The crashed Malaysia Airlines flight gave one last unexplained signal eight minutes after its final "ping", possibly the result of the plane entering its "catastrophic phase" as it plunged into the Indian Ocean, investigators said.
As families of its 239 passengers demanded "proof" of the plane's demise, Malaysian authorities presented analysis by Britain's Inmarsat, the telecommunications company, of satellite data to explain its conclusion that the plane crashed into remote waters 18 days ago and left no survivors.
No confirmed wreckage from the plane has been found during a multinational air and sea search in waters about 2400 kilometres south-west of Perth, Western Australia.
The search was temporarily called off yesterday due to adverse weather.
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In unprecedented scenes, up to 100 angry relations of flight MH370's Chinese passengers descended on the Malaysian embassy in Beijing, hurling water bottles and chanting for two hours until a diplomat emerged to accept a letter of protest at the lack of information.
The Chinese government called for Malaysia to release all the satellite data it used to conclude that the plane was lost. Xi Jinping, the Chinese president, said he would send a special envoy to Kuala Lumpur.
Adding another puzzle to the list of questions over the flight, which flew on for seven hours after it vanished from radar, Malaysian authorities said that the plane appeared to make a final satellite contact after the last of its routine electronic "handshakes" was emitted.
That series of seven routine hourly "pings" had been used to pinpoint what is thought to be the plane's final location over the Indian Ocean.
Relatives of passengers onboard flight MH370 march toward the Malaysian embassy in Beijing. Photo / AP
"There is evidence of a partial handshake between the aircraft and ground station at 00:19 GMT," said Hishammuddin Hussein, the acting transport minister. "This transmission is not understood and is subject to further ongoing work."
Thomas Withington, a defence electronics analyst, told The Daily Telegraph: "It sounds like the aircraft began to squawk a message and for some reason this was curtailed. It could be because the aircraft was at a catastrophic phase of its flight - that something was causing it to crash - or there could be some atmospheric disturbance.
"Was a crew member trying to send a message? Was the aircraft trying to send a message? Was there a malfunction? Those questions can only be answered if the cockpit voice recorders and flight data recorder are recovered."
Authorities have used the new analysis to narrow the search zone from an area of 2.4 million nautical square miles to one of 469,407 nautical square miles - albeit still twice the area of France.
Watch: MH370: Family members grieve
Anger in Beijing at the Malaysian authorities boiled over yesterday morning, 12 hours after relations were sent text messages to tell them the passengers were believed to have all perished.
Having been kept waiting almost an hour for a promised meeting with the Malaysian ambassador, they streamed out of their hotel, carrying placards and wearing T-shirts with the slogan "Save MH370".
Four public buses were waiting, with police inside, to ferry them to the embassy for what appeared to be an organised protest. But, after waiting 20 minutes for the buses to depart, the relations lost patience and decided to walk.
As Chinese police shut down some of Beijing's busiest roads and diverted traffic, the group marched for 2.4km in silence, before bursting into angry shouts outside the embassy gates.
"They have no respect for us, no respect at all," said Steve Wang, one of the relations. "They promised a full briefing at 10am but they did not come. We want the truth."
In Kuala Lumpur, Malaysia Airlines defended its decision to inform families of the deaths by text messages, saying it had done so only after trying to contact them in person or by telephone.
At a press conference overlooking the airfield at Kuala Lumpur airport from where MH370 took off, Ahmad Jauhari Yahya, the airline's chief, said family members had been offered 24-hour counselling and $5,000 each.