Chicago Convention

The Chicago Convention, officially known as the Convention on International Civil Aviation, is a multilateral international treaty adopted on 7 December 1944 at the International Civil Aviation Conference held in Chicago, United States of America, during the final phase of the Second World War, to establish the legal and institutional foundations for international civil aviation in the post-war period.

The Convention establishes fundamental principles for the safe, orderly, and sustainable conduct of international civil aviation, based on the principle of full and exclusive sovereignty of states over their own airspace. These principles cover air navigation, flight rights, scheduled and non-scheduled air services, aircraft nationality, mutual recognition of licenses and documents, and the harmonization of technical and operational standards for safety and security.

Due to the time required for states to complete their ratification processes, a provisional institutional structure, the Provisional International Civil Aviation Organization (PICAO), was established in 1945. Upon reaching the required number of ratifications, the Convention entered into force in March 1947, and as of April 1947, the International Civil Aviation Organization (ICAO) began operations as a permanent specialized agency.

This development is regarded as the beginning of a new era in civil aviation law. Indeed, the entry into force of the Chicago Convention marked a pivotal moment in post-war civil aviation; the subsequent development of international civil aviation was largely shaped under the framework of this treaty and ICAO.

Structure of the Convention

The outcome of the Chicago Conference consists not of a single text but of four interrelated primary agreements and a Final Act. These are, respectively:

1) Provisional Agreement on International Civil Aviation (the provisional arrangement establishing PICAO),

2) Convention on International Civil Aviation (the main text known as the Chicago Convention),

3) International Air Services Transit Agreement (the transit agreement recognizing two fundamental freedoms of the air),

4) International Air Transport Agreement (the air transport agreement regulating five fundamental freedoms of the air); the Chicago Conference Final Act is the document that brings these agreements together.

The Chicago Convention is recognized as the principal agreement within this group, with the others serving as complementary instruments. The Provisional Agreement functioned until the permanent agreement entered into force in 1945; the Final Act contains the conference’s decisions and recommendations.

The Transit Agreement legally establishes the two fundamental freedoms of the air granted by contracting states to each other:

1) The right to fly over a country’s airspace without landing,

2) The right to land for non-commercial purposes (e.g., technical stops).

The Air Transport Agreement grants a total of five freedoms for scheduled international flights; the first two freedoms are identical to those in the Transit Agreement, and it additionally includes the rights to: disembark passengers or cargo in a foreign country, embark passengers or cargo from a foreign country, and carry passengers or cargo between two foreign countries provided the flight originates or terminates in the carrier’s own country. However, the fifth freedom (commercial carriage between two foreign countries without touching the carrier’s own country) has been regarded as sensitive by many countries and remains limited in application.

Türkiye ratified all four agreements and the Final Act through Law No. 4749 in 1945, but granted the government authority to apply the fifth freedom temporarily and conditionally through bilateral agreements.

Legal Principles

The Chicago Convention establishes the fundamental legal principles governing civil aviation activities, balancing state sovereignty with international aviation operations. The foremost principle is the full and exclusive sovereignty of states over their own national airspace. Under Article 1 of the agreement, the contracting states explicitly acknowledge that they have full sovereignty over the airspace above their countries.^【1】 Under this principle, foreign civil aircraft may not enter or operate within a state’s airspace without its permission. Conversely, under the concept of international airspace, the principle of free flight applies over areas not under the sovereignty of any state, such as the high seas. Thus, outside national airspace (e.g., over open oceans), freedom of flight is the norm, and these areas are open to all states’ aircraft.

The Chicago Convention distinguishes between national and international airspace and also categorizes aircraft as either “state aircraft” or “civil aircraft.” Article 3 of the contract^【2】 According to the Convention, its provisions apply exclusively to civil aircraft; state aircraft are excluded from its scope. The term “state aircraft” refers to aircraft used for military, customs, or police services. Such state aircraft may enter or overfly another state’s territory only under a special agreement or with specific permission; otherwise, their operation within another state’s territory is prohibited. Furthermore, states have committed to consider the safety of civil aviation when regulating their own military and state flights. These provisions clearly delineate the distinction between civil and state aviation, aiming to ensure the peaceful and orderly development of civil flights.

While the Chicago Convention emphasizes state sovereignty, it also includes provisions to prevent its abuse. Article 4 of the treaty states that the contracting states agree not to use civil aviation for purposes inconsistent with the objectives of the treaty.^【3】 Thus, legal safeguards are established to prevent a state from using civil aircraft or civil aviation facilities for purposes such as espionage or provocation against another country. This principle ensures the peaceful and secure use of civil aviation.

Flight Regimes

The Chicago Convention defines certain flight regime restrictions and sovereignty rights when states open their airspace for use. The foremost of these is the right of cabotage. Cabotage refers to the exclusive right of a state to carry passengers, cargo, or mail between two points within its own territory using only its own registered aircraft. Article 7 of the agreement clearly grants each state the right to refuse to allow foreign state aircraft to carry out transportation between two points within its own country in exchange for payment or rent.^【4】 For example, in Türkiye, only Turkish-registered aircraft may conduct commercial operations on domestic routes (intra-country flights). The Chicago Convention further stipulates that if a state grants cabotage rights to a foreign state, it cannot offer this as a unilateral privilege. No state may establish a de facto monopoly by granting cabotage rights exclusively to one foreign state or one foreign airline. This regulation aims to preserve competitive equality in cabotage and prevent unfair competition.

Another critical flight regime issue is the authority of states to designate restricted airspace zones (prohibited areas) within their own airspace. Article 9 of the agreement recognizes the right of each state to restrict or completely prohibit the flight of foreign civil aircraft over certain areas of its territory due to military requirements or public security reasons.^【5】 However, the exercise of this right is subject to certain conditions: prohibited areas must not be unnecessarily extensive and must be kept within reasonable limits to avoid unjustifiably obstructing international air traffic. Additionally, these prohibited areas and their coordinates must be communicated in advance to other states and to ICAO whenever possible. This ensures transparency for the safety and planning of international aviation.

States also retain the right to temporarily or exceptionally close all or part of their airspace in emergency situations (e.g., during war or imminent national security threats). Such emergency restrictions must be applied without discrimination to all foreign aircraft. That is, if a country closes its airspace due to an imminent terrorist threat, the closure applies to all foreign aircraft (except its own). This demonstrates the principle that the exceptional use of sovereignty must be non-discriminatory. Furthermore, the Convention provides that if a foreign aircraft enters a prohibited zone, the relevant state may compel it to land at the nearest suitable airport. All these provisions grant contracting states the authority to control their airspace for national security purposes while ensuring that international air traffic is disrupted as little as possible.

The Chicago Convention distinguishes between scheduled and non-scheduled flights. Non-scheduled (irregular) international flights may transit through or make technical landings in other states’ territories without prior permission (Article 5^【6】). In contrast, scheduled international flights require prior specific authorization from the relevant state (Article 6^【7】). This distinction allows planned commercial air services to be regulated by sovereign states while still permitting flexibility for irregular operations. Ultimately, the Chicago Convention, through its provisions on flight regimes, affirms the absolute rights of states over their airspace while balancing them with necessary freedoms and restrictions to ensure the safe and orderly flow of international air traffic.

Safety and Documentation

The Chicago Convention imposes mandatory requirements for civil aircraft to carry a set of documents and certificates to ensure the safe and orderly conduct of international flights. According to According to Article 29^【8】, the following documents must be carried on every aircraft engaged in international flight:

• Registration certificate (aircraft registration certificate)
• Airworthiness certificate
• Licenses for each member of the flight crew (valid licenses for pilots and required crew members)
• Flight logbook (aircraft’s journey record)
• Radio station license (if the aircraft is equipped with a radio transmitter)
• Passenger list (if carrying passengers, listing names and boarding/alighting points)
• Manifest and customs declaration for cargo (if carrying cargo, detailing the transported goods)

These documents verify the legal status, technical airworthiness, and operational content of the flight, facilitating international flight safety and oversight. For example, the registration certificate identifies the state of nationality of the aircraft, while the airworthiness certificate ensures its technical safety for flight.

Crew licenses attest to the competence of pilots and crew. Passenger and cargo lists are required for potential customs, security, and border control procedures. The complete carriage of these documents serves as proof that each aircraft operates in accordance with international standards. The Chicago Convention also includes provisions on the mutual recognition of crew licenses and airworthiness certificates (Article 33^【9】), establishing the principle that valid certificates issued by one state shall be recognized by other contracting states. However, a state may refuse to accept a certificate that does not meet ICAO standards and may take into account any restrictive annotations on the document. All these arrangements serve the purpose of subjecting international civil aviation safety and documentation to common rules.

Annex System

One of the most important innovations introduced by the Chicago Convention is the establishment of an annex system for the detailed regulation of technical matters. The Convention text provides the general framework, while detailed technical standards are established in annexes published by ICAO. A total of 18 main annexes have been developed to cover standards and recommended practices across various areas of civil aviation. (The number has since increased to 19 through additions; for example, Annex 19 on Safety Management Systems was adopted in 2013.) These annexes detail numerous topics, beginning with titles such as Personnel Licensing (Annex 1), Air Rules (Annex 2), Meteorological Services (Annex 3), and Aeronautical Charts (Annex 4), and extending to airports, air navigation facilities, flight safety, security, and environmental measures. Each annex contains a comprehensive set of Standards and Recommended Practices (SARPs). Standards are binding technical rules, while Recommended Practices are flexible guidelines that are advised but not mandatory. The Chicago Convention Article 37^【10】 commits contracting states to cooperate to the maximum extent possible and harmonize standards on all technical issues necessary for the safety and regularity of air navigation. Under this article, ICAO has the authority to establish international standards and procedures beyond the Convention. All such standards are published by the Council as annexes and submitted for implementation by member states.

Although standards are binding, it is not always practically feasible for all states to implement every standard immediately. To address this, the Chicago Convention Article 38^【11】 provides a special mechanism: if a state cannot fully implement an adopted international standard or cannot fully align its own regulations with it, it is obligated to notify ICAO of this discrepancy or deviation. This notification is commonly referred to as a “difference” notification. Thus, ICAO records which states do not comply with which standards or what alternative practices they apply, and informs other states. This mechanism provides both flexibility and transparency and security, as a state that does not comply with a standard formally declares it rather than concealing it.

ICAO’s annex system has been updated over the years in response to the evolving needs and threats in civil aviation. Particularly after the terrorist attacks of 11 September 2001, significant updates were made in the field of aviation security. In 2002, ICAO Appendix 17 (Security: Protection Against Unlawful Interference)^【12】 adopted major amendments and additions. These changes made many security measures previously required only for international flights mandatory for domestic flights as well. For instance, passenger and baggage screening, cockpit security, and pre-flight identity checks began to be implemented domestically in accordance with international standards. Additionally, airport security procedures were tightened, and states’ national security programs were opened to ICAO inspections. Thus, without compromising the principle of sovereignty, all contracting states were required to maintain certain minimum security standards even in their domestic civil aviation activities. This was the international aviation community’s collective response to the global terrorist threat following 9/11. Similarly, as the safety management concept strengthened in the 2010s, Appendix 19 (Security Management System)^【13】 proactive risk management and reporting culture were established as international standards.

Protocol 83 bis

The original text of the Chicago Convention remained largely unchanged for many years after its signing in 1944, undergoing only minor institutional amendments. The first comprehensive substantive change, Article 83 bis, was adopted by the ICAO Assembly in 1980, opened for signature, and entered into force on 20 June 1997 after sufficient ratifications. This amendment added a new article titled 83 bis to the Chicago Convention, introducing a significant innovation regarding the sharing of responsibilities between the state of registry and the state of operation in cases such as aircraft leasing or change of operator.

The purpose of the 83 bis Protocol is to allow, in situations where the state of registry and the state of actual operation of an aircraft differ, for certain safety and oversight responsibilities to be temporarily transferred from the state of registry to the state of operation. In the airline industry, operational leasing (dry lease), joint operations, or exchange arrangements are common: an aircraft registered in one state may be operated by an airline from another state. Under normal Chicago Convention provisions, all safety and oversight obligations remain with the state of registry (e.g., maintenance inspections, airworthiness, validity of crew licenses). However, since the actual operation of the aircraft is under the supervision of another state’s aviation authority, a gap or confusion in oversight may arise. Article 83 bis addresses this issue by granting contracting states the authority to enter into bilateral agreements to transfer specific oversight functions. Accordingly, the state of registry and the state of operation may, through a written agreement, transfer all or part of the obligations under specific articles of the Convention to the state of operation. In particular, obligations under Article 12 (Application of flight rules), Article 30 (Radio equipment on aircraft), Article 31 (Airworthiness certificates), and Article 32(a) (Crew licenses) may be transferred in this manner. For example, if a Turkish-registered aircraft is leased to a foreign airline, under an 83 bis agreement, Türkiye may transfer responsibility for maintenance and safety inspections to the lessee state’s civil aviation authority; conversely, the oversight of a foreign-registered aircraft may be delegated to Türkiye.^【14】

The operation of 83 bis is straightforward: bilateral “83 bis agreements” between contracting states define the responsibilities to be transferred and are notified to ICAO. These agreements remain in force only for the duration of the lease or operational arrangement and terminate automatically upon expiration. During the agreement period, the state of operation assumes the role of the state of registry for the specified safety oversight functions, such as renewing airworthiness certificates, ensuring pilot license validity, and conducting operational controls. The state of registry temporarily relinquishes responsibility for these functions. The aircraft’s registration (nationality) does not change; it continues to bear the nationality of its state of registry, but certain functional oversight duties are carried out by another state. Thus, 83 bis does not imply a transfer of legal sovereignty, but rather a sharing of operational oversight authority. The practical benefit of 83 bis is that aircraft can be operated without requiring removal from their foreign registry. The Protocol offers states this solution to support flexible commercial practices in aviation.

Türkiye is among the earliest countries to become a party to the 83 bis Protocol. On 8 May 1991, with Law No. 3738, the Grand National Assembly of Türkiye deemed it appropriate to approve Amendment 83 bis.^【15】 The Council of Ministers adopted the ratification decision on 6 August 1992. Thus, the Protocol entered into force for Türkiye, and necessary domestic regulations were enacted. Türkiye’s accession opened the way for obligations normally assigned to the state of registry—such as flight rules and safety inspections—to be transferred to Türkiye under 83 bis agreements for aircraft leased by Turkish companies from foreign registries. Indeed, the General Directorate of Civil Aviation (SHGM) issued an instruction to define implementation principles. The Regulation on Procedures and Principles of Aircraft Leasing (SHT-Leasing) details how 83 bis-related leasing arrangements are to be conducted under domestic law. This regulation further stipulates that aircraft leased from foreign registries under 83 bis may not conduct domestic cabotage flights within Türkiye. As a rule, although the aircraft does not need to be deregistered from its foreign registry, commercial flights between two points within Türkiye (cabotage) are prohibited for foreign-registered aircraft. This regulation, by addressing such details, ensures the effective implementation of the 83 bis Protocol within Türkiye.

Today, the 83 bis Protocol is widely accepted internationally. More than 170 countries have become parties to it.^【16】 Many countries use the 83 bis mechanism in their leasing agreements with foreign airlines to prevent gaps in flight safety oversight. Thanks to the Protocol, safety inspections of leased aircraft are seamlessly transferred to another authority, reducing bureaucratic burdens on the state of registry while enhancing the oversight capacity of the state of operation and ensuring flight safety. Ultimately, 83 bis is a significant innovation demonstrating the Chicago Convention’s ability to adapt to the changing aviation sector and is regarded as a practice that strengthens the spirit of international cooperation in aviation law.

Compliance and Oversight in Türkiye

Since becoming a party to the Chicago Convention in 1945, Türkiye has made various adjustments to its national legislation to ensure compliance with the Convention’s provisions and ICAO standards. The Turkish Civil Aviation Law No. 2920, which entered into force in 1983, reinforced the principles of the Chicago Convention in domestic law; the General Directorate of Civil Aviation (Law No. 5431^【17】), established in 2005, was structured as the authority responsible for implementing international aviation rules. Since compliance with ICAO Standards and Recommended Practices is a dynamic process, Türkiye has issued a specific administrative regulation titled SHT-ICAO to achieve this goal.

The SHT-ICAO (Implementation Instruction for the Chicago Convention and its Annexes) is a guiding regulation that defines the procedures and principles for incorporating changes and new standards issued by ICAO into Turkish legislation. Its purpose is to ensure timely integration of every newly accepted ICAO standard into Turkish regulations and to maintain continuous international compliance. The instruction derives its legal basis from Law No. 4749 approving the Chicago Convention, Law No. 2920 on Civil Aviation, and the founding law of SHGM, thereby establishing a solid legal foundation.

According to the SHT-ICAO instruction, every new standard change notification from ICAO is transmitted to the relevant responsible unit within SHGM. The responsible unit evaluates the feasibility of implementing the change in Türkiye, consulting sector stakeholders if necessary. If direct implementation of the new standard is not feasible or if objections exist, a formal justification is submitted to ICAO using the prescribed form. This notification process is now conducted through an information system called SMIS (Standards and Recommended Practices Management System). SMIS is an electronic system integrated with ICAO that enables countries to manage their compliance status and potential objections. Türkiye uses SMIS to electronically communicate to ICAO any difficulties or non-conformities encountered during the implementation of new ICAO standards. Thus, the obligation under Article 38 of the Convention for “difference notification” is fulfilled through a modern system.

Another critical dimension of the instruction is the use of the EFOD (Electronic Filing of Differences) system. EFOD is a global database that allows states to report online their compliance status with standards in the Convention annexes and any differences. The SHT-ICAO instruction mandates that when Türkiye makes legislative changes, the relevant unit must compare the new regulation with ICAO standards and report any existing differences to ICAO via EFOD. If the relevant annex has not yet been incorporated into EFOD, the notification is submitted through traditional written channels. The use of EFOD enables Türkiye, like all other ICAO members, to maintain up-to-date information on which standards it fully complies with and where it applies national differences. This contributes to mutual trust and the sharing of safety information in international civil aviation.

Within SHGM, specific units are assigned responsibility for implementing each ICAO annex (e.g., the Flight Standards Directorate for annexes related to flight safety, the Infrastructure Directorate for annexes related to airports). The SHT-ICAO instruction also regulates coordination mechanisms among these units and approval procedures by senior management to ensure that ICAO changes are incorporated into domestic legislation without delay. Additionally, any new national aviation regulation must be reviewed for compliance with ICAO standards within SHGM before publication.