31 Blue Flame Tradeoff Analyses Design Tradeoffs Baseline -- single transmitter Alternate -- redundant transmitters (2) – operating redundancy Support Tradeoffs Baseline -- 90% spares assurance Alternate -- 80% spares assurance The big question before the house is: Where do we start?

32. Stracener_EMIS 7305/5305_Spr08_04.22.08 32 Review the ‘Blue Flame Case Study’ excel spreadsheet and check/verify the availability numbers corresponding to a single transmitter on the next page and show the results of your analysis. Blue Flame Aircraft Radar Availability – Case Study

33. Stracener_EMIS 7305/5305_Spr08_04.22.08 33 Radar Availability at stated Spares Level Design Option90% Spares80% Spares Single Transmitter65%55% Radar Trade Result Summary

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40. Stracener_EMIS 7305/5305_Spr08_04.22.08 40 The formula for operational availability, A o, is: Therefore we need to obtain only the values of the following terms to evaluate A o : MTBMA MTTR(CMT) MTTR(PMT) MTTR(LDT) MTTR(ADT) Blue Flame Aircraft Radar Availability Solution

41. Stracener_EMIS 7305/5305_Spr08_04.22.08 41 90% Spares: From the given data for a single transmitter, we get: Total Radar Maintenance Action = MTBMA = 20 hours MTTR(CMT) = 0.5 hours (Organizational Level) MTTR(PMT) = 4 hours (Radar Transmitter Magnetron R/R time) MLDT(ADT) = 0.75 hours MLDT(LDT) = 0.9*2 + 0.1*48 = 6.6 hours Since the probability of spare in 2 hours = 90% and the probability of spare in 48 hours = 10% Plugging these numbers into the formula for A o gives us: Therefore A o = 0.628 = 62.8% Blue Flame Aircraft Radar Availability Solution

42. Stracener_EMIS 7305/5305_Spr08_04.22.08 42 80% Spares: All the data is the same as for 90% spares, except for: MLDT(LDT) = 0.8*2 + 0.2*48 = 11.2 hours Since the probability of spare in 2 hours = 80% and the probability of spare in 48 hours = 20% Table for comparison of values: 90% Spares80% Spares Given Value 65% 55% Calculated Value 62.8% 54.9% Blue Flame Aircraft Radar Availability Solution