Wet leasing – also known as ACMI - is a term peculiar to the aviation industry and refers to the leasing of an aircraft to an airline, along with a crew to fly the plane and provide the onboard service.

So, if wet leasing an aircraft includes flying and cabin crew, what are dry leasing and damp leasing? Dry leasing in aviation terms is the straightforward leasing of an aircraft alone. Damp leasing is when the airline chooses to use its own cabin crew.

A comparison might be for renting office space; you could rent just the building or a floor in a building, in which case you’d have to pay for fitting the space out yourself, or you could use a serviced office facility which might be a bit more expensive but comes with some staff and office suites. The serviced office space, like wet leased aircraft, can be put in place fast, is less hassle and comes with coffee provided. It’s aircraft leasing that comes with a drink!

Getting technical with ACMI

The technical term for wet leasing is ACMI which stands for:

Aircraft
Crew 
Maintenance 
Insurance

These are the aspects of the operation that the wet lease airline takes care of, while the airline client will still be responsible for paying for direct operating costs such as catering and fuel, as well as costs such as airport fees, ground handling charges and navigation fees
While this illustration clearly applies to passenger air services, wet leasing of aircraft is not just the preserve of passenger airlines but is also widely used for air freight.

Why will an airline choose to wet lease aircraft?

There are numerous reasons for an airline to decide it needs a wet leased aircraft. Some can be planned but many are in response to events outside its control. Read on to find out why and how airlines use wet leasing to:

• Deal with unexpected delays or maintenance.
• Mitigate the effects of a delay in new aircraft deliveries.
• Increase capacity around times of peak demand.
• Experiment with new routes.

Airlines often turn to wet leasing when they want to ensure smooth operations during peak times, to deal with unexpected delays or maintenance, or as a means of testing new routes. Wet lease aircraft also serve as a means of reducing service disruption in the event of unforeseen situations such as a lack of available crew or technical faults. ACMI leasing allows airline operators to continue a seamless service without affecting their service.

The most pressing need will be when an aircraft develops a technical problem and can’t be flown. To minimise service disruption, a wet lease aircraft can be slotted into the schedule to operate the flights that should be flown by the faulty aircraft.

Some of the most dramatic instances of this happening have been when a problem has developed with an aircraft type and the model has been grounded. This happened with the B787 Dreamliner in 2013 following several electrical fires stemming from issues with its lithium-ion batteries. It also happened with the 737 MAX aircraft in March 2019 after problems were identified with the manoeuvring system, and then again after engine issues were identified with some B787 aircraft. In 2024, some airlines are once more rushing to lease planes after the grounding of the Boeing 737 Max.

Another occasion when there is a need to bring in a wet leased aircraft at short notice is when scheduled maintenance on an aircraft takes longer than planned and the plane can’t be returned to the fleet when expected.

Airlines usually have more notice of when deliveries for new aircraft they have ordered are running late. While fleet planning teams may have planned schedules on the assumption that new aircraft will be arriving by a certain point in time, wet leased aircraft can fill the gap when there are delays.

When the market for aircraft is constrained and demand for air travel outpaces supply, airlines can find themselves short of capacity, especially in peak periods. By making use of wet leasing, airlines are able to increase capacity and generate revenues and cash while demand for travel is high. ACMI leasing provides a flexible solution to immediate and strategic capacity demands. Similarly, wet leased aircraft allow airlines to experiment with opening up new routes which they believe to be commercially viable without the long-term commitment of adding to the fleet.

As with peak seasonality, airlines sometimes find opportunities where demand is for a short period only, such as major sporting events. Using wet leased aircraft on these occasions allows the airline to market and promote its own airline without the long-term commitment to taking on additional aircraft.

Finally, wet leased aircraft can be useful for the new airline start-up which is looking for rapid market entry but maybe doesn’t have the funds in place to purchase dry lease an aircraft.

As all these examples show, the use of wet lease aircraft is usually for a fairly short period of time, contrasting with the typical dry lease contract which lasts for years. The wet lease model allows airlines to scale up capacity at short notice without capital expenditure as the wet lease aircraft are charged by the block hour.

Who are the players?

The global Aircraft ACMI Leasing market size is projected to reach USD 7667.1 million by 2028, from USD 4779.8 million in 2021, at a CAGR of 6.9% during 2022-2028.

ACMI leasing has been more established in North America, particularly in the US and, as contracts have become longer, the model has morphed into one of Capacity Purchase Agreements (CPA) such as those operated by Mesa Air which operates regional jet flights on behalf United Airlines. In the cargo sphere, online shopping company Amazon has long term contracts with ACMI leasing operators to handle its freighter operations.

The European wet leasing market had been growing strongly prior to the pandemic, and last year saw a significant increase in demand as airlines started to feel the effect of aircraft production delays.

Some of the better known ACMI operators include Air Belgium, CityJet, Euro Atlantic Airways, GetJet Airlines, Hi Fly, SmartLynx, Titan Airways and Wamos Air.

Can we tell if a flight is wet-leased?

The short answer, at least for the air traveller, will be yes as the branding and livery of the aircraft will be different, maybe even the aircraft model used will be different to the type that was booked. These are things that passengers could notice, but for the airline the flight operation may appear just as any other flight in the schedule. It will carry the same airline code and may be operating to a schedule that the airline has flown for years. This seamless integration is one of the attractions.

How Did The pandemic Impact The ACMI Industry?

With wet lease aircraft generally providing additional capacity as needed, the immediate effect of the pandemic was to severely impact the wet lease market. Airlines parked numerous aircraft in storage or kept them under-utilised, while ACMI operators had a surplus of capacity. While demand was weak, airlines operated smaller aircraft. Qantas, for example, wet leased three E-190’s in order to operate some domestic routes which would previously have been operated with much larger 737-800’s. This is a typical example of the way that wet lease aircraft can provide airlines network flexibility as and when they require it.

As demand recovers, and problems with aircraft supply continue, wet leasing continues to provide a flexible and speedy way to bring capacity back, capture market share and take advantage of route opportunities as they emerge. However, the low rates we saw while wet lease operators had that surplus supply are now a distant memory.

*Updated: 23.06.2021*

*Updated: 30.1.2024*

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