Malaysia may have failed to track the missing passenger plane because of human error or an antiquated radar system, according to two Chinese experts.
Li Jiaxiang, administrator of the Civil Aviation Administration of China, said human error might have added to the difficulties encountered finding Malaysia Airlines flight MH 370.
Malaysian personnel might not have detected the signal of the plane when it disappeared on Saturday, Li said.
Professor Yang Minglei, research fellow at the National Laboratory of Radar Signal Processing of China in Xian, Shaanxi province, said Malaysia might not have had a sufficiently advanced radar system to determine whether a dot on a radar screen was the missing Boeing 777.
Li said his office was aware that Malaysian authorities had denied media reports the missing jet was detected by military radar flying off course for an hour at a low altitude over the Strait of Malacca.
"Many mysteries about the plane remain, defying common sense," Li said, adding that the plane had "not been detected by radar completely".
"It is difficult to say why. Maybe the personnel on duty at night shift did not capture the signals in time."
The missing plane was equipped with three emergency radio devices, designed to emit signals showing the plane's location in case of an accident.
Malaysian radar tracks all outbound flights. Two senior Malaysian military officials said they had reviewed military radar recordings and noticed that a weak signal had been picked up from an unidentified airborne object heading west toward the Malacca Strait.
That contradicted the comments of Rodzali Daud, Malaysia's air force chief, who on Wednesday denied that radar detected the plane flying west over the strait.
The military radar systems used by some countries, such as the United States, could detect signals more than 370 kilometres away and gather data about a flying object, Yang Minglei said.
Data, including the size and shape of a flying object and any change in its radio wave's frequency relative to an observer, known as the Doppler effect, could be used to identify an aircraft's type, even if all transponders on the plane were not working, Yang said.
"I don't know exactly what the alert radar system used by the Malaysian military is, but I don't think it would be advanced enough to provide the high-definition data for aircraft identification," he said.
"The conflicting reports might result from a debate about whether a 'dot' was the missing airplane. If their radar can provide no information other than a 'dot', it will be extremely difficult to tell what it is exactly."
Using their best high-definition radar, Malaysian airline officials may have picked up the plane.
"Their air alert system might only see a dot," Yang said.