A rare flyover of Taiwan by a United States military transport jet this week raised concerns it was the beginning of more frequent US flights to help the self-ruled island counter growing military threats from mainland China. While mainland analysts said the move appeared to be a test of Beijing’s reaction, Taiwan observers noted that in the past year the US had made the passage of its warships and warplanes in the Taiwan Strait public – switching on signals that could be detected – whenever Beijing staged war games nearby to try to intimidate the self-ruled island. The emission of signals was intended to make the US military presence known to both Beijing and Taipei, an alert that it was deliberately sailing over the Taiwan Strait even though Beijing considered Taiwan its wayward province, observers said. Chieh Chung, a senior researcher of national security study at the National Policy Foundation, an opposition Kuomintang think tank, said that in addition to social media posts about its military activities, the US had allowed its warplanes and warships in and near the strait to be spotted by military watchers and websites such as Aircraft Spots via transponder systems on board. “This way, in addition to warning Beijing, it also means to tell other countries that it has increased its military presence in the region,” Chieh said. “With its presence, the US also means to consolidate its military alliance with South Korea, Japan, Taiwan and other countries and seek their support in countering Beijing over important regional issues.” In a rare flight into Taiwan over the southwest coast on Tuesday, a US Navy C-40A Clipper flew over Keelung, New Taipei, Taipei, Taoyuan, Hsinchu, Miaoli, Taichung, Changhua, and Chiayi before leaving over Tainan and heading towards the open sea, according to AirNav RadarBox. Chinese warplanes enter Taiwan Strait after US flyover With its transponder code on all the way through the flight the US Navy plane, which took off from a US airbase in Okinawa, was last spotted flying towards Taiwan’s Dongsha Islands (also known as Pratas Islands) in the northern part of the South China Sea before landing in Thailand, according to AirNav and other aviation spotting websites. As the US military rarely flies directly over Taiwan, the passage of the C-40A – a Navy version of the Boeing 737-700 and designed to carry high priority passengers such as senior US congressmen and women and officials as well as important supplies – has drawn concern from academics on both sides of the Taiwan Strait. “By flying the transport plane into Taiwan, the US meant to test the reaction of mainland China,” said Zhu Songling, a professor at the Institute of Taiwan Studies at Beijing Union University. He said such tests included highlighting US arms sales to the island, sending warships through the Taiwan Strait and flying warplanes near Taiwan. Local news reports said the US jet had briefly stopped at Taiwan’s Ching Chuan Kang Air Base in central Taiwan but the island’s defence ministry dismissed the claim as baseless. On Tuesday the ministry said the US plane, which had Taiwan’s permission to fly over the island, did not stop at any place on Taiwan. The ministry did not explain why the US Navy jet flew past Taiwan, nor did it say whether it had carried dignitaries. How would China attack Taiwan? A video outlines one scenario Chen Xinxin, a research fellow at the Chinese Academy of Social Sciences Law Institute, said if the US plane did stop at an airport in Taiwan it would be a serious challenge to Beijing. “It could also be a US test of China’s reaction to such a landing, which would be tantamount to recognition of the island’s sovereignty,” he noted. Alexander Huang Chieh-cheng, a professor of strategic studies and international relations at Tamkang University in Taipei, said it was not the first time US military planes had flown over Taiwan but such flights were rarely confirmed or made public by the island’s authorities. “There are two different angles to look at this,” Huang said. He said the non-sensitive angle was that the Navy jet might have needed to take a regular International Civil Aviation Organisation route to its destination, explaining why it had the transponder on to allow air controllers to pick up signals for its flight path. “A more sensitive angle to look at this is the Navy pilot was making a familiarisation flight of the Taiwan path,” Huang said, adding this was important for future flights in times of emergency. Huang said politically motivated or not, the passage represented the deepening of mutual trust between the US and Taiwan. “If there is no mutual trust or understanding between the two sides, no country would allow a military plane to fly into its territory as this is a highly sensitive act,” he said. Huang said it remained to be seen if the US increased the frequency of such flights over Taiwan, or even “normalising” such flights. “This is something worth watching, especially whether it would trigger alarm from Beijing,” he said.