Why can an aircraft not normally be registered in more than one country?

In air law, the principle that an aircraft cannot be validly registered in more than one state is a foundational requirement established by the 1919 Paris Convention and maintained by the 1944 Chicago Convention.1

This rule is of cardinal importance because registration determines an aircraft's nationality, which serves as the primary mechanism for assigning legal rights and duties. By ensuring every aircraft has a single state of registry, the international community guarantees that there is always a specific state answerable for the aircraft.1

This single-state registration is essential for regulatory oversight, as the state of registry is responsible for:
* Issuing or validating certificates of airworthiness.1
* Licensing operating personnel and flight crews.1
* Authorizing the installation and operation of radio transmitting apparatus.1
* Enforcing rules and investigating accidents, particularly over the high seas.1

While dual registration is precluded to maintain clear legal accountability, the ICAO Council has recognized the possibility of joint or international registration in specific circumstances.1