Though the People’s Republic of China (PRC) turned heads with the sheer number of ships it deployed in an unnamed December 2024 military exercise around Taiwan, its concurrent declaration of a vast area of restricted airspace along the Chinese coast stirred further questions. What was the PRC’s intention when it announced restrictions on aviation over a swathe of airspace stretching 1,000 kilometers from Shanghai to Guangdong Province? The PRC elevates the readiness of potential invasion forces by conducting exercises around Taiwan, but what would it gain by cordoning off airspace in regions hundreds of kilometers removed from its actual military drills?
Taiwan’s Ministry of Defense (MND, 國防部) was quick to label this action as an element of the PRC’s anti-access/area denial (A2/AD) strategy aimed not at Taiwan’s military, but rather Taipei’s partners such as the United States and Japan. PRC media and scholars were unusually tight-lipped about the December 2024 exercises, so there is little to be inferred from official sources. This article will attempt a forensic examination of the circumstances surrounding the December 2024 airspace reservations, in order to gain insights into the strategic rationale behind Beijing’s decision.
The Temporary Reserved Airspace Zones
Image: A map showing the location of the PRC’s seven declared reserved airspace zones (colored red) alongside the areas of PLA aircraft sorties (colored blue) during the December 9-11 military exercises. (Image source: Duan Dang)
While Taiwan’s Ministry of National Defense mistakenly announced that the reserved airspace had been declared by the People’s Liberation Army (PLA), notification of the aviation restrictions actually emerged from the air traffic control authority of the Shanghai flight information region (FIR). A FIR is a stretch of airspace over which one country’s air traffic control authority has the responsibility to communicate essential information such as inclement weather or military activity. It is not the same as sovereign airspace, which extends only 12 nautical miles beyond a country’s coastline. For example, the United States is responsible for flight information regions spanning half of the Pacific Ocean, far beyond its sovereign airspace. When an authority wishes to restrict aviation in a certain part of a FIR, they issue a Notice to Air Missions (NOTAM) through a centralized system managed by the United States’ Federal Aviation Administration. On December 8, the Shanghai air traffic control authority released a NOTAM—effective from December 9 to 11—outlining seven areas of restricted airspace along the Chinese coast. The next day, Taiwan’s MND publicly shared intelligence that the PLA had massed ships around Taiwan in anticipation of large-scale military exercises.
The airspace reservations announced in the Shanghai air traffic control’s NOTAM carried no name; it was Taiwan’s MND that christened them “temporary airspace reservation zones” (空域臨時保留區). The fact that the zones were announced by a civilian institution in the PRC, rather than the PLA, encouraged some in Taiwan to dispute that the reserved areas were germane to the military exercises. The strict timing of the reserved areas over the three days of large-scale military exercises belies this claim. Meanwhile, the seven reserved areas were constructed in a patchwork manner so as to avoid infringement over any civil aviation route. In fact, the author’s analysis of open-source data on civilian flight activity during the three days of the airspace reservations reveals little to no disruption of routine civil aviation activity. The charts below show the presence of commercial aircraft around Taiwan and the Chinese coast at the precise same time of day (13:00 CST) and day of the week (Monday) on November 25 and December 9.
Image: Maps showing civil activity at 13:00 CST on a Monday across two dates, November 25 and December 9, 2024. The PLA’s unnamed military exercises spanned December 9-11, 2024. (Image source: FlightRadar24)
Since the reserved airspaces were set in areas where commercial aircraft does not venture, there is no observable interruption in civilian air travel on December 9 as a result of the “temporary airspace reservation zones.” This suggests that the PRC’s airspace reservations may have been aimed instead at testing out restrictions intended to block potentially hostile military aviation—hostile aviation that might fly between civil aviation routes—during the PLA’s military exercises. This analysis aligns with the Taiwan MND’s assessment that the “temporary airspace reservation zones” were an element of the PRC’s broader A2/AD strategy.
Beijing’s A2/AD strategy is aimed at deterring military involvement by Taipei’s informal diplomatic partners, such as the United States and Japan, in an armed contingency related to Taiwan. In order to succeed at any kind of kinetic operation to coerce Taiwan into submission, the PLA must prevent Taiwan’s partners from mobilizing major military assets along the “First Island Chain” in the western Pacific. Such an operation would necessarily involve no-fly zones around Taiwan and the Chinese coast as well as the threat of lethal engagement with US-led forces via missile batteries, drones, and fighter planes. As shown in the map at the start of this section, the actual locations of People’s Liberation Army Air Force (PLAAF) sorties were concentrated in the immediate vicinity of Taiwan during the December 2024 exercises, while the reserved airspace zones extended far up the coast of China and tangentially to the First Island Chain. This arrangement suggests that the military exercises may have been a rehearsal of the theater-level operation required for a successful mission to capture Taiwan.
A Playbook of Airspace Restriction
On prior occasions, the PRC has experimented with airspace reservations and no-fly zones in contested areas in the East and South China Seas. In April 2023, the PRC caused consternation when it declared a three-day no-fly zone over a roughly 5,000 square kilometer stretch of airspace immediately north of Taiwan. The declaration, which Beijing shared directly with Taipei without issuance of a NOTAM, coincided with a flurry of weeks-long PLA military exercises. This no-fly zone did indeed infringe upon major civilian aviation routes routing through Taiwan, and would have disrupted 160 flights per day if the PRC government had not backed down and reduced the length of the no-fly zone from three days to just 27 minutes. The PRC’s ostensible rationale for the airspace closure was falling debris from a weather satellite launch. However, the initial attempt to close major civil aviation routes for 72 hours during a period of provocative military exercises belies this banal justification. At the time, some analysts—including this author—warned that this event could presage more provocative future airspace restrictions.
The April 2023 satellite launch was not the only instance in which the PRC has closed airspace in sensitive areas in association with rocket activity. In May 2023, the Civil Aviation Administration of China (CAAC, 中國民用航空局) notified the Civil Aviation Authority of the Philippines that three zones adjacent to the Scarborough Shoal might experience falling debris as a result of a PRC rocket launch and should be closed. Scarborough Shoal, a maritime feature controlled by the Philippines but claimed by the PRC, has been subject to a years-long pressure campaign by Beijing featuring repeated intrusions by Chinese vessels. The day after the rocket launch, a Philippines government spokesperson announced that they had not detected falling debris in the restricted zones near Scarborough Shoal.
While the so-called “temporary airspace reservation zones” associated with the PLA’s unnamed December 2024 military exercises were in effect, a Vietnamese journalist named Duan Dang pointed out that the PRC had restricted an overlapping swathe of airspace just weeks before the exercises. In November 2024, Shanghai air traffic control issued a NOTAM restricting another seven large chunks of airspace off the PRC coast for periods spanning three days. The map below, created by Duan Dang, displays (in gray and purple) the seven reserved areas outlined in the November 2024 NOTAMS, with the gray zones overlapping with some of the reserved airspaces declared during the December 2024 military exercises (marked in gray and red).
Image: A map displaying the areas of reserved airspace declared by the Shanghai air traffic control in November and December 2024. (Image source: Duan Dang)
The PRC did not provide any reason for the aviation restrictions—which again skirted civil aviation routes—and these measures passed relatively unnoticed by international media. It is possible that they served as a kind of rehearsal for the more provocative airspace reservations that would coincide with the December 2024 military exercises. The PRC may also have been exploring methods to deny entry to United States and allied military aircraft—such as a United States Air Force Boeing RC-135V reconnaissance plane that flew across many areas earmarked in the November 2024 NOTAM in a publicized January 2025 sortie (see image below). By such measures, the PRC may be exploring methods to deny access to adversaries’ air assets.
Image: A map showing the January 9 flightpath of a Boeing RC-135V reconnaissance plane through the Shanghai flight information region (Source: FlightRadar24)
A Slice of the Salami
Based on currently available information, it is not possible to make definitive conclusions regarding the PRC’s strategy in declaring restrictions on the use of airspace along its coast. However, one must examine this activity within the context of the PRC’s long-held strategy of grey zone warfare around Taiwan and its surrounding seas—a policy called “salami-slicing” or “coercive gradualism” (強制漸進主義). Under this strategy, the PRC flouts norms on a piece-by-piece basis, such that it can deny that it is attempting wholescale revisions to accepted international behavior—while, in the long-term, adjusting other states’ expectations about what foreign policy the PRC can get away with. Therefore, when probing into whether a PRC tactic qualifies as grey zone warfare, one must ask: “What norm is the PRC seeking to adjust?”
The November and December 2024 airspace restrictions may be an attempt by the PRC to flex a form of de jure control over the flight information regions (FIR) administered by its air traffic control. As stated above, an FIR is not synonymous with sovereign airspace, which extends only to territorial waters (12 nautical miles from a country’s coastline). If an FIR were synonymous with sovereign airspace, the United States could lay claim to half the airspace over the Pacific Ocean. However, the FIRs over which PRC air traffic control has responsibility hug the Chinese coast, extending beyond the PRC’s territorial waters but not so bountifully as to resemble the sprawling US-administered FIRs. It is possible that the PRC intends to secure tacit recognition that the FIRs it administers are synonymous with its sovereign airspace.
Image: A map showing the flight information regions (FIRs) of East Asia. Delineations of FIRs are marked in blue, while delineations of sovereign airspace are marked in purple. The FIRs titled Sanya, Hong Kong, Shanghai, and Shenyang are the only PRC-administered FIRs intersecting with international airspace. (Image source: ICAO)
The restricted airspace areas declared by the PRC in November and December 2024 crossed beyond its sovereign airspace, but were confined to the borders of the Shanghai flight information region. When a NOTAM has been issued that restricts aviation activity within given coordinates, it is the responsibility of the FIR’s air traffic control authority to selectively grant access to aircraft wishing to enter the restricted area. According to the regulations of the International Civil Aviation Organization (ICAO), military aircraft do not have to heed civil requirements in international airspace. However, it is not inconceivable that the PRC would seek to obstruct a foreign military aircraft’s entry into an area under restrictions by its air traffic control, or that foreign military aircraft would voluntarily comply with these aviation restrictions. Indeed, data from FlightRadar24—a flight tracking platform—reveals that no United States or partner military aircraft with a transponder switched on entered the November or December 2024 restricted airspaces. (It is nevertheless possible that aircraft belonging to the United States or its partners entered the restricted airspaces with transponders that were offline.)
United States Policy
The United States military should be careful not to tacitly defer to a norm under which the PRC could dictate access for any aircraft to the FIRs under its administration. Passive adherence to these airspace restrictions could embolden Beijing into the belief it can interdict future ingress into PRC-administered FIRs, or that it is justified in retaliating through alternative means against military incursions it considers unauthorized. The United States will likely not be the first target for this gray zone “salami slicing.” Rather, it is likely that the PRC would first target a weaker ally such as Japan and test its resolve.
If China imposes another unexplained restriction of international airspace within PRC-administered FIRs, the United States should dispatch aircraft through these areas to demonstrate that the PRC has no jurisdiction beyond its sovereign airspace. The US military aircraft should fly into the reserved airspaces with its transponders switched on so that international media can observe the aircraft’s navigation. In this way, Washington can prevent another possible slice of the salami and stymie Beijing’s attempts to preemptively establish air superiority around Taiwan during a contingency.
The main point: The PRC announced sweeping airspace reservations before and during its unnamed December 2024 military exercises. Beijing did not articulate a reason for these reservations, but the fact they were positioned in between civil aviation routes suggests that they were aimed at denying access to United States and partner military aircraft along the First Island Chain. This operation may have been a feature of the PRC’s gray zone activities that seek to alter accepted international norms. In this case, Beijing may be attempting to establish de jure control over international airspace in the flight information regions (FIRs) it administers. The United States and partners should reject this norm-altering behavior and dispatch military aircraft through a future restricted aviation zone.