China's first domestically built aircraft carrier, Type 001A, is heading out for more testing in north of Yellow Sea, with observers saying issues may have been identified that need to be fixed

Take-off and landing tests were conducted during four-day sailing last week

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China's first home-grown aircraft carrier is undergoing another sea trial, straight after four days of testing, suggesting that the PLA Navy may have identified technical problems requiring immediate attention, military observers said.

The latest sea trial of the 65,000-tonne Type 001A was indirectly confirmed by a "no-sail zone" notice issued by the Liaoning Maritime Safety Administration on Monday. Ships have been warned not to enter a 3,400 sq km area in the north of the Yellow Sea for safety reasons.

The "no-sail zone" — near Dalian port, where the warship was built — is almost the same area used for last week's sea trial. A military source said the area was chosen to facilitate operations and emergency support.

Although the previous sea trial was not officially announced, the Type 001A was seen returning to Dalian port on Sunday after completing the testing.

China's Type 001A aircraft carrier. Getty Images

Song Zhongping, a military commentator for Hong Kong-based Phoenix Television, said the back-to-back sea trials indicated there could be technical issues with the warship.

"The fact the aircraft carrier needed to be tested again within two days suggests that the navy may have found some technical problems in last week's sea trial that needed to be fixed immediately," he said. "It's fairly typical before an aircraft carrier is officially commissioned — we can expect to see more intensive sea trials in the future."

Military enthusiasts following the Type 001A's development spotted a J-15 fighter jet and a helicopter on its deck when the vessel was tugged from Dalian port to the Yellow Sea on Thursday.

A Beijing-based military source said takeoff and landing tests were conducted in last week's sea trial, noting that the proximity of the location to port enabled the navy to better manage the testing and provide support in case of emergency.

"Takeoff and landing tests are the most challenging and complicated parts of the sea trials, and that's why the location is not far from the coast, just in case there's an accident," the source said.

He added that more testing would follow because the Type 001A was built to operate as a warship rather than a training platform like the Liaoning, China's first and only operational aircraft carrier.

"China has built more than 50 J-15 fighter jets and trained dozens of aircraft carrier-based pilots, and the squad is big enough now to deploy on both the Liaoning and the Type 001A," the source said.

Chinese J-15 fighters conduct a drill aboard the aircraft carrier Liaoning in the South China Sea. REUTERS/Stringer

The Liaoning started life as a Soviet Kuznetsov-class vessel and was unfinished when China bought it from Ukraine in 1998. It underwent 10 sea trials before it was commissioned in 2012.

China built the Type 001A based on the design of the Liaoning and launched it in April 2017.

In May last year, the defence ministry said the Type 001A had met "initial operating capability" (IOC) requirements. But Beijing-based naval expert Li Jie said that according to his information, the vessel had yet to satisfy all the IOC requirements.

"The Liaoning has sailed on the high seas in several naval drills now, with different carrier battle group formations, but the Type 001A still needs more time before it can meet all the IOC requirements," Li said.

"As well as testing the propulsion system, they also need to make sure the aircraft carrier's electronic communications can connect with all the military radio systems properly," he added.

Song expected the warship to be ready in time to join navy celebrations to mark the 70th anniversary of the founding of the People's Republic of China on October 1. But Li said the aircraft carrier's commissioning would depend on the results of the sea trials.