Why didn’t missing jet passengers use their cellphones?

March 19, 2014 7:21 am
People take part in support rally for passengers onboard missing Malaysia Airlines (MAS) flight MH370, at a mall in Kuala Lumpur on March 18, 2013/AFP
People take part in support rally for passengers onboard missing Malaysia Airlines (MAS) flight MH370, at a mall in Kuala Lumpur on March 18, 2013/AFP

, BANGKOK, Mar 19 – In the age of smartphones and social media, one question surrounding the disappearance of the Malaysian airliner is why none of the passengers tried to contact relatives, as they did during the 9/11 attacks.

Even the absence of phone calls or emails from those on board the Malaysia Airlines Boeing 777 could provide clues for investigators struggling to solve one of the greatest mysteries of modern aviation.

It may indicate that the plane was flying too high or was over water, or that the passengers were unconscious, possibly due to a change in cabin pressure.

Experts say the chances of the 239 people on board Flight 370 being able to use their mobile devices would have been better the closer they were to a mobile network on the ground.

Many are sceptical that the passengers or crew would have been able to establish and maintain a call using cellphones while travelling at speed, particularly at cruising altitude.

For mobile phones to be used, there must be a contact between the handset and the network — known as a “handshake”. This requires a strong enough signal from both a transmission tower and the phone.

“Theoretically, 23,000 feet (7,000 metres) and 45,000 feet are a cell range that terrestrial mobile network could work with,” said Singapore-based telecommunications consultant Koh Chee Koon, referring to unconfirmed reports of changes in the plane’s altitude after it lost radar contact.

But given the limited transmission power of a commercial mobile phone, as well as the barrier presented by the plane body, “for the mobile phone to connect to the mobile network with acceptable strength and quality would require some luck”, added Koh.

Experts note that in the case of the September 11, 2001 attacks in the United States, the planes were flying at relatively low altitude over areas with cellphone coverage. READ Last words from missing Malaysian jet spoken by co-pilot

In any case most of the calls are believed to have been made from seatback phones and not mobile devices.

Recently some airlines have introduced technology to enable passengers to use their phones in the air using a small cellular base station on board, but Malaysia Airlines said this service was not available on Flight 370.

Without this, a cellphone cannot be used at an altitude of more than roughly 0.5 kilometres in the case of a commercial airliner, and must not be too far from a cell tower, according to A.K. Dewdney, professor emeritus of computer science at the University of Western Ontario in Canada.

“No cellphone could possibly succeed from an airliner in mid-ocean, even if flying low over the water,” he said.

“At normal cruising altitude no cellphone could possibly succeed in making ground contact as it is completely out of reach of the network of towers, in any case,” added Dewdney, who conducted experiments after the 9/11 attacks to test the capability of mobile telephones to make calls from the air.

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