Question 1 of 13: Availability and Utilization

Question 1.1: Availability and Utilization (5 marks, compulsory)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Availability and utilization. An 8760-hour year (365×24) is the full CALENDAR-hour denominator against which every equipment-performance ratio in this paper is ultimately referenced. Mechanical availability is the fraction of scheduled hours a machine is mechanically capable of operating: $$MA=\dfrac{\text{scheduled hours}-\text{maintenance/repair downtime}}{\text{scheduled hours}}\times100\%$$ It answers “could the machine have run if someone wanted it to?” and excludes non-mechanical stoppages entirely. Operating (physical) availability is broader – it is the fraction of TOTAL calendar hours the machine was actually available for productive work, after subtracting mechanical downtime AND all non-mechanical delays (no operator, weather, blasting exclusion, waiting for trucks, standby): $$PA=\dfrac{8760-\text{all downtime (mechanical + non-mechanical)}}{8760}\times100\%$$ Utilization is then the fraction of the hours the machine WAS available that it actually spent producing: $$U=\dfrac{\text{operating hours}}{\text{available hours}}\times100\%$$ so overall equipment effectiveness for the year is $MA$ (or $PA$) $\times\,U$, referenced back to the full 8760-hour base.

Making the numbers look better. Because each of these ratios is a fraction, the reported percentage can be inflated either by shrinking the numerator's downtime or by shrinking the denominator's hour base, without changing anything physical about the machine. Common ways this is done: (i) reporting MECHANICAL availability alone (which counts only maintenance downtime) instead of PHYSICAL/operating availability (which also counts weather, blast delays, no-operator and standby time) – MA is always ≥ PA for the same machine, sometimes by 10–15 points; (ii) narrowing “scheduled hours” to exclude planned shutdowns from the denominator, rather than using the full 8760-hour calendar base, which removes exactly the hours most likely to contain downtime; (iii) reporting “use of availability” (utilization measured against AVAILABLE hours only) rather than against the full calendar year, which hides low availability behind a high utilization figure; and (iv) reclassifying standby/idle time as “available but not required” rather than as a utilization loss. A reader comparing fleets must always check which of these four definitions is actually being quoted before comparing numbers between mines or contractors.