BANGKOK (AFP) - 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 (7,000m) 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 Mr 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.
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 0.5km in the case of a commercial airliner, and must
not be too far from a cell tower, according to Dr 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 Dr Dewdney, who conducted
experiments after the 9/11 attacks to test the capability of mobile
telephones to make calls from the air.
Malaysia Airline chief executive Ahmad Jauhari Yahya said on Monday
there was no evidence of any attempt by the people on board to make
calls, but he added that "millions of records" needed to be
processed.
"It's being done as part of the investigation," he said, without
elaborating on the type of records being checked.
Deepening the mystery, Chinese media have reported that relatives
heard ringing tones when trying to call passengers' mobile
phones.
But experts believe this does not necessarily mean the phones were
still functioning.
Even if nobody on board the plane tried to make a call, logs of the
"handshakes" might provide some clues about the route taken by the
jet after it disappeared.
While many phones would have been switched off in line with airline
rules, some people may have forgotten to deactivate their
devices.
But to trace any "handshakes" investigators face the challenge of
collecting the unique identity numbers for the passengers' mobile
devices, as well as signal data from network operators in countries
along the possible flight paths, such as Myanmar which still has
limited network coverage.
As the flight turned back and crossed over Malaysia after
disappearing from radar en route to Beijing, it probably passed
over a network area.
After that, the chances of any "handshakes" depend on how low and
close to mobile towers the plane flew.
"Police track cellphones all the time by the last phone call they
made," said Ken Dulaney, a US-based analyst with technology
research firm Gartner.
But he added that this was only possible if the devices were in
reach of a network.
"If they are not in coverage then no one can do anything," he
said.
ST
