Operations
Block hours and crew utilisation in ACMI: making the guarantee pay
In ACMI, the block hour is the billing unit: the contract usually guarantees a monthly minimum the lessee pays whether it flies it or not. For the lessor, margin therefore depends less on the volume sold than on the ability to cover it with a crew complement sized exactly right.
The instinctive approach is to size against the aircraft: how many hours can this airframe fly? In practice it is almost always the crew that caps output, and how they are rostered decides whether the contract makes money.
What is the minimum guarantee and why does it structure everything?
An ACMI contract typically defines a monthly volume of block hours billed regardless, with a rate per additional hour beyond it. Terms vary from one contract to the next, but that structure has three direct planning consequences:
- Revenue is predictable, cost is not. Salaries, allowances and positioning run whether the aircraft flies or not. Any guaranteed hour left unflown for want of crew destroys margin twice: the cost is committed, the capacity is gone.
- Exceeding the guarantee is not automatically good news. Flying beyond the guaranteed volume only pays if the marginal crew cost stays controlled; otherwise overtime, reinforcement and extensions eat the upside.
- Coverage beats fine-grained optimisation. A brilliant roster that leaves a coverage gap on a project base costs more than an average roster that holds.
As a reminder from our guide to ACMI, wet, dry and damp lease: in ACMI the lessor provides aircraft, crew, maintenance and insurance, while fuel, charges, ground handling and hotels for rotating crews usually stay with the lessee. Of the costs the lessor manages day to day, crew is the one whose utilisation swings most from one roster to another.
Why is crew the real limiting factor?
An aircraft can fly far more hours than a crew complement permits. Between flight and duty limits, mandatory rest, leave, training and rotation cycles between bases, annual capacity per crew member is considerably lower than a quick reading suggests.
Three recurring gaps between theoretical and real capacity:
- Rotation time between bases. Deadheading days and the rest attached to a project-base cycle do not show up as flying, but they consume capacity.
- Structural unavailability. Leave, recurrent training, medicals, qualification expiry: this baseline is either planned, or endured mid-season.
- Rolling counters. A crew member can be present and legally unavailable because they are approaching a 28-day ceiling, or the 900 hours of the calendar year (see our ORO.FTL guide). It is the least visible gap in any manual tracking.
How do you improve utilisation without degrading conditions?
- Measure real utilisation, not headcount: block hours per available crew member, share of time consumed by positioning, coverage rate of the minimum guarantee per contract.
- Cut positioning by synchronising rotation cycles better. It is usually the first pocket of value, and one that costs crews nothing.
- Smooth plannable unavailability (leave, recurrent training) away from coverage peaks by planning it with production rather than after it.
- Use legal margin without living on it: extensions and reserve exist to absorb variability, not to compensate structural understaffing. A roster that relies on them routinely will produce deviations and attrition.
- Track planned versus actual: it is the indicator that exposes tight sizing before clients notice it.
These trade-offs get harder as soon as several contracts share the same crew pool: that is the subject of our article on rostering crews across multiple ACMI contracts.
An optimisation engine handles these trade-offs simultaneously (guarantee coverage, positioning cost, crew fairness, compliance), where manual work must pick one criterion at a time. That is what SkAI Tech adds as an add-on to the existing operations system, with multi-contract rosters generated in around twelve minutes.
Accountable for contract margins? See what SkAI Tech changes for operations leaders.
FAQ
How do I know whether my crew complement is right-sized?
Work from contractual coverage rather than aircraft count: guaranteed hours per contract, converted into available crews per base, uplifted for structural unavailability and a variability margin. If the plan only holds by using extensions systematically, the complement is too tight.
Is it better to decline a contract than to under-cover it?
Economically, often yes: a coverage failure costs penalties and commercial reputation well beyond the contract's margin. Hence the value of being able to simulate crew feasibility before answering a tender.
Do positioning hours count towards billed block hours?
That depends on the contract, and it is worth settling explicitly in negotiation. For planning purposes, what matters is that they consume duty time and capacity whether they are billed or not.
Sources
- Regulation (EC) No 1008/2008, Article 13: leasing of aircraft with crew (wet lease).
- EASA, Easy Access Rules for Air Operations, ORO.FTL.210: cumulative flight time and duty limits.
- ACMI market contract practice (minimum guarantee, additional hours): common structures, which vary from one contract to the next.
- SkAI Tech indicators (first-party data): average generation time observed across 2025-2026 deployments, varying with fleet size and operating model.
