Wet lease explained: why other airlines’ aircraft fly for your airline

You’re standing on the deck, a SWISS flight is running on your tracking app’s display – and then an Airbus A220 with a Latvian registration and a lime-green vertical stabilizer touches down. Not a bug in the app, but a wet lease: one airline flies with aircraft and crew on behalf of another. For passengers it is sometimes a surprise at the gate, for spotters often the best moment of the day. Here you learn what is behind the model, which rules apply in the EU, why airlines resort to it and how you can reliably recognize such operations.

Wet lease: the short answer

A wet lease is a rental contract between two airlines in which the lessor provides not only the aircraft but also the crew, maintenance and insurance. The renting airline sells the tickets, assigns its flight number and pays for fuel and airport fees. The aircraft, however, continues to be operated by the lessor – under its operator certificate, with its pilots and according to its manuals.

The “wet” in the name symbolizes that everything an aircraft needs to fly comes with it – as opposed to the “dry” lease, in which only the bare machine changes hands. In the industry the abbreviation ACMI is also common for a wet lease: Aircraft, Crew, Maintenance, Insurance.

Who provides what? The division of tasks in detail

The decisive question in a wet lease is who bears operational responsibility. EU aviation law answers it clearly: in the definitions of Regulation (EU) No 965/2012 on air operations, a wet lease in commercial air transport is a contract between air carriers in which the aircraft is operated under the lessor’s air operator certificate (AOC). With a dry lease it is the other way around: the aircraft flies under the lessee’s AOC.

In practice the tasks are usually divided like this:

Area	Lessor	Lessee
Aircraft	provides it, including registration	–
Flight deck and cabin crew	provides them (only the flight deck in a damp lease)	possibly own cabin crew in a damp lease
Maintenance and airworthiness	responsible	–
Insurance	responsible	–
Fuel	–	generally pays for it
Airport and air traffic control fees	–	generally bears them
Ticket sales, flight number, ground handling	–	organizes them

With ACMI contracts, billing is typically based on hours flown. The lessee gets capacity without having to buy aircraft, hire crews or build maintenance structures for another type. The lessor, in turn, can keep its fleet busy even when it doesn’t have enough demand on its own routes.

Wet, damp, dry: three terms, three models

For you as a spotter the difference matters: a dry-leased aircraft usually can’t be told apart from the outside from a purchased one. It wears the colors and, as a rule, the national registration of the airline that flies it. A wet-leased aircraft, on the other hand, stays in the lessor’s fleet – with its registration and often its livery.

Why airlines charter other airlines’ aircraft

Hardly any airline has exactly as many aircraft as it needs all year round. Wet leases are the tool for closing gaps at short notice without permanently enlarging your own fleet. The most common occasions:

• Seasonal peaks: In summer, vacation routes carry significantly more passengers than in winter. Instead of keeping extra aircraft all year, airlines rent capacity for a few months.
• Delivery delays: If new aircraft arrive from the manufacturer later than agreed, seats are missing in the schedule. A wet lease bridges the time until the airline’s own aircraft arrive.
• Shop and engine problems: Major maintenance events or engine inspections ground aircraft for weeks or months. Rented capacity keeps the schedule stable.
• Short-notice outages: If an aircraft goes out of service technically, an ACMI aircraft sometimes steps in for a few days or even just one rotation.
• Testing new routes: An airline can try out a connection with borrowed capacity before tying up its own aircraft for it.
• Cost structure: Smaller aircraft of a specialized operator can be cheaper on thin routes than the airline’s own type.

What EU law allows

In the EU, Article 13 of Regulation (EC) No 1008/2008 on the operation of air services governs leasing. The basics in our own words:

• EU airlines may use aircraft under dry or wet leases.
• Wet-leased aircraft that are registered in the EU they may generally use freely, as long as safety is not endangered.
• For a wet lease in which the EU airline is the lessee, prior approval under the applicable safety rules is required.
• For aircraft registered outside the EU, things get much stricter: the airline must prove equivalent safety standards to the approving authority and cite one of three reasons.

Reason for a third-country wet lease	Condition	Duration of approval
Exceptional need	special circumstances	up to seven months, extendable once by up to seven months
Seasonal capacity need	cannot reasonably be met with EU-registered aircraft	extendable
Operational difficulties	no suitable EU aircraft reasonably available	only as long as strictly necessary

Since an amendment by Regulation (EU) 2019/2, international agreements of the EU with individual third countries can deviate from these conditions – one example is the air transport agreement between the EU and the USA, which provides for more open rules on wet leases. In addition, the authority can refuse an approval if the state of registration, conversely, does not allow wet leases from EU airlines.

Behind this is a balancing of interests: airlines want to stay flexible, while the legislator wants to prevent safety standards and working conditions in Europe from being undermined by cheap crews from third countries. That is why third-country wet leases are rather the exception in Europe, while intra-EU ACMI contracts are an everyday matter.

Wet leases you see in Central Europe

At airports in Germany, Austria and Switzerland in particular, ACMI aircraft are part of everyday life. Two examples you are very likely to catch yourself:

airBaltic for the Lufthansa Group: Latvia’s airBaltic flies exclusively the Airbus A220-300 and leases part of its fleet with crew to other airlines. Since 2022 it has flown for SWISS, among others, and in 2023 approval for long-term wet leasing within the Lufthansa Group was added. In early 2025, according to reports, a large part of the airBaltic fleet – nearly half – was deployed for the group. At the fence you recognize the aircraft by the registration with the Latvian prefix YL- and by the airBaltic livery – even if the flight carries an LX or LH number.

Helvetic Airways for SWISS: Helvetic Airways from Zurich has been flying wet lease for SWISS for years. In 2018 the two airlines agreed an expansion of their cooperation, and from 2019 up to eight aircraft were planned. During the pandemic the number was reduced. Embraer jets such as the E190 and the E190-E2 are typically in service. Since Helvetic is also registered in Switzerland, the jets carry an HB- registration like the SWISS fleet – here only a look at the livery, type and operator information in the tracking app helps you. From spectator deck B or the Butzenbüel at Zurich Airport you often see both models in direct alternation.

There are also pure ACMI specialists that operate practically no network of their own. A well-known example is Portugal’s Hi Fly, which leases aircraft with crew to airlines, tour operators and governments and even took over a used Airbus A380 in 2018. When such an exotic shows up unannounced at your airport, there is almost always a short-term capacity bottleneck at an airline behind it.

How to recognize a wet lease at the fence

A wet lease almost always gives itself away through a contradiction: flight number, registration and livery don’t fit together. Four checks will get you to the bottom of any case.

Steps 3 and 4 in particular work best with live data. How to identify aircraft in the air via ADS-B is covered in the guide Flight tracking with ADS-B for spotters, and the flight tracker app comparison gives an overview of the common apps. And how registrations are structured in general is in Understanding aircraft registrations.

Typical patterns at a glance

What you see	What it usually means	Wet lease?
Foreign country prefix, foreign livery, airline’s flight number	Classic ACMI with lessor crew	very likely
Own colors, own country prefix, airline’s flight number	Own or dry-leased aircraft	no
Same country prefix, different livery, airline’s flight number	Wet lease from an airline in the same country or group	quite possible
Neutral white aircraft with small titles	ACMI specialist or freshly taken-over aircraft	check
Airline colors, but foreign registration	Dry lease with foreign registration or group aircraft	check

Why wet leases are so exciting for spotters

Wet leases bring variety to everyday life at your home airport. Suddenly types land that your regular airlines don’t even have in their fleet, registrations from countries that otherwise hardly visit, and liveries you only know from photo databases. For everyone who collects registrations, that is a real bonus – many of these aircraft show up for only one season and are gone again afterward.

A few tips so you don’t miss the opportunities:

• Keep an eye on the start of the season: Many ACMI contracts start with the summer schedule at the end of March and end with the winter schedule at the end of October. The first and last weeks are the most exciting time.
• Watch for delivery delays: When an airline publicly reports late deliveries, the chance of replacement capacity is especially high.
• Take short-notice operations seriously: If an ACMI aircraft steps in for only one day, it is often just a single rotation. Then every minute counts.
• Take notes: If you record date, flight number and registration, you will recognize your airport’s patterns over time. How to organize this cleanly is in the article Logging sightings: the spotter’s logbook.

You’ll find more ideas for unusual subjects in the guide Spotting rare aircraft. And if you’re interested in why partner aircraft show up so often within alliances, the overview of Star Alliance, oneworld and SkyTeam is worth a look – codeshares, by the way, are something different from wet leases: there, one airline sells seats on a flight that another airline operates entirely on its own.

Typical pitfalls

• A wet lease is not a codeshare. With a codeshare, only a partner airline’s flight number appears on a regular flight. With a wet lease, an airline buys capacity and sells the flight as its own.
• Not every foreign registration is a wet lease. Group airlines swap aircraft among themselves, and some airlines operate foreign-registered aircraft on dry lease under their own AOC.
• The app isn’t always right. Tracking services sometimes automatically assign flights to the airline of the flight number. When in doubt, the registration on the aircraft counts.
• The cabin product can differ. If you fly yourself: seat pitch, onboard service and entertainment often follow the lessor.

Conclusion

At its core, a wet lease is a capacity deal: an airline rents a complete aircraft including crew, maintenance and insurance and sells the flights under its own flight number, while the lessor is responsible for operations under its own operator certificate. In the EU, such contracts with EU-registered aircraft are an everyday matter, whereas aircraft from third countries need a good reason and an approval. For you as a spotter that means: if you read registration, livery and flight number together, you discover aircraft at your own airport that actually don’t belong there.