Beijing has accused the US of disguising the identities of its warplanes as civilian aircraft to spy on China at least 100 times this year, describing it as a “serious security threat”. “It’s a common trick for the US Air Force to impersonate the transponder code of civilian aircraft from other countries … It is of a vile nature,” Chinese foreign ministry spokesman Wang Wenbin said earlier this week. “We urge the US to immediately stop such dangerous provocations, to avoid accidents from happening in the sea and air.” Wang described Chinese records of American spy plane activity in the area as “incomplete”. His remarks appeared to confirm a report by Beijing think tank the South China Sea Strategic Situation Probing Initiative (SCSPI) which it said showed US planes were electronically disguising themselves as civilian aircraft from Malaysia while flying over the disputed waterway. Malaysia has not confirmed or responded to the claim. According to the SCSPI, which monitors activity in the South China Sea , between September 8-10 US spy planes disguised as Malaysian aircraft flew over the disputed Paracel Islands as well as the sensitive Taiwan Strait and the Yellow Sea near the Chinese coast, basing its conclusions on open source aviation responder records. “This undoubtedly added up to great risk and uncertainty to international flight safety, which could lead to misjudgment (by ground air defence systems) and probably bring danger to civilian aircraft especially those being impersonated,” the think tank said in its report. All planes registered with the International Civil Aviation Organisation (ICAO) are assigned a unique 6-digit code called a “hex code” which rarely changes. The code is transmitted by an aircraft’s transponder when interrogated by air traffic control radar. If the device is turned off or reconfigurated, there is a danger of misidentification and even a mid-air collision. US spy planes in South China Sea ‘creating risk’ for civilian aircraft One of the best known incidents of misidentification occurred in 1983 when Korean Airlines flight 007 was shot down by the Soviet Union air force, killing all 269 on-board. The civilian plane was mistaken for a US spy plane after an RC-135 was observed crossing its flight path in Soviet airspace. Last month a source told the South China Morning Post that a US E-8C spy plane had initially been identified as a commercial airliner until it flew near the province of Guangdong on the southern Chinese coast. The US Air Force, which has stepped up its activities in the South China Sea in recent months, uses commercial aircraft platforms for several of its plane – the RC-135 is based on a Boeing 707 – which allows them to take civilian cover. The SCSPI report said over three straight days in September it recorded the “disappearance” of reconnaissance planes soon after they left US airbases in Okinawa and Guam. Later, at the same heights and flight paths, aircraft with codes identifying them as Malaysian flew in “suspicious” patterns or to destinations not usually associated with civilian routes, it said. As additional evidence for its conclusion, the report said a US Air Force tanker aircraft had left the Anderson airbase in Guam for the South China Sea on September 10, at the same time as one of the reconnaissance planes, suggesting aerial refuelling. In late August SCSPI also used open source aircraft identification information to claim a US EP-3E reconnaissance aircraft may have landed in Taiwan. This was later denied by Taiwanese authorities as “totally against the facts”. SCSPI said the US Air Force had a track record of changing transponder numbers on its aircraft to those of civilian planes for undercover reconnaissance in places like Iran or Venezuela. Are China-US relations drifting closer towards war? Hong Kong-based military commentator Song Zhongping said a US spy plane with a fake identity could reach military or civilian targets within Chinese airspace, getting as close as possible to the coastline without attracting the attention of PLA air defences. “They pretended to be Malaysian because that is a South China Sea nation and has relatively good relations with China, so it would be less likely to raise a flag,” he said. Song said disguising warplanes as civilian aircraft not only violated the Convention on International Civil Aviation, but also the China-US code of safe conduct on naval and air force encounters, signed in 2014. “This shows how much the US armed forces are keen to know the PLA’s deployment and are preparing for potential military actions,” he said. Earlier last month, a US surveillance plane flew into a declared no-fly zone over a Chinese military exercise in the Yellow Sea, prompting a protest from China’s defence ministry.