Question

The following information is known for a given system:

1. The total System Operating time for a designated period is 10,000 hours

2. The corrective maintenance rate is .004 maintenance action per hour of system operation

3. The perventive maintenance rate is .001 maintenance action per hour of system operation

4. The average downtime per maintenance action is 50 hours with a mean downtime of 5 hours for corrective maintenance

a. Calculate the following: MTBF, MTBM, Ai, Ao?

b. What is the relability for 100 hours of operation

c. Assume that the operational availability requirement for the system is .8. Lets say that the actual demonstrated MTBM is 100 hour which is less than the calculated value above. Given this condition, what is the new Ao value? What corrective action action needs to be taken to maintain mission availability requirements (in other words retain an Ao value of .80)?

Answer 1

a) Total Operation time =10000 hrs

Corrective maintenance rate/ hour = 0.004

No of corrective maintenance in 10000 hurs = 0.004*10000= 40

so number of failures in total operation hours = 40 (as corrective maintenece needed after failure)

Preventive manitenenace rate /hour = 0.001

No of corrective maintenance = 0.001*10000= 10

Total number of maintenace = 40+10 =50

Mean time between failures(MTBF) = = 1/0.004 = 250 hours

Down time for corrective maintenance = mean downtime for corrective maintenance* (number of corrective maintenace) = 5*40 = 200

Downtime per preventive maintenace = total downtime/maintenance - mean downtime/ corrective maintenance =50-5 = 45 hours

So total down time for preventive maintenace = 45*10 = 450 hours

Total downtime = 450+200 = 650 hours

Up time = 10000-650 = 9350 hours

MTBM = = 9350/ 50 =187hours

MTTR = Totaal down time /No of breakdown = 650/40= 16.25 hours

Ai= MTBF/(MTBF+MTTR) = 250/(250+16.25) = 0.939

Ao = MTBM/(MTBM+MDT) = 187/(187+50) = 0.789

b) Reliability for 100 hours of operation = = = 0.67

c)

MTBM= 100

MDT= 50

Ao = 100/(100+50 )= 0.66

To incraese the Ao value we need to decerease the MDT(meand down time )