The 600-hour check: turning flight-hour forecasts into a staffing plan
A 600 FH / 24M check is the bread-and-butter input of most helicopter Part-145 shops — and yet most of them are planned backwards. The planner books a hangar slot, then discovers the crew numbers. Do it the other way round: forecast the trigger date, convert it to man-hours, then check whether your roster can actually deliver them. Here is the five-step method, with real numbers.
01Step 1 — Forecast the trigger date, honestly
Start from actual utilisation, not last year's assumption. Take the last three months of flight hours per tail and average them. If your AW139 flew 38, 47 and 50 hours, plan on 45 FH/month — not on the 35 the CAMO agreement says.
example: (600 − 380) ÷ 45 ≈ 4.9 months → input due mid-March
Then bracket it: at ±20% utilisation swing, that same check lands anywhere from early February to late April. Your staffing plan must survive the earliest date, because that is the one the customer will hold you to.
02Step 2 — Convert the package to man-hours
A scheduled AW139 600 FH/24M package runs roughly 1,400 man-hours from the task cards alone. Nobody has ever delivered one at card value. Add the findings factor your own history gives you — across the fleets I instruct on, routine rectification grows a 600h check by 25–35%:
1,400 × 1.30 ≈ 1,820 man-hours
03Step 3 — Split the hours by license category
Total hours are meaningless for staffing until you split them by who can certify them. A typical 600h/24M split on an AW139:
| Category | Share of hours | Man-hours (of 1,820) | Certifying hours |
|---|---|---|---|
| B1 mechanical (airframe/engines) | 55% | 1,001 | ~130 |
| B2 avionics | 30% | 546 | ~85 |
| C / base-check certification | — | — | ~30 |
| Support (sheet metal, NDT, shop visits) | 15% | 273 | — |
| Total package | 100% | 1,820 | ~245 |
The column that sinks schedules is the last one: 245 hours of work only a type-rated certifying engineer can touch. That is the binding constraint, not headcount.
04Step 4 — Run the crew arithmetic
Nobody produces eight productive hours in an eight-hour shift. Briefings, tool control, parts runs and paperwork leave 6.0–6.5 productive hours per engineer per day. For a 12-working-day input:
1,820 ÷ (12 × 6.2) ≈ 24.5 productive-days per day → ~7–8 engineers on the aircraft
Now check the roster: of those 8, you need at least 2 B1 and 1 B2 certifying staff available every single day — including the days where leave, training or a line AOG pulls one away. If your plan only works at 100% attendance, it doesn't work.
05Step 5 — Re-run it every quarter
Utilisation drifts, findings factors drift, rosters drift. AMC1 145.A.30(d) expects the man-hour plan to be reviewed against actuals on a rolling basis — so re-run steps 1–4 each quarter, and treat a trigger date that moved more than a month as a replanning event, not a footnote. The check you forecast in January will not be the check that arrives in March unless the numbers say so.
Skip the spreadsheet: enter your fleet's utilisation and the calculator forecasts trigger dates, converts check packages to man-hours, and stress-tests your B1/B2 coverage — with an auditor-ready PDF.
Plan your next 600h check →