How to calculate MRO man-hours per AMC1 145.A.30(d)

Every EASA Part-145 maintenance organisation must produce a man-hour plan showing that it has enough staff for the work it commits to — and keep that plan honest as reality diverges from it. Yet ask ten maintenance managers how their number was calculated and nine will point at a spreadsheet built by a predecessor. This guide lays out the complete, defensible method: the same one implemented in our free man-hour calculator.

01Workload: what the fleet demands

Start from physics, not headcount. Each aircraft generates scheduled and unscheduled (line + defect) workload:

• Scheduled checks. Every check type has an interval (flight hours or calendar) and an expected man-hour content. Annual scheduled man-hours per aircraft = Σ (annual flight hours ÷ interval) × check man-hours.
• Line maintenance. Daily/weekly checks, transit and turnarounds scale with utilisation — a per-flight-hour coefficient per type.
• Defect / non-routine allowance. Rectification, AOG response and deferred defects. Industry planning practice adds 10–20% on top of routine workload.

Type coefficients differ significantly — a 600 FH/interval, 250 MH check on an AW139 is not interchangeable with an H135 (≈120 MH) or an S-92A (750 FH interval, ≈450 MH). Use published maintenance-planning data for your types, then calibrate against your own records — surveyors explicitly accept calibrated in-house figures.

02Coverage: what the roster demands

Workload tells you how many productive hours you need. Coverage tells you how many people you need regardless of workload — the minimum presence to hold an AOC/approval:

• Minimum manning per shift — rarely below 2 for anything beyond day-only line work (single-person shifts are a classic Human Factors finding).
• Shift pattern multiplier — day-only (1 shift), extended (2 shifts), 24/7 (typically 2×12h, needing ~2 shift teams' worth of coverage per position).
• Rotation factor — offshore and detached operations multiply coverage demand: a 6-weeks-on/6-weeks-off pattern needs 2.0× the people per position; 6-on/3-off ≈ 1.5×; permanent local staff ≈ 1.25× (leave, training, sickness).

03The establishment: take the maximum, then add group functions

Per base, the true requirement is the higher of workload-driven and coverage-driven demand. Under-coverage shows up as audit findings; under-workload shows up as the 25% deviation. Then add the functions that don't turn wrenches:

• Supervision / shift leads — typically 10–15% of performing staff.
• Maintenance planning — one planner per ~8 engineers is a defensible planning norm.
• Compliance monitoring — minimum 0.5 FTE at group level; may be contracted.
• Certifying staff ratio — of the performing establishment, typically ~40% holding company authorisation, with at least one per base per shift pattern.

04Worked example — 5 × AW139, single base

Note how the answer is coverage-driven, not workload-driven — a result that surprises managers who size teams from check hangar loads alone. This is exactly the number an auditor probes: "why 11?" With this derivation, the answer is one page long.

05Operate the plan: monthly deviation, quarterly review

• Monthly: compare available man-hours (rostered − leave − training − sickness) against plan/12. Over 25% shortfall = significant deviation — report it, don't hide it. A self-reported deviation with a recovery plan is a non-finding; a discovered one is not.
• Quarterly: review the plan against actuals, record the review date, and keep the history. The review records are what the surveyor asks for first.
• On change: new aircraft type, new base, new rotation contract → re-run the plan before committing.