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Chinese aviation experts said it will be difficult to locate the missing aircraft due to technical reasons.

The signal sent by the flight data recorder, or commonly known as the black box, will be significantly disturbed by seawater, leading to difficulties to locate the aircraft's whereabouts, according to Wang Ya'nan, deputy editor-in-chief at Aerospace Knowledge magazine,

"Normally, the device is able to transmit its signal within a radius of 10 to 20 kilometers, but seawater blocks the transmission," Wang told China Daily. "After the 2009 crash accident of Air France flight 447, it took investigators nearly two years to find the recorder in the depth of 3,900 meters under the sea because its signal failed to reach the searchers."

A flight data recorder is an electronic device used to record any instructions sent to any electronic systems on an aircraft and records conversation in the cockpit, radio communications between the cockpit crew and others, as well as ambient sounds.

Wang's remarks were echoed by Wu Guanghui, deputy general manager of Commercial Aircraft Corp of China.

"If an aircraft falls at a high speed at its cruise altitude, the whole plane will scatter in the air so the black box could be far from the exact location of the accident," Wu said. "In addition, the device has a limited transmission range, which means it is very difficult to locate it in the vast ocean in a short time."

For a normal flight, the aircraft would be detected and identified by the air traffic control radar beacon system once it enters a nation's territorial airspace, he explained.

"-Even the aircraft encounters some emergencies, its onboard equipment including the black box and radio beacon will sent out signals automatically," Wu said. "The fact that the ground control hasn't received any signal leads to one possibility that it met an extremely serious situation during the flight."

Wang added four technical and meteorological conditions could happen to an aircraft and result in serious accidents.

"The aircraft might scatter up in the air or had some severe malfunctions," he said. "It is also possible, though rare, that the plane was struck by lightning or clear-air turbulence."

Clear-air turbulence is the turbulent movement of air masses in the absence of any visual cues such as clouds and can be hazardous to the safety of aircraft in flight.

The search for the plane will be time-consuming, said Wu Peixin, an aviation expert in Beijing. He explained that such operation usually involve large-scale combing by aircraft and ships without more efficient methods.

"Even the surface search radar used by the navy is designed to detect ships rather than small pieces of scattered plane," he added.

Wang suggested that the Vietnam Coast Guard should dispatch its three CASA C-212 maritime patrol aircraft to search the scour the seas because the plane is capable of scaning the sea surface with its radar and tracking the possible oil trace by optical instruments.