The Influence of the Philippine Archipelagic Sea Lanes Act on Navigation Rights

On November 9, 2024, Philippine president Ferdinand Marcos Jr. signed into law both the Philippine Maritime Zones Act and the Philippine Archipelagic Sea Lanes (ASL Act). Observers have been particularly focused on the Philippine Maritime Zones Act for intensifying the dispute between China and the Philippines, but it is the ASL Act that has broad implications for the navigation rights of countries in the Western Pacific.

According to the United Nations Convention on the Law of the Sea (UNCLOS), archipelagic waters refer to areas within archipelagic baselines drawn by archipelagic states on the landward side. Such states can designate sea lanes and air routes within these waters to enable foreign ships or aircraft to exercise the right of archipelagic sea lanes passage. This passage allows for the continuous and unobstructed transit of foreign vessels and aircraft, enabling the rights of navigation and overflight in a normal mode.

The Philippines, the second-largest archipelagic state after Indonesia, officially established archipelagic baselines in 1961. However, it had not designated archipelagic sea lanes until the introduction of the ASL Act, which establishes a passage system with three designated sea lanes for crossing Philippine archipelagic waters:

1. Philippine Sea - Balintang Channel - West Philippine Sea (South China Sea)
2. Celebes Sea - Sibutu Passage - Sulu Sea - Cuyo East Pass - Mindoro Strait - West Philippine Sea (South China Sea)
3. Celebes Sea - Basilan Strait - Sulu Sea - Nasubata Channel - Balabac Strait - West Philippine Sea (South China Sea)

The map of archipelagic sea lanes within Philippine waters. Red lanes indicate the three sea lanes designated by the ASL Act, while green lanes represent other straits excluded from the archipelagic sea lanes system. (Illustration by the author)

Outside of these designated archipelagic sea lanes, the ASL Act specifies that foreign vessels may only exercise innocent passage in Philippine archipelagic waters. However, innocent passage is a more restrictive form of navigation right compared to archipelagic sea lanes passage.

Under archipelagic sea lanes passage, foreign vessels and aircraft are permitted to transit in an unimpeded, continuous manner, and are allowed to navigate or overfly in their normal mode of operation without unnecessary interruptions. Archipelagic states are expected not to interfere with such passage and must publicly disclose any potential hazards to navigation or overflight within or above the sea lanes.

By contrast, innocent passage is limited to ships, excluding aircraft, and is subject to stricter provisions under UNCLOS, including regulations governing the purpose and manner of navigation as well as prohibited activities of vessels. Additionally, archipelagic states may suspend innocent passage for foreign vessels in their archipelagic waters if necessary to protect national security.

The ASL Act's most significant impact on foreign vessels and aircraft is the reduction in the number of straits eligible for archipelagic sea lanes designation. Philippine archipelagic waters contain multiple navigable straits allowing east-west and north-south passage through Philippine waters. The right of passage through these straits, first established as a legitimate navigational right by UNCLOS, has been historically exercised by states worldwide. Notably, several straits within Philippine waters served as strategic routes during pivotal naval battles in World War II. By excluding most of these straits from the archipelagic sea lanes system and instead imposing only innocent passage rights, the ASL Act restricts other countries' legitimate navigation rights.

From both a historical and current perspective, the following additional straits within Philippine archipelagic waters warrant designation as archipelagic sea lanes. In the north: Babuyan Channel; in the west: Verde Island Passage, Palawan Passage, and North Balabac Strait; in the east: San Bernardino Strait and Surigao Strait; and in the south: Sugbai Passage and Tapaan Passage.

Previously, in the absence of designated sea lanes or air routes, foreign vessels and aircraft could exercise archipelagic sea lanes passage in customary routes used for international navigation, as stipulated by UNCLOS. However, with the enactment of the ASL Act, foreign vessels are now restricted to the three prescribed sea lanes and may only exercise innocent passage in other straits within Philippine waters. This restriction constitutes a substantial reduction in global navigation rights in the Western Pacific.

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