Operations
ACMI, wet lease, damp lease and dry lease: the complete guide
In an ACMI lease, the lessor provides the Aircraft, Crew, Maintenance and Insurance and operates the flights on its own AOC, charging the lessee per block hour. "Wet lease" is the umbrella term for this arrangement; a damp lease excludes cabin crew; a dry lease provides the aircraft alone, flown on the lessee's AOC.
Few aviation terms are used as loosely as these four. What actually separates them comes down to a handful of questions, each with real consequences for the people who plan crews.
What does ACMI stand for?
ACMI spells out what the lessor brings to the deal:
- A for Aircraft: the aeroplane itself;
- C for Crew: complete crews, flight deck and cabin, trained and current;
- M for Maintenance: continuing airworthiness and upkeep;
- I for Insurance: hull and operational liability cover.
The lessee pays an agreed rate per block hour, usually against a monthly minimum guarantee, and keeps everything the acronym doesn't cover: fuel, airport and navigation charges, ground handling, crew hotels down-route, passenger taxes, plus the commercial side. Flights carry the lessee's flight numbers but are operated under the lessor's AOC.
That last point is the legal heart of the model: in ACMI, operational responsibility and safety oversight stay with the lessor, under its authority's supervision.
Wet, damp, dry: who provides what?
| Item | Wet lease (ACMI) | Damp lease | Dry lease |
|---|---|---|---|
| Aircraft | Lessor | Lessor | Lessor |
| Flight crew | Lessor | Lessor | Lessee |
| Cabin crew | Lessor | Lessee | Lessee |
| Maintenance | Lessor | Usually lessor | Lessee |
| Operational insurance | Lessor | Usually lessor | Lessee |
| AOC used | Lessor's | Lessor's | Lessee's |
| Typical horizon | Weeks to a few seasons | Weeks to a few seasons | Several years |
Four questions settle any arrangement: whose AOC? who provides the pilots? who provides the cabin crew? who pays to operate?
- Wet lease is the market's umbrella term for ACMI: aircraft plus full crew under the lessor's AOC. In practice the two words are interchangeable.
- Damp lease is the variant where the lessee supplies its own cabin crew, typically to keep its onboard product, language and service standards. Note that a damp lease has no single regulatory definition. It is industry usage, and the contract governs.
- Dry lease is the aircraft alone, registered and operated on the lessee's AOC, with the lessee providing crews, maintenance and insurance. It sits closer to fleet financing than to buying capacity.
In the EU, wet-leasing third-country-registered aircraft is constrained by Article 13(3) of Regulation (EC) No 1008/2008: equivalent safety standards must be demonstrated, and the lease justified by one of three needs — exceptional needs (up to seven months, renewable once for up to seven months), seasonal capacity needs, or operational difficulties (limited to the duration strictly necessary).
When is each model used?
- Wet lease / ACMI: seasonal peaks, aircraft delivery delays, long AOG events, trialling a new route, temporary crew shortages, rapid restarts. The lessee is buying capacity along with the scarcest resource in the market: qualified, immediately available crews. The need has become structural. At the end of 2024, IATA put the year's aircraft deliveries 30% below forecasts, with a record backlog of 17,000 aircraft and a global average fleet age pushed to a record 14.8 years (IATA press release, 10 December 2024).
- Damp lease: the same situations, when the lessee wants to keep control of the cabin experience.
- Dry lease: multi-year fleet building or renewal, when the lessee has (or is building) its own operating capability.
What ACMI means for crew planning
For an ACMI operator, the crew is the product. The margin is made or lost in the roster.
- Multiple contracts, multiple bases: the same pilots and cabin crew serve several client contracts at once, often from project bases far from home base. Each contract has its own coverage requirements, and the roster has to balance them without burning out part of the workforce.
- Compliance per contract: crews stay under the lessor's AOC and FTL scheme, but every contract layers on its own constraints (local regulations, client requirements, visas and immigration). One pilot can need to satisfy several rule sets within the same month.
- The minimum guarantee drives optimisation: guaranteed block hours only pay off if crew utilisation keeps up. An under-used crew on a project base costs twice: salary, per diem and hotels on one side, uncovered guaranteed hours on the other.
- Bid-speed matters: ACMI tenders are won in days. Being able to answer "do we have the crews for this contract?" in minutes rather than by Friday changes how an operator bids.
This is exactly the ground SkAI Tech was built for: as an add-on to the operations system already in place, it generates compliant multi-contract rosters (FTL, regional and in-house rules) in around twelve minutes, and lets planners re-run the roster whenever a contract starts or ends.
FAQ
Are ACMI and wet lease the same thing?
In practice, yes. The market uses both for the same arrangement: aircraft, full crew, maintenance and insurance provided by the lessor under its AOC. "ACMI" describes the contract's content; "wet lease" names the legal family.
Who is responsible for safety on a wet-leased flight?
The lessor: the flights are operated under its AOC and its authority's oversight. The lessee remains responsible for the commercial obligations, such as tickets, passengers and slots.
Whose flight number does an ACMI aircraft fly under?
The lessee's, since it sells the flight. The operation itself stays on the lessor's AOC. That combination is what defines a wet lease.
Is a damp lease defined in regulation?
No. Unlike the wet lease, which has a regulatory basis in Europe, a damp lease has no single regulatory definition: it is industry usage, and what it covers varies from one contract to the next. Read the contract rather than trusting the label.
Why does the damp lease exist?
To keep the lessee's product onboard: its own cabin crew, colours, language and service standards, while buying the aircraft, pilots and maintenance externally. Where exactly the line falls — cabin crew training, supervision — is set by the contract.
Sources
- Regulation (EC) No 1008/2008, Article 13(3): the conditions for wet-leasing third-country-registered aircraft (equivalent safety standards, exceptional needs, seasonal capacity needs, operational difficulties).
- Regulation (EU) No 965/2012, for the AOC and operational responsibility.
- International Air Transport Association (2024, December 10), Supply Chain Issues Continue to Negatively Impact Airline Performance into 2025: 2024 deliveries 30% below forecast, a 17,000-aircraft backlog, and a global average fleet age of 14.8 years.
- Standard ACMI contract practice, the only reference for the damp lease, which has no regulatory definition.