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Qwestrum Engineering360 · Mechanical Engineering · Maintenance Engineering

Maintenance Planning

Maintenance planning schedules tasks, crews, and spares to minimise downtime and cost; crew size = total PM hours/available hours per technician. It coordinates work orders, priorities, and spare-parts inventory, per maintenance-engineering texts.
Exam tip: keep SI units consistent end-to-end, write the governing relation symbolically before substituting, and sanity-check magnitude and sign.

Key formulas & points

Skim these first — then read the full notes below.

  • CMMS: computerised maintenance management system
  • Work order priority: safety > production > cosmetic
  • Shutdown planning: minimise production loss window

Topic details

Introduction

Maintenance planning organises the who, what, when, and with-what of maintenance work, converting strategy into executable schedules. Indian courses cover work-order systems, scheduling, and spares management.

Scope in B.Tech and GATE syllabus

Planning estimates task labour and materials, sets priorities (safety, production impact), and schedules work to minimise disruption — ideally during planned shutdowns. Crew sizing matches workload to available technician hours.

Why this topic matters in practice

Spare-parts inventory (using EOQ and criticality analysis) ensures parts are available without excessive stock. A computerised maintenance management system (CMMS) supports this. Computing crew size and planning schedules are the exam tasks.

Key relations & formulas

Formulas (Indian textbook notation)

  • Crew sizing = total_{PM}_\frac{hours}{available_{hours}}_per_{technician}

Formulas (Indian textbook notation)

  • Backlog = open_{WO}_count \times average_{completion}_time

Formulas (Indian textbook notation)

  • PMcompliance=completedPMscheduledPM×100PM compliance = \frac{completed_{PM}}{scheduled_{PM}} \times 100%

Formulas (Indian textbook notation)

  • Spareparts:reorderpoint=d⋅L+safetystockSpare parts: reorder point = d\cdot L + safety_{stock}

Notation and sign conventions

Relation 1 —
Crew sizing = total_{PM}_\frac{hours}{available_{hours}}_per_{technician}

Formulas (Indian textbook notation)

  • Crew sizing = total_{PM}_\frac{hours}{available_{hours}}_per_{technician}
Write this relation with symbols exactly as in Maintenance Engineering — SRK Rao before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 2 —
Backlog = open_{WO}_count \times average_{completion}_time

Formulas (Indian textbook notation)

  • Backlog = open_{WO}_count \times average_{completion}_time
Write this relation with symbols exactly as in Maintenance Engineering — SRK Rao before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 3 —
PMcompliance=completedPMscheduledPM×100PM compliance = \frac{completed_{PM}}{scheduled_{PM}} \times 100%

Formulas (Indian textbook notation)

  • PMcompliance=completedPMscheduledPM×100PM compliance = \frac{completed_{PM}}{scheduled_{PM}} \times 100%
Write this relation with symbols exactly as in Maintenance Engineering — SRK Rao before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 4 —
Spareparts:reorderpoint=d⋅L+safetystockSpare parts: reorder point = d\cdot L + safety_{stock}

Formulas (Indian textbook notation)

  • Spareparts:reorderpoint=d⋅L+safetystockSpare parts: reorder point = d\cdot L + safety_{stock}
Write this relation with symbols exactly as in Maintenance Engineering — SRK Rao before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Fundamentals and definitions

Planning defines each job's scope, labour, tools, parts, and duration before scheduling fixes when it happens. Good planning maximises wrench time (productive work) and minimises delays waiting for parts or access.

Governing relations in practice

Crew sizing balances workload and capacity: crew size = total maintenance hours required/available hours per technician; over-sizing wastes labour, under-sizing causes backlogs and deferred work.

Design and analysis considerations

Work is prioritised by criticality — safety and production-critical equipment first — and scheduled to coincide with production breaks or planned shutdowns to avoid unplanned downtime. Backlog management prevents work from accumulating.

Advanced theory and extensions

Spare-parts planning uses criticality (VED analysis) and inventory models (EOQ, safety stock) to stock the right parts: critical/long-lead items are held despite low usage, while common items follow economic ordering. A CMMS integrates work orders, schedules, history, and inventory. Balancing crew, schedule, and spares to minimise total downtime cost is the planning objective.

Assumptions and validity limits

State assumptions explicitly before using any relation for maintenance planning — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.
Wrong assumptions invalidate the entire solution even when the formula is correct. In Maintenance Engineering viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

Step-by-step problem approach

1. Read the question and list given data with SI units (common in Maintenance Engineering papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to maintenance planning.
4. Use equation 1:
Crew sizing = total_{PM}_\frac{hours}{available_{hours}}_per_{technician}
.
5. Use equation 2:
Backlog = open_{WO}_count \times average_{completion}_time
.
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

Applications & exam relevance

Maintenance Planning appears in process plants and utilities. In Indian mechanical curricula this topic is tested because it connects theory to reliability and upkeep of plant equipment.
GATE and semester exams often combine maintenance planning with earlier units — revise prerequisites before attempting mixed problems.
Industry interview panels sometimes ask: "Where did you use maintenance planning?" — answer with a lab, mini-project, or plant visit example if possible.

Common mistakes in exams

• Confusing planning (scope/resources) with scheduling (timing)
• Ignoring equipment criticality when prioritising work
• Sizing crews from calendar time rather than available productive hours
• Under-stocking critical long-lead spares to save inventory cost

Quick revision checklist

Before attempting maintenance planning problems, confirm you can:
1. CMMS: computerised maintenance management system
2. Work order priority: safety > production > cosmetic
3. Shutdown planning: minimise production loss window
Revise the solved examples in Maintenance Engineering — SRK Rao and one previous-year GATE or university paper for this unit.

Worked examples

Try the problem first — open the solution when you are ready to check.

Maintenance crew size

Problem

Monthly PM workload is 640 technician-hours; each technician provides 160 productive hours per month. Find the required crew size.

Solution

Crew size = total PM hours/available hours = 640/160 = 4 technicians.

Conceptual check — Maintenance Planning

Problem

In a Maintenance Engineering semester or GATE paper you are asked: "State the main assumption, the governing relation, and one practical consequence of maintenance planning." What should a complete answer include?

Practice questions

Most-asked interview and GATE questions for this topic — expand any item for a model answer.

  1. 1
    What is Maintenance Planning, and why does it appear in B.Tech / GATE syllabi?

    Model answer

    Maintenance planning schedules tasks, crews, and spares to minimise downtime and cost; crew size = total PM hours/available hours per technician. It coordinates work orders, priorities, and spare-parts inventory, per maintenance-engineering texts.
  2. 2
    State the relation Crew sizing = total_PM_hours/available_hours_per_technician and name each symbol.

    Model answer

    The governing relation is Crew sizing = total_{PM}_\frac{hours}{available_{hours}}_per_{technician}. Write every symbol with SI units before substituting numbers.
  3. 3
    State the relation Backlog = open_WO_count × average_completion_time and name each symbol.

    Model answer

    The governing relation is Backlog = open_{WO}_count \times average_{completion}_time. Write every symbol with SI units before substituting numbers.
  4. 4
    State the relation PM compliance = completed_PM/scheduled_PM × 100% and name each symbol.

    Model answer

    The governing relation is PMcompliance=completedPMscheduledPM×100PM compliance = \frac{completed_{PM}}{scheduled_{PM}} \times 100%. Write every symbol with SI units before substituting numbers.
  5. 5
    State the relation Spare parts: reorder point = d·L + safety_stock and name each symbol.

    Model answer

    The governing relation is Spareparts:reorderpoint=d⋅L+safetystockSpare parts: reorder point = d\cdot L + safety_{stock}. Write every symbol with SI units before substituting numbers.
  6. 6
    Explain: CMMS: computerised maintenance management system

    Model answer

    CMMS: computerised maintenance management system — state the assumption range and one exam trap linked to this point.
  7. 7
    Explain: Work order priority: safety > production > cosmetic

    Model answer

    Work order priority: safety > production > cosmetic — state the assumption range and one exam trap linked to this point.
  8. 8
    Explain: Shutdown planning: minimise production loss window

    Model answer

    Shutdown planning: minimise production loss window — state the assumption range and one exam trap linked to this point.
  9. 9
    How would you correct this error in a viva: Confusing planning (scope/resources) with scheduling (timing)?

    Model answer

    Identify the wrong assumption or unit mix-up, rewrite the correct relation, and recompute with a one-line sanity check.
  10. 10
    How would you correct this error in a viva: Ignoring equipment criticality when prioritising work?

    Model answer

    Identify the wrong assumption or unit mix-up, rewrite the correct relation, and recompute with a one-line sanity check.
  11. 11
    How would you correct this error in a viva: Sizing crews from calendar time rather than available productive hours?

    Model answer

    Identify the wrong assumption or unit mix-up, rewrite the correct relation, and recompute with a one-line sanity check.
  12. 12
    How would you correct this error in a viva: Under-stocking critical long-lead spares to save inventory cost?

    Model answer

    Identify the wrong assumption or unit mix-up, rewrite the correct relation, and recompute with a one-line sanity check.

Exams & GATE

  • 1
    SRK — criticality matrix (probability × consequence) ranks assets.
  • 2
    Avoid: Confusing planning (scope/resources) with scheduling (timing)
  • 3
    Avoid: Ignoring equipment criticality when prioritising work
  • 4
    Avoid: Sizing crews from calendar time rather than available productive hours

📖 Standard books (India)

  • Maintenance Engineering — SRK Rao

    Read: Syllabus unit

    Reliability, RCM, and maintenance planning

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