The period between 1947 and 1980 represented the consolidation of international air law, and the decades that followed marked the beginning of a new stage in its evolution: the modernization of the system. The growth of air transport, the globalization of markets, and the steady increase in international air traffic compelled the international community to strengthen two essential elements of the aviation system: the oversight of operational safety and the updating of the legal framework governing air transport.
As aviation continued to expand, the need for cooperation among States became increasingly evident. Aviation jurist Michael Milde summarized this reality by noting that “international civil aviation can function only through a high degree of cooperation among States and a common acceptance of uniform rules.” This principle reflects the spirit of the system established by the Chicago Convention.
By the end of the twentieth century, one of the most important challenges was ensuring that States properly implemented the Standards and Recommended Practices (SARPs) contained in the Annexes to the Chicago Convention. Although these standards had existed since 1944, for decades there had been no international mechanism capable of systematically evaluating how effectively States were implementing them.
To address this issue, the International Civil Aviation Organization (ICAO) launched in 1999 the Universal Safety Oversight Audit Programme (USOAP). This program introduced an international system of audits designed to assess the ability of States to oversee the safety of their civil aviation systems.
The USOAP strengthened compliance with Article 37 of the Chicago Convention, helped identify regulatory deficiencies before they could become operational risks, and promoted greater regulatory harmonization among States. In doing so, ICAO reinforced its role as a guardian of the safe and orderly development of international civil aviation.
At the same time, another key area of international air law also required modernization. For much of the twentieth century, the liability of air carriers had been governed by the Warsaw Convention of 1929 and its subsequent protocols. However, as air transport expanded, the compensation limits and documentation procedures established decades earlier began to prove insufficient.
To address these limitations, the International Conference on Air Law was convened in Montreal in 1999. Its outcome was the adoption of the Montreal Convention of 1999, an international legal instrument that modernized the legal regime governing international air transport and replaced the complex system of treaties derived from the Warsaw Convention.
The new Convention introduced a two-tier liability system in cases involving the death or injury of passengers. It also allowed the use of electronic documentation for passengers, baggage, and cargo, adapting the legal framework to the technological realities of modern aviation. Initially signed by 52 ICAO Member States on May 28, 1999, the Convention entered into force on November 4, 2003, establishing a more modern and balanced legal regime for international air transport.
In this way, the creation of the USOAP and the adoption of the Montreal Convention of 1999 were not merely technical reforms. They represented responses to an increasingly evident reality: a global air transport system also requires a legal framework capable of adapting, strengthening, and maintaining coherence in the face of the industry’s constant evolution. Through these developments, international air law entered the twenty-first century with new tools to support an aviation system that was becoming ever more interconnected.