Aircraft leasing terminology causes more confusion in capacity discussions than almost anything else in commercial aviation. Wet lease, damp lease, dry lease, ACMI — the terms are used loosely, sometimes interchangeably, and occasionally incorrectly, even inside airlines.
The differences matter because they determine who is responsible for what, who carries the operational risk, and what you actually pay for. Get the structure wrong and you either pay for services you do not need or discover mid-contract that a critical responsibility sits on your side of the table. Here is each structure in plain terms.
ACMI and wet lease: the operator does the flying
ACMI stands for Aircraft, Crew, Maintenance and Insurance — the four things the lessor provides. The lessee provides essentially everything else: fuel, airport and handling fees, navigation charges, catering, and crucially the commercial risk of filling the seats or the cargo capacity. The aircraft flies under the lessor's Air Operator Certificate (AOC), which means the lessor remains operationally responsible for the flight.
A wet lease is, for most practical purposes, the same arrangement; the terms are used almost interchangeably in the market. Where a distinction is drawn, ACMI usually refers to the pricing model — a rate per block hour with a minimum guaranteed monthly utilisation — while wet lease describes the arrangement generally.
Typical uses include covering seasonal peaks, replacing an aircraft stuck in maintenance, launching a route before committing your own fleet, and bridging delivery delays. Contracts commonly run from one month to two years. Our post on planning ACMI capacity covers lead times and cost drivers in detail.
Damp lease: the hybrid
A damp lease sits between wet and dry. The lessor provides the aircraft, flight crew, maintenance and insurance, but the lessee supplies its own cabin crew. Airlines choose this structure when brand consistency in the cabin matters — passengers see the lessee's uniforms and service standards — or when local labour regulations require the use of the lessee's own cabin staff.
It is a pragmatic compromise, but it needs careful handling. Cabin crew must be trained on the specific aircraft type and the lessor's safety procedures, and the split of responsibility during an operational disruption must be written down precisely, not assumed.
Dry lease: you take the keys
Under a dry lease, the lessor provides the aircraft and nothing else. The lessee places the aircraft on its own AOC, supplies its own crews, arranges its own maintenance programme and carries its own insurance. This is the domain of leasing companies and long-term fleet planning rather than short-term capacity cover; typical terms run from two years to more than a decade.
A dry lease gives full operational control and, over time, a lower cost per hour — but it also transfers all operational risk to the lessee. It only makes sense when you have the certification, the crews and the maintenance arrangements to support the type.
Who provides what: the responsibility matrix
The simplest way to keep the structures straight is to ask four questions of any proposed lease:
- Whose AOC does the aircraft fly on? Wet/damp: the lessor's. Dry: the lessee's.
- Who supplies the flight crew? Wet and damp: the lessor. Dry: the lessee.
- Who supplies the cabin crew? Wet: the lessor. Damp and dry: the lessee.
- Who pays for fuel, handling and navigation? In all structures, almost always the lessee.
If a proposal cannot answer those four questions cleanly, the contract is not ready to sign.
What ACMI actually costs, and how it is charged
ACMI pricing has a structure worth understanding before you compare quotes. The lessor charges a rate per block hour — engine start to engine stop — against a minimum guaranteed utilisation, commonly 150 to 300 block hours per month depending on aircraft type and season. Fly less than the minimum and you pay for it anyway; fly more and the additional hours are usually charged at the same or a slightly reduced rate.
On top of the ACMI rate sit the lessee's direct operating costs: fuel (the largest single item), airport and handling charges, navigation fees, catering and ground services. As a rough rule, the ACMI rate typically represents somewhere between a third and a half of the true total cost per block hour once those direct costs are added. Comparing an ACMI quote against your own fleet's costs therefore requires comparing total cost per hour, not headline rates.
Seasonality moves prices considerably. Northern-hemisphere summer is the peak for passenger ACMI demand across Europe, and rates and minimums harden accordingly; the same aircraft can be materially cheaper for a winter contract. This is the core reason early planning pays.
Common pitfalls when contracting capacity
Three mistakes recur. First, contracting on rate alone and ignoring the reliability record and spare coverage behind it — a cheap ACMI provider with no backup aircraft becomes very expensive on the first technical delay. Second, leaving the wet/damp boundary vague: if your cabin crew are operating on another carrier's AOC, the training, liability and disruption-handling arrangements must be documented before the first flight, not negotiated during a diversion. Third, ignoring traffic-rights and regulatory limits — many jurisdictions cap the share of capacity an airline may wet-lease in, and some restrict leases from foreign operators, which can constrain your options at renewal.
Choosing the right structure
The decision usually comes down to duration, control and capability. Need capacity for a season or an unexpected gap? ACMI or wet lease, because the lessor's certification and crews come with the aircraft. Want your own cabin product on someone else's metal? Damp lease. Building fleet for the long term with your own operation? Dry lease.
Cost comparisons should always be made on a total-cost basis. An ACMI block-hour rate looks expensive next to a dry lease rate until you add crewing, maintenance reserves and insurance to the dry side of the ledger.
Fliteline arranges ACMI and wet lease capacity across passenger and cargo types, with flight support available where the lessee's own network is thin. If you are weighing up structures for a coming season, talk to us early — availability, not price, is usually the binding constraint. See our ACMI leasing services for more.
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