A large copper mine in Chile operates a fleet of 49 large haul trucks. The trucks employ
diesel-electric propulsion and have a rated capacity of 290 tonnes each.
Average fleet availability is 82%.
A breakdown of the causes of delay for the fleet is as follows:
Category Distribution of
downtime (%)
MTTR (hrs)
Motor 13.1% 8.34
Electrical 34.26% 4.79
Mechanical 28.54% 10.96
Structural 8.94% 6.56
Preventive
maintenance 6.95% 17.74
Accessories 3.41% 3.97
Miscellaneous 0.01% 0.92
Process delays 4.79% 7.94
Part A: Maintenance Performance Indices
Calculate:
(i) the total maintenance downtime (hrs) experienced by the fleet in one year (365
days). (1 mark)
(ii) total fleet up-time (hrs) in the same period (1 mark)
2
(iii) the average fleet utilisation assuming that “Process delays” incorporate
operational delays such as shift change etc. (1 mark)
(iv) the total operating hours (op hrs) of the fleet (1 mark)
(v) the expected Mean Time to Restore Service (MTTR) for the fleet (excluding
process delays). (1 mark)
(vi) the expected number of fleet maintenance interventions in one year (1 mark)
(vii) the expected number of delays/truck in each delay category (2 marks)
(viii) the Mean Time to Stoppage of the fleet (MTTS, in op hrs. This is distinct to
MTTF as not all interventions are unscheduled) (1 mark)