A US Air Force (USAF) plane changed its aircraft identification code as it flew over the Yellow Sea on Tuesday – making it appear like a Philippine aircraft, according to the Beijing-based South China Sea Strategic Situation Probing Initiative (SCSPI).
Aircraft movement monitoring agency Aircraft Spots made a similar observation on Twitter, saying the plane responded with a different hex code when over the Yellow Sea between the Chinese coast and the Korean peninsula.
Hex codes are assigned by the International Civil Aviation Organisation to all aircraft as a means of identifying them.
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When it was over the Yellow Sea, the RC-135S reconnaissance aircraft used a hex code allocated to a Philippine aircraft, but reverted back to its original number after completing its mission, the SCSPI said.
Last week the SCSPI said American RC-135s electronically disguised themselves as Malaysian civilian aircraft while flying close to Chinese airspace. The switch was also reported by Popular Mechanics magazine and several independent observers.
China’s foreign ministry said earlier the US military had used the same trick more than 100 times this year.
Analysts said the incident suggested America was stepping up its surveillance of China and its tactics could stoke tensions between the two sides.
Kenneth Wilsbach, head of the USAF’s Pacific Air Forces, said the aircraft had followed international rules regarding transponders.
“I know we follow the rules for international airspace and we were following the rules that day,” he said.
Ni Lexiong, a Shanghai-based military commentator, said the US reconnaissance missions could target the People’s Liberation Army’s sensitive electronic activities, such as communication and radar signals.
“If a USAF spy plane is spotted within range, such activities [by the PLA] will be silenced,” he said. “But if it appears to be a civilian plane, they might go on as normal and be recorded and analysed.”
Beijing said flying in disguise put civilian aircraft at risk. In 1983, the Soviet Air Force shot down a Korean Airlines KLA007 passenger flight in its airspace, killing all 269 on board, after misidentifying it as an intruding US spy plane.
Ei Sun Oh, principal adviser at Malaysia’s Pacific Research Centre, said given the fact there were not too many civilian planes in the air at the moment because of the Covid-19 pandemic, the US – if it did try to disguise its activities – must have taken a calculated gamble.
Collin Koh, a research fellow at the S Rajaratnam School of International Studies in Singapore, said that even with the growing military tension between China and the United States, in peacetime, a country would not use its air defences against an aircraft until its identity had been clearly confirmed.
“There are clear restrictions on the type of action air defences can take against suspicious aerial activity,” he said.
“The layers of procedures to ascertain the identity of the aircraft, to the set of measures that can be taken, especially in a non-war situation, can be pretty restrictive.”
Ni said that although the US spy planes were an annoyance for China they always stayed outside its territorial airspace of 12 nautical miles.
“So technically they are in international airspace and the PLA can’t actually shoot them down or do too much,” he said.
“But the PLA has been keeping count, which means they can see through the disguise.”
More from South China Morning Post:
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- Sharp increase in US surveillance of South China Sea observed in July
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