It's a popular question on social media: Why didn't passengers on board the missing Malaysia Airlines Flight 370 make mobile calls?
Many recall that when
United Flight 93 was hijacked on September 11, 2001,
passengers were able to
make two cell phone calls during the flight's final moments. Several other
calls were made using airphones.
If metadata was
detected from cell phones on Flight 370, surely it would shed more light on the
missing plane's flight path?
The plane may have
been flying too high or too fast to register with cell towers, according to
telecoms experts, but careful analysis of the passengers' cell phone records
will need to be completed to be certain.
"So far, we have
not had any evidence of any telephone company of any member trying to
contact," said Malaysia Airlines CEO Ahmad Jauhari Yahya at a news
conference on Monday.
"But anyway, we
are still checking. There are millions of records to process. It is being done
as part of the investigation."
Was the plane
too high?
According to radar
analysis, the plane is believed to have been flying as
high as 45,000 feet and as low as 23,000 feet.
But even this lower
altitude is too high to register with mobile towers, experts say.
"If you look at
the data in this case, the altitude at which the planes were traveling is too
high," Vincent Lau, wireless communications specialist and professor at
the Hong Kong University of Science and Technology's Department of Electronic
and Computer Engineering, told CNN.
"Even on the
ground it wouldn't be easy to pick up from that distance, and if you are flying
it's even more difficult because at those angles you are only picking up what
we call leakage from the side loops of the antennas, which are substantially
weaker than the signals from the main loops of the base stations."
While business class
seats on the aircraft are known to have been equipped with phones that worked
via satellite, it would be easy to strike down that system from inside the
plane, said Lau.
Reports on Monday
that the plane flew as low as
5,000 feet or less over mountainous terrain -- possibly in order to
evade radar detection -- haven't been confirmed.
"In terms of the
altitude it would have to be no higher than around 10,000 feet. Anything higher
... would be problematic," according to Bill Rojas, director of telecom
research at IDC Asia Pacific.
Unlike in urban
areas, where cell phone antennae are typically pointed down toward the ground,
cell towers in rural areas are up to 30-45 meters high and are often pointed at
an angle meant to cover wider distances.
So if you're up in
the sky, you can receive the signal as well, Rojas said.
"If the airplane
were flying over northern Malaysia or southern Thailand -- basically the rural
area -- then it's very possible that a cell tower could register the signal
from the phones, assuming they were on," said Rojas.
"Technically it
is possible."
Retrieving the data
If smartphones had
been on and registered with a cell tower, the records would be relatively easy
to retrieve.
"The
registrations would typically be logged and depending on the operator they will
be kept for hours, days or months," said Rojas.
The telecom expert
said that he'd place particular focus on the phone numbers of passengers from
Thailand or Malaysia.
"I would assume
that the authorities are checking with the mobile operators by comparing known
passenger cell numbers to see if there were any pings or attempted or
successful network registrations in northern Malaysia or southern Thailand or
possibly even Indonesia," said Rojas. "Any passenger who had roaming
capabilities or a local Malaysian number -- if the plane were over Malaysia --
could in theory have been registered on the network if their phone was on.
"If a passenger
does not have international roaming then their access would be rejected by the
network and for a period of time that metadata might be stored by the
network."
If the metadata
records were erased automatically after a few days or a few hours, could they
be retrieved?
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