Question

Q.5

In defining the detailed maintenance plan and establishing criteria for equipment design (and system support),it is necessary to determine whether it is economicy feasible to repair certain assemblies or to discard them when failures occur. If the decision is to accomplish repair, it is appropriate to determine the maintenance level at which the repair should be accomplished (i.e., intermediate level maintenance or depot level maintenance). For the purposes of this exercise, Assembly A-1 (one of 15 assemblies in Unit B of system XYZ) is to be evaluated in terms of the three options. The following information is provided to facilitate the evaluation of the decision

System XYZ is installed in each of 60 aircraft that are deployed at five operational bases over an 8-year period. System XYZ will be utilized on an average of 4 hours per day, 365 days per year, and the total system operating time is 452,600 hours.

System XYZ is packaged in three units: Unit A, Unit B, and Unit C. When corrective maintenance is required , a built-in self-test capability enables rapid checkout and fault isolation to the unit level. In the event of a no-go or failure condition, the applicable unit is re­moved and replaced with a spare. The faulty removed unit is sent to the intermediate-level maintenance shop (located at the operational base) for corrective maintenance. Unit repair is accomplished through fault isolation to the applicable assembly (e.g., Assembly A-1), removal of the faulty assembly and replacement with a spare, and checkout of the unit to verify satisfactory operation.The faulty assembly must now be processed in accor­ dance with the designated maintenance plan.

Pertinent data associated with Assembly A-1 are noted below.

a. The estimated acquisition cost for Assembly A-1 (to include design and develop­ ment cost and production cost) is $1700 if the assembly is designed to be repairable, and $1600 if the assembly is designed to be discarded at failure.

b. The estimated failure rate (or corrective maintenance rate) is 0.00045 failure per hour of system operation.

c. When failures occur, repair is accomplished by one technician assigned on a full­ time basis (i.e.,for the duration of the predicted elapsed active repair time). The estimated Mct is 3 hours. The labor rate is $20 per labor-hour for intermediate maintenance and $30 per labor-hour for depot maintenance.

d. Supply support involves three categories of cost: (1) the cost of spare assemblies in the pipeline, (2) the cost of spare components to enable the repair of faulty assemblies, and (3) the cost of inventory maintenance. Assume that five spare assemblies will be required in the pipeline when maintenance is accomplished at the intermedi­ate level, and that 10 spares will be required when maintenance is accomplished at the depot level. For component spares, assume a material cost of $50 per maintenance action. The estimated cost of inventory maintenance will be 20% of the in­ ventory value.

e. When assembly repair is accomplished , special test and support equipment is required for fault diagnosis and checkout. The cost per set is $12,000, which includes acquisition cost and runortized maintenance cost.

f. Transportation and handling cost is considered to be negligible when maintenance is accomplished at the intermediate level; however, assembly maintenance accom­plished at the depot level will involve an extensive runount of transportation. For depot maintenance, assume $150 per 100 pounds per one-way trip (independent of the distance), and that the packaged assembly weighs 20 pounds.

g. The allocation for Assembly A-1 relative to maintenance facility cost is categorized in terms of (1) an initial fixed cost, and (2) a sustaining recurring cost proportional to facility use requirements. The initial fixed cost is $1000 per installation, and the assumed usage cost allocation is $1.00 per direct maintenance labor-hour at the in­ termediate level and $1.50 per direct maintenance labor-hour at the depot level.

h. Technical data requirements will constitute (1) the maintenance instructions to be included in the technical manual to support assembly repair activities and (2) the failure reporting and maintenance data covering each maintenance action in the field. Assume that the cost for preparing and distributing maintenance instructions is $1000 and that the cost for field maintenance data is $25 per maintenance action.

i. There will be some initial formal training costs associated with maintenance personnel when the assembly repair option is considered. Assume 30 student-days of formal training for intermediate-level maintenance and 6 student-days for depot-level maintenance. The cost of training is $150 per student-day.

j. As a result of maintenance actions, there will be a requirement for the disposal of ei­ther faulty assemblies or faulty components. The assumed disposal cost is $20 per assembly and $2 per component.

Evaluate Assembly A-1 (based on the information provid­ed previously) and make a recommendation. Should Assembly A-1 be repaired at the intermediate level of maintenance, repaired at the depot level of maintenance, or discarded at failure? Show the cost for each of the cost results for each of the the three strategies as a result of the conditions above. use this work sheet to conduct the evualuation. Select the strategy that yields the lowest cost for assembly A-1

Answer 1

the best option is to select discard at failure because it has the lowest cost as explained below.

Total system operating time=452600

Estimated failure rate = .00045

Total failure=.00045*452600=203.67

Per unit assembly disposal cost=20

Total disposal cost=20*203.67=4073.4$

1.For discarded at failure option total cost incurred is given below

Total assembly cost =1600*203.67=325872

Total assembly cost+ Total disposal cost=325872+4073.4=329945.4$

2.For Maintenance at intermediate level

Total assembly repair cost=392845.46 $

3.For Maintenance at Depot level

Total assembly repair cost=813184.565 $

Detailed calculation is shown in excel table below