Stracener_EMIS 7305/5305_Spr08_04.22.08 1 System Availability Modeling & Analysis Case Studies Dr. Jerrell T. Stracener, SAE Fellow Leadership in Engineering

Stracener_EMIS 7305/5305_Spr08_04.22.08

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System Availability Modeling & AnalysisCase Studies

Dr. Jerrell T. Stracener, SAE Fellow

Leadership in Engineering

EMIS 7305/5305Systems Reliability, Supportability and Availability Analysis

Systems Engineering ProgramDepartment of Engineering Management, Information and Systems


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Aircraft Availability Analysis


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Aircraft Availability Model Logic

InitiateScenario Fly Mission

Profile

ReadyAircraft

Available?

SubstituteAvailable?

Repair andReturn to Ready

Pool

In-FlightGripe?

Defect?

Repair OnAircraft?

SpareAvailable?

Trouble Shoot @2-Digit WUC Level

Service andTurnaround Aircraft

Perform RepairMTL/EMT/MM

Wait for Spare Repair Item

Remove ItemReplace Unit

and Check Out

Yes

No

Yes

Yes

Yes

Yes

Yes

No

No

No

No

No


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Blue Flame Aircraft Case Study


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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


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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.


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Blue Flame Operational Availability• Inherent Availability (Ai)

Ai =

• Achieved Availability (Aa)

Aa =

• Operational Availability (Ao)

MTBF

MTBF + MTTR(CMT)

MTBF

MTBF + MTTR

MTBF

MTBF + MTTR + MLDTAo =


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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

R M S A


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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


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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.


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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.


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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


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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?


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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


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Radar Availability at stated Spares Level

Design Option 90% Spares 80% Spares

Single Transmitter 65% 55%

Radar Trade Result Summary


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The formula for operational availability, Ao, is:

Therefore we need to obtain only the values of the following terms to evaluate Ao:

MTBMAMTTR(CMT)MTTR(PMT)MTTR(LDT)MTTR(ADT)

Blue Flame Aircraft Radar Availability Solution

MLDT(ADT) MLDT(LDT) MTTR(PMT) MTTR(CMT) MTBMA

MTBMAA0


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90% Spares:

From the given data for a single transmitter, we get:Total Radar Maintenance Action = MTBMA = 20 hoursMTTR(CMT) = 0.5 hours (Organizational Level)MTTR(PMT) = 4 hours (Radar Transmitter Magnetron R/R time)MLDT(ADT) = 0.75 hoursMLDT(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 Ao gives us:

Therefore Ao = 0.628 = 62.8%


628.085.31

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75.06.645.002

20Ao


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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% Spares 80% Spares

Given Value 65% 55%Calculated Value 62.8% 54.9%


%9.54549.045.36

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75.02.1145.002

20Ao

Documents

Stracener_EMIS 7305/5305_Spr08_04.22.08 1 System Availability Modeling & Analysis Case Studies Dr. Jerrell T. Stracener, SAE Fellow Leadership in Engineering