When an airline needs capacity quickly, buying or dry-leasing an aircraft may not solve the immediate problem. The airline would still need to place the aircraft on its air operator certificate, train crews, arrange maintenance and create an operational support system. A wet lease provides the aircraft together with the organisation required to operate it. In commercial language, many agreements are described as ACMI: aircraft, crew, maintenance and insurance.
Under a wet lease for commercial air transport, the aircraft is normally operated under the air operator certificate of the lessor. The lessor supplies the flight crew, usually the cabin crew, the maintenance programme and defined insurance. The lessee sells the seats or cargo capacity and integrates the service into its network. The exact division of cost and responsibility is written into the contract and must comply with the regulators overseeing both operators.
Wet lease, dry lease and damp lease
A dry lease provides the aircraft without crew. The lessee operates it under its own air operator certificate and assumes operational control, crew, maintenance and continuing-airworthiness responsibilities according to the approved arrangement. A dry lease can support long-term fleet growth but requires time and regulatory work.
A wet lease provides aircraft and crew under the lessor’s operational responsibility. In European rules, a wet-lease aircraft used for commercial air transport is operated under the lessor’s AOC. The lessee cannot treat the flight as if it were simply using its own spare aeroplane.
A damp lease is an industry term for an arrangement in which the lessor provides the aircraft and flight crew while the lessee provides some or all cabin crew. The regulatory treatment depends on jurisdiction and contract. Cabin crew from two organisations may need aircraft-specific and operator-specific training before working together.
CMI arrangements may provide crew, maintenance and insurance for an aircraft owned or supplied separately. Terminology varies, so the legal responsibilities matter more than the label.
What ACMI normally includes
The aircraft component covers an airworthy aeroplane in an agreed configuration. The contract identifies registration, type, seating, cargo capability, navigation approvals and equipment. Substitution rights may allow the lessor to provide another aircraft if the nominated one becomes unavailable.
Crew includes qualified pilots and, in a full wet lease, cabin crew. The lessor manages licences, recurrent training, flight-time limitations, medical status and rostering. The crews operate according to the lessor’s manuals and procedures, not the lessee’s normal cockpit methods.
Maintenance covers line and base maintenance, defect control, required spares and continuing-airworthiness management within the agreed scope. Insurance covers defined hull and liability risks. Policies, limits and named insured parties are checked before operation.
What the lessee usually supplies
The lessee commonly pays for fuel, airport charges, ground handling, catering, passenger services, navigation charges and route-specific costs. It normally holds the commercial relationship with the passenger and controls schedule, pricing and distribution.
Traffic rights, airport slots and route authorities may remain the lessee’s responsibility, but the operating carrier must be authorised to fly the route. A slot held by one airline cannot automatically be used by any aircraft without coordination.
Contracts allocate extraordinary costs such as de-icing, diversions, crew hotels, maintenance away from base and passenger compensation. A vague agreement can turn a technical disruption into a legal dispute.
Operational control remains with the lessor
Operational control means authority over the initiation, continuation, diversion and termination of a flight. Under a wet lease, the lessor’s authorised personnel and commander retain safety decisions.
The lessee may request a schedule and destination, but it cannot direct the crew to depart contrary to the lessor’s manuals, weather minima or duty limitations. The lessor’s operations control centre releases or supports the flight.
Coordination is essential because the lessee manages passengers and network consequences while the lessor manages the aircraft operation. Both need accurate information during delays and diversions.
Regulatory approval
Wet leases are subject to regulatory oversight. EASA rules require approval for relevant lease-in arrangements and define additional conditions for aircraft from third-country operators. Authorities examine the lessor’s AOC, continuing-airworthiness standards, certificate of airworthiness, operating areas and safety oversight.
A third-country operator serving Europe may need an EASA third-country-operator authorisation in addition to lease approval. A wet lease is not a way to bypass operating bans or lower safety standards.
National economic licensing rules may restrict duration or require the lessee to demonstrate exceptional need. Regulators also consider protection of local employment and fair competition.
Why airlines use wet leases
Seasonal demand is a common reason. A leisure airline may need additional aircraft for a summer peak but not enough work to support them all year. ACMI capacity can be contracted for a defined season.
Delivery delays create another need. If an airline’s new aircraft arrives late, a wet lease can protect planned routes and slots. Engine or supply-chain problems may ground part of a fleet, requiring temporary replacement.
New airlines can use ACMI while building their own certification and crew base. Established airlines use it for route launches, special events, pilgrimage traffic, cargo peaks or recovery after disruption.
Why the lessor uses the model
An ACMI specialist earns revenue by supplying operational capacity rather than selling tickets. It may move aircraft between regions as seasons change. Northern-hemisphere summer demand can complement winter work elsewhere.
The lessor needs strong dispatch reliability, mobile crews and maintenance support. Aircraft utilisation drives revenue, so long ground periods are costly.
A diverse customer base reduces dependence on one airline but creates configuration and branding complexity. The lessor must adapt to different routes without changing the approved operation casually.
Commercial pricing
ACMI contracts are often priced per block hour, with a guaranteed minimum number of hours. Block time runs from movement off the departure stand to arrival on the destination stand.
The rate reflects aircraft capital cost, crew, maintenance, insurance and overhead. Fuel is usually excluded because the lessee controls route and schedule. Positioning flights, minimum daily utilisation and non-operation caused by the lessee are covered separately.
Escalation clauses address inflation, maintenance cost and exchange rates. Security deposits and payment guarantees protect the lessor.
A low headline rate can hide expensive minimum-hour commitments. The lessee compares total seasonal cost with cancellations, owning spare capacity or reducing schedule.
Aircraft configuration
The wet-leased aircraft may not match the lessee’s normal cabin. Seat pitch, business class, galleys, accessibility equipment and entertainment can differ.
Changing cabin configuration requires approved data, material and time. Short contracts often retain the lessor’s standard interior. Passengers must receive accurate product information.
Cargo capability also varies. A passenger aircraft may have different hold fire suppression, loading systems or dangerous-goods approvals. The lessee cannot sell capacity the operating aircraft is not approved to carry.
Livery and public identity
Some wet-leased aircraft retain the lessor’s colours. Others receive temporary titles, decals or a full repaint. Regardless of livery, booking information and airport displays should identify the operating carrier.
The operating carrier matters because its crew, procedures and AOC govern the flight. Consumer rules may require disclosure during booking.
A leased aircraft can create confusion during disruption if passengers contact the wrong airline. Customer-service plans define who handles rebooking, claims and baggage tracing.
Crew integration
Wet-lease crews may operate from a temporary base. They need local airport briefings, security access, transport and accommodation. Fatigue rules remain those of the approved operator and applicable authority.
If lessee cabin crew work with lessor pilots, procedures must be harmonised. Commands, emergency communication, door operation and sterile-cockpit rules cannot be assumed identical.
Language proficiency is essential. Crew resource management depends on clear communication during normal and abnormal events.
The lessee may provide customer-service training, but it cannot replace the lessor’s safety manuals.
Maintenance away from home base
The lessor arranges approved line maintenance at operating stations. This may use contracted organisations. Engineers need access to current maintenance data, tooling, parts and technical control.
A minor defect can become a long delay if no qualified engineer or spare is available. Contracts define response times and recovery obligations.
Minimum equipment list decisions belong to the operating carrier. The lessor’s approved MEL applies, even if the lessee’s own fleet allows a different dispatch condition.
Spare aircraft and substitution
ACMI specialists may offer substitute aircraft after a defect. Substitution protects the schedule but can change capacity or performance.
The replacement must be approved for the route and accepted under the lease. Slots, overflight permits and passenger information may need amendment.
A contract with no realistic substitution plan may provide less resilience than expected. The lessee assesses the lessor’s fleet size and spare ratio.
Safety oversight and audits
The lessee has a commercial and reputational interest in the lessor’s safety. It reviews AOC status, audit findings, insurance, incident history and operational capability.
In code-share or branded operations, regulations may require ongoing monitoring of partner compliance. IOSA or other audits can provide evidence but do not replace regulatory oversight.
The lessor must report occurrences through its approved system. Information-sharing clauses help the lessee manage network and customer impact without interfering with safety investigation.
Flight planning and dispatch
The lessor’s dispatch system prepares operational flight plans using the actual aircraft configuration and performance. The lessee supplies schedule, payload forecast and commercial priorities.
A route familiar to the lessee may be new to the lessor. Airport qualification, terrain, cold weather, ETOPS or dangerous-goods requirements must be confirmed.
Performance differences can reduce payload on hot days or short runways. The contract should not assume identical capability merely because both aircraft have similar seat counts.
Airport slots and traffic rights
Wet leasing does not create traffic rights. Bilateral agreements and operating permits may define which carrier may operate.
Authorities can require notification or approval when the operating carrier changes. A route announced under the lessee’s brand may be delayed if paperwork is incomplete.
Airport slots are coordinated around flight number, operator and aircraft characteristics. A last-minute substitution may need confirmation, especially for noise or size limits.
Passenger compensation and care
When a wet-leased flight is delayed, passenger rights can involve the contracting carrier, operating carrier or both depending on law. The commercial agreement should allocate cost without reducing passenger entitlements.
Airport staff need clear authority to issue meals, hotels and rebooking. Waiting for two control centres to debate responsibility worsens disruption.
Claims teams should know the aircraft was wet leased and retain records of the operating cause.
Baggage and ground handling
The lessee normally contracts ground handling, but the lessor must accept the procedures under its operations system. Load control must use the lessor’s approved weight-and-balance data.
Baggage reconciliation, dangerous goods and live animals require operator approval. A handler familiar with the lessee’s fleet may need training for different doors, holds or loading limits.
Communication between load controller and commander follows the operating carrier’s documentation.
Insurance and liability
Aircraft hull insurance protects the asset. Liability insurance addresses passengers, cargo and third parties. Contracts specify limits, deductibles and additional insured parties.
War-risk coverage and operations in higher-risk regions need attention. A route change can affect policy validity.
Insurance does not decide operational responsibility. It provides financial protection after an event, while regulation and contract define duties.
When wet leasing becomes risky
A weak lessor can create more disruption than it solves. Warning signs include a very small fleet, poor spare support, unstable crew rosters, repeated maintenance delays or unclear regulatory status.
Rapid expansion can strain training and oversight. The lessee should verify that promised aircraft and crews actually exist and are not committed elsewhere.
Dependence on ACMI for core year-round flying can also become expensive. The airline may lack control over product and long-term capacity.
Transition into service
A successful start requires a joint implementation plan. It covers approvals, manuals, routes, airport access, training, livery, IT messages, baggage, customer communication and emergency response.
Test flights or proving sectors may be needed. Schedule systems must display the operating carrier correctly. Crew hotels and transport must be ready before the first arrival.
The transition period is where small assumptions become operational failures. Detailed responsibility matrices reduce gaps.
End of lease
At contract end, the lessor repositions the aircraft and crews. The lessee removes branding and closes permits.
Outstanding defects, cabin damage and records are reconciled. Payment is adjusted for guaranteed hours and additional costs.
If the lessee’s replacement aircraft is late, extension negotiations may be expensive because the lessor may have another seasonal commitment.
Conclusion
Wet leasing is the purchase of operational capacity, not merely an aircraft. The lessor supplies the aeroplane, crew, maintenance and insurance and operates under its AOC. The lessee supplies the network, customers and many variable costs.
The model can protect schedules, cover seasonal peaks and bridge delivery delays. Its effectiveness depends on regulatory approval, clear operational control, compatible aircraft, maintenance support and a detailed contract. When those elements are strong, ACMI can add capacity in weeks. When they are weak, the airline has outsourced the aircraft but retained every consequence of its failure.
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