Regarding the definition of an aircraft, two different systems are implemented across countries: the subjective system and the objective system. In subjective systems, the vehicles classified as aircraft are defined by "numerus clausus," meaning they are limited in number. In objective systems, once the definition of an aircraft is established, all vehicles fitting that description are considered aircraft. The critical aspect in objective systems is whether or not the vehicle meets the described characteristics.

Although contracts often do not provide an exact definition, Annexes 2 and 7 of the International Civil Aviation Convention broadly define aircraft as "any vehicle capable of deriving support in the atmosphere from air reactions, excluding air reactions against the earth's surface."

According to Article 68/A of the Turkish Civil Aviation Law No. 2920, the primary applicable provision is the "Cape Town Protocol," where an aircraft is defined as "airframes with aircraft engines installed or helicopters as defined in the Chicago Convention."

Under Article 3(b) of the Turkish Civil Aviation Law No. 2920, an aircraft is defined as any vehicle capable of taking off and navigating in the air. Two qualifications are essential according to this definition: the capability of taking off and the capability to navigate in the air. Other features are not considered essential elements.

Various classifications of aircraft exist, such as registered aircraft and non-registered aircraft. However, the most significant classification is civil aircraft and state aircraft. Civil aircraft fall under Turkish Civil Aviation Law (TSHK) and the International Civil Aviation Convention (MSHS), whereas state aircraft are excluded from these laws.

The key consequence of state aircraft being outside the scope of these laws is their exclusion from leasing transactions.

State aircraft are defined in Article 3(c) of the Turkish Civil Aviation Law No. 2920 as aircraft used by the state for military, security, customs, and firefighting services. Academic doctrine provides two views regarding identifying state aircraft. The first viewpoint argues that a vehicle must be state-owned to qualify as a state aircraft. The alternative viewpoint emphasizes the purpose of usage, disregarding ownership.

Civil aircraft are those not assigned for purposes specified for state aircraft.

Civil aircraft are categorized into Turkish civil aircraft and foreign civil aircraft.

As defined in Article 3(d) of the Turkish Civil Aviation Law No. 2920, Turkish civil aircraft are vehicles other than state aircraft whose ownership belongs to the Turkish state, public entities, or Turkish citizens.

Article 49 of the Turkish Civil Aviation Law, titled "Aircraft and Maintenance of Registries," specifies conditions under which aircraft owned by legal entities are regarded as Turkish civil aircraft:

Legal entities established under Turkish laws; a) Aircraft owned by professional public organizations, associations, political parties, unions, or foundations, provided the majority of the administrative body members are Turkish citizens; b) Aircraft owned by commercial companies, cooperatives, and their unions registered in the Turkish Trade Registry, provided the majority of authorized administrators and representatives are Turkish citizens and Turkish partners hold the voting majority according to the company’s articles of association.

Although a complete definition is not provided, foreign civil aircraft may be identified as vehicles outside the definition of state aircraft whose ownership does not belong to the Turkish state, public entities, or Turkish citizens.

The legal nature of aircraft is stipulated in Article 65 of Turkish Civil Aviation Law No. 2920, stating: "Unless otherwise provided by this Law, aircraft are subject to movable property regulations."

Thus, aircraft are classified as movable property and are governed by movable property provisions.

Each state deals with aircraft under its jurisdiction, granting specific privileges to those bearing its nationality. Turkish civil aircraft are considered under Turkish nationality, based on an ownership-centric definition. However, state aircraft consider assignment purposes rather than ownership. Therefore, a foreign aircraft used for relevant purposes can constitute a state aircraft outside Turkish nationality.

An aircraft is a composite structure composed of numerous parts, instruments, and devices.

Article 684 of the Turkish Civil Code defines integral parts as: "Integral part is the essential element of the primary object according to local customs, inseparable without destroying, damaging, or altering the object's structure."

Integral parts of aircraft include engine assemblies, wings, and landing gears. Without these integral parts, an aircraft loses its capability to navigate airspace, ceasing to be an aircraft.

Besides integral parts, aircraft also contain accessories. Accessories are movable items specifically assigned to the aircraft for operation, protection, or benefit. Examples include service carts and multimedia screens inside airplanes.

Aircraft lease agreements are regulated under Article 118 of Turkish Civil Aviation Law titled "Lease and Charter Agreements," stating: "If only the aircraft is leased without flight crew, relevant provisions of the Turkish Code of Obligations apply; if the aircraft is leased with the flight crew, either entirely or partially, or through a Charter Agreement, relevant provisions of the Turkish Commercial Code apply."

Besides references to the Turkish Code of Obligations and the Turkish Commercial Code, the Financial Leasing Law (FKK) also contains provisions concerning aircraft leases. Specifically, FKK Article 2/5 stipulates that aircraft, their engines, and related parts may be subject to financial leasing, warranting separate evaluations under FKK.

Due to the international and technically specialized nature of civil aviation, international treaties and regulations enforced by the Directorate General of Civil Aviation (SHGM) comprehensively govern aircraft leasing agreements. Therefore, analysis should commence with general legal regulations followed by international conventions and national regulations enacted by SHGM.

Lease agreements are defined in Article 299: "A lease agreement is a contract whereby the lessor transfers usage or usage and enjoyment of an object to the lessee, who, in return, undertakes to pay the agreed lease fee."

The three elements constituting lease agreements include the leased object, lease fee, and mutual consent.

Dry Lease is among the initial forms of aircraft lease agreements.

In this agreement, aircraft are leased to lessees without flight crew. The lessee assumes technical, operational, and commercial management. Throughout the lease period, maintenance, insurance, and operational costs belong to the lessee. Flight crew and related equipment must also be provided by the lessee. Under dry lease, aircraft operate under the lessee's operating license.

Two key features define a dry lease under national and international regulations:

1.     Aircraft lease without flight crew.

2.     Operation of leased aircraft under the lessee's operating license.

Wet lease involves leasing aircraft accompanied by flight crew provided by the lessor. Technical management remains with the lessor, whereas commercial management lies with the lessee. Aircraft operate under the lessor's operating license.

Typically, wet leases are short-term agreements.

Like dry leases, wet leases comprise two essential elements:

1.     Leasing aircraft along with flight crew.

Operating the leased aircraft under the lessor's operating license.