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 World War II to establish the legal and institutional foundations for international civil aviation in the postwar era.

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. It regulates matters such as air navigation, flight rights, scheduled and non-scheduled air services, the nationality of aircraft, 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 postwar civil aviation; in the decades that followed, the development of international civil aviation was largely shaped under the framework of this Convention and ICAO.

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

1) Provisional International Civil Aviation Agreement (the provisional arrangement underlying 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 flight freedoms),

4) International Air Transport Agreement (the air transport agreement regulating five fundamental traffic freedoms); 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 codifies two fundamental flight freedoms granted by contracting states to each other:

1) The right to fly over a state’s territory without landing,

2) The right to make non-commercial landings (e.g., for technical reasons) in another state’s territory.

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 the additional three include the rights to carry passengers and cargo to a foreign country, to pick up passengers and cargo from a foreign country, and to carry passengers and cargo between two foreign countries provided the flight stops in the carrier’s own country. However, the fifth freedom (commercial carriage between two foreign countries without touching the carrier’s home country) has been viewed as sensitive by many countries and remains limited in application.

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

The Chicago Convention establishes 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 airspace. Article 1 of the Convention explicitly recognizes that contracting states have complete sovereignty over the airspace above their territories. Under this principle, foreign civil aircraft may not enter or fly over a state’s airspace without its permission. In contrast, 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, over areas outside national airspace (e.g., over open oceans), freedom of flight is the norm and these areas are open to all states.

The Chicago Convention distinguishes between national and international airspace and also categorizes aircraft as either “state aircraft” or civil aircraft. According to Article 3 of the Convention, the provisions of the Convention apply exclusively to civil aircraft; state aircraft are excluded. 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 with a special agreement or permission; otherwise, their flight over another state’s territory is prohibited. Furthermore, states have committed to taking into account 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 affirming state sovereignty, the Convention also includes provisions to prevent its abuse. Article 4 of the Convention stipulates that contracting states shall not use civil aviation for purposes inconsistent with the aims of the Convention. Thus, a legal barrier is established against the use of civil aircraft or civil aviation facilities for hostile purposes such as espionage or provocation against another state. This principle ensures that civil aviation is used exclusively for peaceful and secure purposes.

The Chicago Convention defines certain flight regime restrictions and sovereignty rights when states open their airspace for use. The foremost of these is the cabotage right. Cabotage means that the exclusive right to carry passengers, cargo or mail between two points within a country’s territory belongs solely to aircraft registered in that country. Article 7 of the Convention explicitly grants each state the right to refuse permission to foreign aircraft to operate commercial transport services between two points within its territory. For example, in Türkiye, only Turkish-registered aircraft may carry out commercial flights on domestic routes. The Convention further stipulates that if a state grants cabotage rights to a foreign state, it cannot do so as a privileged unilateral concession. 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 right of states to designate restricted or prohibited zones within their airspace. Article 9 of the Convention recognizes the right of each state to restrict or completely prohibit foreign civil aircraft from flying over certain areas of its territory for military requirements or public safety reasons. However, the exercise of this right is subject to certain conditions: prohibited zones must not be unnecessarily extensive and must be kept within reasonable limits to avoid undue disruption of international air traffic. Moreover, these prohibited zones and their coordinates must be communicated in advance to other states and to ICAO whenever possible. This ensures transparency for international aviation safety and planning.

States also retain the right to temporarily and 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. For instance, 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 of non-discrimination in the exceptional use of sovereignty rights. Additionally, 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 also distinguishes between scheduled and non-scheduled flights. Non-scheduled (irregular) international flights may overfly other states’ territories or make technical landings without prior permission (Article 5). In contrast, scheduled international flights require prior specific authorization or approval from the relevant state (Article 6). This distinction allows planned commercial air services to be regulated by sovereign states while preserving flexibility for ad hoc operations. Ultimately, the Chicago Convention, through its flight regime provisions, affirms the absolute rights of states over their airspace while balancing necessary freedoms and restrictions to ensure the safe and orderly flow of international air traffic.

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 Article 29 of the Convention, every aircraft engaged in international flight must carry the following documents:

• Registration certificate (aircraft registration certificate)
• Airworthiness certificate (airworthiness certificate)
• License for each member of the flight crew (appropriate licenses for the pilot and required crew members)
• Flight log (onboard journal) – aircraft’s flight record book
• Radio station license (if the aircraft is equipped with a radio transmitter – license for the onboard radio equipment)
• Passenger list (if carrying passengers, a list showing names and boarding/alighting points)
• Cargo manifest and declaration (if carrying cargo, a manifest and customs declaration detailing the cargo)

These documents facilitate international flight safety and oversight by documenting the aircraft’s legal status, technical airworthiness, and flight content. For example, the registration certificate identifies the state of registration and nationality of the aircraft, while the airworthiness certificate ensures its technical safety for flight.

Flight crew licenses attest to the competence of the pilot and crew. Passenger and cargo lists are required for potential customs, security and border control procedures. The consistent carriage of these documents serves as proof that each aircraft operates in compliance with international standards. The Chicago Convention also includes provisions for the mutual recognition of crew licenses and airworthiness certificates (Article 33) – 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 certificate. All these arrangements serve the purpose of establishing common rules for the safety and documentation of international civil aviation.

One of the most important innovations introduced by the Chicago Convention is the creation of an annex system for the detailed regulation of technical matters. The Convention text provides the overall 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 of annexes 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 encouraged but not mandatory. Article 37 of the Chicago Convention requires contracting states to make every effort to cooperate and harmonize standards on all technical matters necessary to improve the safety and regularity of air navigation. Under this article, ICAO has the authority to establish international standards and procedures in addition to the Convention. All such standards are published by the Council as annexes and submitted to member states for implementation.

Although standards are binding, it is not always practically feasible for all states to implement every standard immediately. To address this, Article 38 of the Chicago Convention provides a special mechanism: if a state cannot fully implement an accepted international standard or cannot fully align its own regulations with it, it is obligated to notify ICAO of the discrepancy or difference. This notification is commonly referred to as a “difference” notification. Thus, ICAO records which states are not fully compliant with which standards and what alternative practices they apply, ensuring that other states are informed. This mechanism provides both flexibility and transparency and security, because 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 to reflect the evolving needs and threats to civil aviation. Particularly after the 11 September 2001 terrorist attacks, significant updates were made in the field of aviation security. In 2002, ICAO adopted major revisions and additions to Annex 17 (Security: Protection Against Unlawful Interference). These changes made it mandatory to apply many security measures previously required only for international flights to domestic flights as well. For example, passenger and baggage screening, cockpit security, and pre-flight identity checks are now implemented on domestic flights in accordance with international standards. Airport security procedures were also tightened, and states’ national security programs were opened to ICAO inspections. Thus, while respecting the principle of sovereignty, minimum baseline security standards were ensured even in the domestic civil aviation activities of all contracting states. This was the international aviation community’s collective response to the global terrorist threat following 9/11. Similarly, with the strengthening of the safety management concept in the 2010s, Annex 19 (Safety Management Systems) was adopted to establish proactive risk management and reporting culture as international standards.

The original text of the Chicago Convention underwent no major substantive changes for many years after its signing in 1944, only minor institutional amendments. The first comprehensive substantive amendment, 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 and introduced a significant innovation regarding the sharing of responsibilities between the state of registry and the state of operation in situations such as aircraft leasing and change of operator.

The purpose of the 83 bis Protocol is to allow the temporary transfer of certain safety and oversight responsibilities from the state of registry to the state of operation when the two are different. 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 rules, all safety oversight obligations remain with the state of registry (e.g., maintenance inspections, airworthiness, validity of crew licenses, etc.). However, since the actual operation of the aircraft is under the supervision of another state’s civil 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 responsibilities under certain articles of the Convention to the operator state. 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, through an 83 bis agreement, Türkiye may transfer responsibility for maintenance and safety inspections to the lessee country’s civil aviation authority; conversely, the oversight of a foreign-registered aircraft may be delegated to Türkiye.

The operation of 83 bis is straightforward: a bilateral “83 bis agreement” between the contracting states defines the responsibilities to be transferred and is notified to ICAO. This agreement remains in force only for the duration of the lease or operational arrangement and terminates automatically upon its expiry. During the agreement period, the operator state assumes the role of the registry state for the specified safety oversight functions, such as renewing airworthiness certificates, ensuring the validity of pilot licenses, and conducting operational inspections. The registry state temporarily relinquishes responsibility for these functions. The aircraft’s registration (nationality) remains unchanged; it continues to bear the nationality of the registry state, but certain functional oversight duties are carried out by the other 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 it allows operations to proceed without requiring the aircraft to be deregistered from its foreign registry. The Protocol offers states this solution to support flexible commercial practices in aviation.

Türkiye is among the earliest states to become a party to the 83 bis Protocol. On 8 May 1991, the Grand National Assembly of Türkiye approved the 83 bis amendment through Law No. 3738; the Council of Ministers ratified it on 6 August 1992. Thus, the Protocol entered into force for Türkiye, and necessary domestic regulatory adjustments were made. Türkiye’s accession opened the way for the transfer, via 83 bis agreements, of obligations normally assigned to the state of registry (e.g., flight rules and safety inspections) to Türkiye when foreign-registered aircraft are leased to Turkish companies. Indeed, the General Directorate of Civil Aviation (SHGM) issued a directive to define implementation principles. The Regulation on Procedures and Principles of Aircraft Leasing (SHT-Leasing) details how 83 bis leasing arrangements are to be conducted under domestic law. This regulation also explicitly prohibits foreign-registered aircraft leased under 83 bis from operating domestic cabotage flights in 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 not permitted on foreign-registered aircraft. This regulation, by addressing such details, ensures the effective implementation of the 83 bis Protocol in Türkiye.

Today, the 83 bis Protocol is widely accepted internationally. More than 170 countries have become parties to this amendment . 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 registry state while enhancing the operator state’s oversight capacity 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 cooperation in international aviation law.

Since becoming a party to the Chicago Convention in 1945, Türkiye has implemented various domestic regulatory measures 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 (SHGM), established in 2005 by Law No. 5431 , 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 Directive 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 directive derives its legal basis from Law No. 4749 ratifying the Chicago Convention, Law No. 2920 on Civil Aviation, and the law establishing SHGM, thereby anchoring it firmly within the legal hierarchy.

According to the SHT-ICAO directive, every new ICAO standard or amendment is transmitted to the relevant unit within SHGM. The responsible unit evaluates the feasibility of implementing the change in Türkiye, consulting stakeholders if necessary. If direct implementation is not feasible or if objections arise, an official form is completed and a justified notification is submitted to ICAO. 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 notify ICAO of any difficulties or discrepancies encountered when implementing new ICAO standards. Thus, the obligation under Article 38 of the Convention to submit a “difference” notification is fulfilled through a modern system.

Another critical dimension of the directive 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 directive requires that when Türkiye enacts new legislation, the responsible 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 directive also regulates coordination mechanisms between these units and approval procedures by senior management to ensure that ICAO amendments are promptly incorporated into domestic legislation. Additionally, any new national aviation regulation must be reviewed by SHGM for compliance with ICAO standards before publication.