Mythbusters Episode and FMS

On Sun, 11 Feb 2007 00:19:32 -0500, **THE-RFI-EMI-GUY**
wrote:

Its just plain good sense not to use cellphones in an aircraft. Has
anyone noticed how a NEXTEL phone will tear up speaker phones and
computer monitors? Its the pulsing of the time division multiplex (TDMA)

Nope. I have both right here and with no problem.

RF signal that gets inadvertently coupled into electronics and biases
transistors on and off. Think what would happen if a passenger left that
phone turned on in a bag near a bulkhead next to some sensitive avionics

The wiring in an aircrafti s well shielded.

box and a call came in. Whenever I read about A/C having "uncommanded"
control movement, I have to wonder about that environment.

wrote:

On Jan 25, 8:15 am, "Marco Leon" wrote:


Saw a repeat episode of Mythbusters for the first time last night about
the use of cell phones on an airplane and interference with cockpit
instruments. I know that this was mentioned in a November 2006 thread
briefly but the short of it was that they concluded cell phones really
CAN interfere with the VOR signals.

Not really. They determined it can be done when none of the wiring in
the test cockpit is shielded.




Sometime in the last year or two, the IEEE (the main EE professional
society) had an authoritative article about this in their monthly
magazine "IEEE Spectrum." The bottom line as I remember it: 99.999% of
cell phones and other electronic gizmos cause absolutely no
interference to flight instruments. (The 99.999% figure is indicative,
not exact.) But, very rarely a cell phone or other electronic device
gets out of spec on RFI (but still "works" so far as the user is
concerned) and can make the FI's go haywire.

A lap top or probably more likely to cause a problem.


The authors conclude that unrestricted use of cell phones and other
electronic devices (including ones now allowed) will probably cause a
crash something like once every decade or so. I forget the number, but

That was one of those programs where the result was it might , maybe,
we think could possibly... IOW they thought the possibility might
exist but could not say any thing specific. Some day one may get hit
by a meteor too. Who knows?

it's in that ball park -- the kind of thing that, until it happens, the
regs seem overly restrictive. But after it happens, everyone will ask

What regs? Last I knew the FAA had *no* regulations on the use of
cell phones or other electronic radiators in aircraft with one
exception. No intentional radiating devices may be used while the
aircraft is operating by reference to instruments alone and I do not
know if that pertains to commercial flights as well as GA..

The cell phone ban is an FCC regulation which may disappear in the not
too distant future.
Remember as long as it's turned on it's transmitting whether you are
using it or not. Only when turned completely off does it stop
transmitting.
"Why didn't they ban those devices?" If memory serves me, the authors
cannot rule out that such crashes have already happened.

The authors had done a study in which they planted a measuring device
in a suitcase and flew it on a large number of flights in an overhead
bin, and recorded the EM spectrum. Interestingly, they found cell
phones were used illegally about once per flight or thereabouts. They

I find it difficult to believe as every one that was forgotten would
have been transmitting. Many will stop working. I don't know how many
times I've forgotten mine in the Deb but I always have to turn it off
and back on before being able to use it.

also found a number of cases where a device had failed, at least in the
sense that its spectrum could cause interference to GPS and other FI's.
They also reported one incident where an airliner's FI's went haywire
and the captain asked everyone to shut down all electronic devices. The
FI's recovered, and a bit of sleuthing traced the problem to one
passenger's device.
Probably a lap top.
Lap tops and games are particularly bad. Add to that most lap tops now
have built in WiFi.

Generally they aren't a problem and when they have been its been quite
evident.




Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com