>> Network, and Discovery Channel) showed at least two passengers who used
>> their cell phones at various times: Tom Burnett and Mark Bingham.
>I don't believe it.
>This is the continued making of another pernicious urban legend IMNSHO.
>popular account of these events ALWAYS cites 'cell phones'. Balderdash.
Well, I do believe it. I work as the System Performance Engineer for one of
the top five wireless carriers in the US.
I have heard anecdotal evidence of cell phone use in General Aviation
aircraft for over 15 years. I know a couple of General Aviation pilots who
have admitted (off the record) use of cell phones in aircraft. I have seen
fellow passengers on commercial aircraft crouched in their seats using cell
phones for years.
The FCC cellular aviation rules were initially placed to protect the
cellular systems (not the aircraft.) An airplane flying at 5000 feet over a
metropolitan area could attempt access up to 50 cell sites at the same time,
and create massive interference to the cellular system.
That same aircraft over the middle of Nebraska, might access only one or two
sites, the cellular network can handle that. (And probably does on a
regular basis.) I have seen 2 hour call records from mobiles traveling
between cell sites located 300 to 500 miles apart. My car doesn't do those
speeds and even if it did, the Nebraska State Patrol takes a dim view of
The FAA rules were put in place to protect from a perceived risk of
interference to aviation systems. I'm not a pilot so I can't speak to that
risk. I would note the closer the phone is to the cell site, the lower
power the phone and the site uses, so there is less interference potential
at low altitudes than high altitudes.
The FAA proposed systems would actually put a cellular system on the
aircraft to keep phone power and interference low (probably in the nanowatt
area.) As a frequent traveler I am against permitting voice usage on
aircraft... (even though I work for a cellular carrier.) I would like to
see data usage permitted.
There are some distance and timing issues involved. They are more critical
with analog, GSM, or TDMA systems than with CDMA systems. Most CDMA systems
can do multiple soft handoffs with up to 6 sectors from up to 3 cell sites.
The CDMA timing constraints are typically stretched enough in rural areas to
permit operation up to 10,000 feet, 35 to 50 miles from the site, at
commercial aircraft speeds.
As a System Performance Engineer I would discourage use of cell phones in
aircraft in normal circumstances. (FCC rules permit a lot broader usage of
radio frequencies in a Emergency.)
So, over rural Pennsylvania, at lower altitudes, it does not surprise me
some passengers were able to use their cell phones.
Darrel Swenson, K0AWB
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