Philippines Accuses China of Jamming AIS and Communications in South China Sea

Joaquin Camarena
Joaquin Camarena
Joaquin completed his undergraduate and graduate education at a Texas university and has studied extensively in China. As a former Marine Corps intelligence analyst, he worked in the Indo-Pacific region. His areas of expertise include PLA modernization, particularly PLAN/PLANMC and its expeditionary capabilities, as well as CCP and Chinese domestic politics. He also runs the Sino Talk brand on Instagram and Twitter and is the IndoPacific Desk Chief for Atlas.

More From Me

Philippine Navy and Coast Guard Statements

Philippine Navy (PN) spokesperson for the West Philippine Sea, Commodore Roy Trinidad, said its vessels received “electronic interference” (i.e., jamming) during South China Sea (SCS) operations on February 27th. The spokesperson pointed out that the jamming occurred as the Philippines prepared for resupply missions to Second Thomas Shoal and Thitu Island. Trinidad also said in the daily press conference that the jamming did not have any “serious impact” on their land-based communications or navigation systems and that their systems remain secure. The spokesman said that these activities conducted by China in the SCS “have been going on for the past three to four years, maybe even earlier.”

Philippine Navy spokesperson for the West Philippine Sea, Commodore Roy Trinidad during February 27th briefing (Photo: Manila Bulletin/Martin Sadongdong)

During the briefing, Trinidad said that the PN has had several contingencies in place for several years to deal with the interference received during SCS operations. The spokesperson, however, reiterated that the jamming “did not reach a stage” to affect or have any “significant impact” on the PN’s navigation systems. Trinidad did point out that the interference would affect land-based communications, such as radio transmissions and cellphones, if used in the SCS operations. However, the jamming would have little effect, if any, on the ship’s navigation systems as they operated in the SCS due to the safeguards they have in place.

Trinidad’s comments come after Philippine Coast Guard (PCG) spokesperson Commodore Jay Tarriela said that the China Coast Guard (CCG) jammed the Automatic Identification System (AIS) of PCG or Bureau of Fisheries and Aquatic Resources (BFAR) vessels. The spokesperson said that the service noticed that the BRP Teresa Magbanua’s and BRP Datu Tamblot’s AIS were jammed at times during their rotational deployments. Tarriela said that the AIS signal to the two ships was prevented from transmitting their signals on commercial AIS monitoring programs. The spokesperson pointed out that the Philippines assumed that China conducts the jamming “every time they release their statements that they repelled” the vessels.

February 22nd Jamming Incident

Tarriela’s comments were likely validated on February 22nd, when the BRP Datu Sanday’s AIS signal was jammed during its rotational patrol at Shoal. The incident began at 8 a.m. local time when a CCG vessel blocked the Datu Sanday when the vessel delivered fuel and groceries and provided security to Philippine fishermen.

Screenshot of People’s Liberation Army Navy Z-9C during February 22nd incident (Photo: Philippine Coast Guard)

A People’s Liberation Army Navy (PLAN) Z-9C also launched from a CCG vessel and flew around the area. During this time, the Datu Sanday determined that it was unable to transmit its AIS signal due to the signal being blocked. The CCG issued a statement on their website and Chinese social media that they “monitored and repelled” the Datu Sanday when it “illegally intruded into waters adjacent to China’s Huangyan Dao [Scarborough Shoal].” Furthermore, the Global Times posted an English translation of the statement on western social media.

Photo of Philippine news reporters recording and taking pictures from BRP Datu Sanday on February 22nd

While the AIS signal was jammed for approximately one day, several Philippine news reporters were aboard the BFAR vessel and recorded the incident as it occurred. The personnel onboard the BFAR vessel also recorded footage of the incident, including the Z-9C flying around the area. The Global Times also made a post referencing the reporters on February 24th, alleging that they were onboard the Datu Sanday to record “in an attempt to smear and hype the CCG’s operation.”


The statements by both the PN and PCG alleging that China is actively jamming or conducting other forms of Electronic Warfare (EW) are likely true. Furthermore, the country likely conducted EW operations against Philippine vessels for as long as Commodore Trinidad alleged during the February 27th press conference.

China actively jammed or disrupted Philippine AIS signals and communications during their presence patrols to provide ‘evidence’ to support their narrative that they ejected PCG or BFAR vessels from disputed areas. Furthermore, the jamming also assists China in preventing the Philippine or foreign governments from monitoring the vessels during the resupply missions or patrols the country conducts. There is evidence that supports this argument, such as the speed with which the CCG published a statement of their version of the February 22nd incident, about an hour after the event occurred. The CCG likely had a pre-prepared statement that they used to quickly push their narrative to the wider world.

Another piece of evidence was the February 24th Global Times post that described the reporters’ presence on the Datu Sanday as an attempt to disparage the CCG’s operation at the Shoal. China likely learned that the journalists and PCG personnel on the Datu Sanday transmitted the pictures and footage of the incident back to the Philippine mainland. The Global Times made the post in an attempt to paint the journalists in a negative light. The jamming of radios and cellphones is also another piece of evidence pointing to China trying to prevent the Philippines from pushing against the narrative. The journalists, PCG, and BFAR personnel routinely transmit updates or make posts on social media during these patrols to provide real-time evidence that disproves China’s narrative.

It is likely that the PLAN Z-9C jammed the Datu Sanday’s AIS signals during the February 22nd incident. The reason why is due to the helicopter’s launch from a CCG vessel shortly before the incident, which circled the area. The helicopter likely carried jamming equipment that prevented the AIS signal from being transmitted. However, the deployment of the PLAN helicopter to likely jam AIS signals points to a slight escalation regarding China’s actions.

Furthermore, the Z-9C’s deployment also indicates that China will not only continue its use of gray zone tactics but also utilize new methods, such as using PLAN helicopters from CCG vessels. China’s use of PLAN helicopters under CCG command would not violate international law and would allow the CCG to enhance its vessels’ situational awareness and surveillance capabilities. However, the deployment of Z-9Cs onto CCG vessels would also allow the service to access weapons that its own Z-9 helicopters lack.