An Air Defense Identification Zone (ADIZ) is a unilaterally declared airspace, extending beyond sovereign territorial airspace (12 nautical miles), within which a state requires civil and military aircraft to identify themselves for national-security purposes. The concept has no codified basis in the Chicago Convention on International Civil Aviation (1944) or in the United Nations Convention on the Law of the Sea (UNCLOS); it rests on customary practice initiated by the United States in 1950. Taiwan's ADIZ was drawn by U.S. Pacific Command in the 1950s during the Cold War and notably overlaps portions of mainland Chinese territory, the Taiwan Strait median line, and waters near the Senkaku/Diaoyu Islands. The People's Republic of China declared its own East China Sea ADIZ on 23 November 2013, partially overlapping Taiwan's and Japan's zones. Incursions by People's Liberation Army Air Force (PLAAF) and PLA Navy aircraft into the southwestern quadrant of Taiwan's ADIZ have become the principal vehicle for Beijing's military signaling since 2020.
The mechanics of an incursion follow a recurring pattern. PLA aircraft — typically Shenyang J-16 multirole fighters, Xi'an H-6 bombers, Y-8 anti-submarine variants, KJ-500 airborne early warning platforms, and increasingly BZK-005 and TB-001 unmanned aerial vehicles — depart from bases in the Eastern and Southern Theater Commands, principally airfields in Fujian, Guangdong, and Zhejiang. They transit into the southwestern corner of Taiwan's ADIZ, an area between the Pratas (Dongsha) Islands and Taiwan's southern coast that lies outside PRC territorial airspace but within the zone Taipei monitors. Taiwan's Ministry of National Defense (MND) detects the sorties via the Leshan long-range early-warning radar on Mount Leshan and AN/FPS-115 PAVE PAWS systems, scrambles combat air patrol from F-16V and Mirage 2000-5 squadrons, issues radio warnings, and activates air-defense missile tracking. Since September 2020, the MND has published daily tallies of incursions, sortie composition, and tracks on its official website and Twitter/X feed.
Variants of the activity have evolved. Median-line crossings — penetrations of the unofficial centerline of the Taiwan Strait observed since 1955 — were rare before 2019 but became routine after August 2022, when Beijing declared the line no longer existed following U.S. House Speaker Nancy Pelosi's visit to Taipei. Encirclement sorties, in which aircraft enter the ADIZ from multiple azimuths simultaneously, debuted during the Joint Sword exercises of April 2023 and August 2022. Naval coordination is increasingly visible: PLAN surface action groups, including the Shandong and Liaoning carrier strike groups, operate east of Taiwan in coordinated air-sea displays. The Eastern Theater Command publishes its own communiqués through Xinhua and the PLA Daily, framing the sorties as "combat readiness patrols" (战备警巡) or "joint combat readiness patrols" (联合战备警巡).
Concrete escalation points are documentable. On 4 October 2021, 56 PLA aircraft entered the ADIZ in a single day, the largest pre-2022 incursion. The August 2022 Joint Sword exercises following Speaker Pelosi's visit involved live-fire drills in six zones surrounding Taiwan and ballistic missile overflights of the island. Joint Sword-2024A (May 2024) followed President Lai Ching-te's inauguration; Joint Sword-2024B (October 2024) responded to his National Day address. The Eastern Theater Command, headquartered in Nanjing under General Lin Xiangyang, has been the operational lead. Taiwan's MND under successive ministers — Chiu Kuo-cheng and Wellington Koo — has institutionalized the daily reporting cadence and accelerated procurement of F-16V Block 70 aircraft and indigenous Hsiung Feng and Tien Kung missile systems.
ADIZ incursions must be distinguished from violations of territorial airspace, which extends only 12 nautical miles from baselines under UNCLOS Article 2. No PLA crewed aircraft has crossed into Taiwan's territorial airspace in the contemporary period; the incursions are into a much larger advisory zone where international overflight is legally permissible. They also differ from freedom of navigation operations (FONOPs), which assert legal rights against excessive maritime claims, and from gray-zone coercion more broadly, which includes Coast Guard pressure, undersea cable incidents, and economic measures. The ADIZ framing is itself contested: Beijing rejects Taiwan's zone as a legacy of the Chinese Civil War and asserts that flights within China's own claimed airspace cannot constitute an "incursion."
Edge cases and controversies persist. A PLA Y-8 reportedly crossed briefly into airspace near Dongyin Island in February 2022, though Taipei characterized it as a near-violation rather than an entry. The shootdown question — whether Taiwan would engage PLA aircraft that crossed the 12-nautical-mile line — remains deliberately ambiguous; President Tsai Ing-wen authorized warning shots against unmanned aerial vehicles in August 2022, and Taiwan downed a civilian-origin drone over Lieyu on 1 September 2022. Critics within Taiwan's defense community argue that the daily tally normalizes Chinese presence and exhausts pilot flight hours and airframe lifespan on F-16s and Mirage 2000s, a concern that prompted Taipei to shift to ground-based radar tracking for lower-threat sorties beginning in 2023.
For the working practitioner, ADIZ incursion data constitutes the most granular open-source indicator of cross-strait military temperature available. Desk officers at the U.S. Department of State's Bureau of East Asian and Pacific Affairs, Japan's Ministry of Foreign Affairs China-Mongolia Division, and European foreign ministries treat MND daily releases as a primary signal. Sortie composition — particularly the appearance of H-6 bombers, refueling tankers, or carrier-borne J-15s — telegraphs operational ambition. Incursions function simultaneously as deterrence signaling, training under realistic conditions, intelligence collection on Taiwanese reaction times, and political messaging to domestic PRC audiences. Reading the pattern requires distinguishing routine patrols from exercise-linked surges keyed to Taiwanese elections, U.S. arms sale announcements, congressional delegations, and PRC political anniversaries.
Example
On 4 October 2021, Taiwan's Ministry of National Defense reported 56 People's Liberation Army aircraft — including J-16 fighters and H-6 bombers — entering the southwestern quadrant of Taiwan's ADIZ in a single day, then a record.