Mythbusters Episode and FMS

On Feb 10, 10:19 pm, **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)
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
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.

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.

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
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
"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
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.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P- Hide quoted text -

- Show quoted text -

Not gonna happen. Avionics have to survive HIRF RF at 100V/M over the
entire RF spectrum.

The real threat is to radio receivers for navigations and
communications. A cell phone can swamp out the receiver and block
important signals. They cannot cause any permanent damage such as you
are describing because of the shielding and other design practices
that are put into place to handle HIRF...

Dean Wilkinson
B.S.E.E. and avionics designer

wrote:

On Feb 10, 10:19 pm, **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)
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
box and a call came in. Whenever I read about A/C having "uncommanded"
control movement, I have to wonder about that environment.





snip

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P- Hide quoted text -

- Show quoted text -



Not gonna happen. Avionics have to survive HIRF RF at 100V/M over the
entire RF spectrum.

The real threat is to radio receivers for navigations and
communications. A cell phone can swamp out the receiver and block
important signals. They cannot cause any permanent damage such as you
are describing because of the shielding and other design practices
that are put into place to handle HIRF...

Dean Wilkinson
B.S.E.E. and avionics designer



Do the levels of the HIRF specs pertain to permanent damage or do they
pertain to "upsets"? I wasn't talking about permanent effects. What I
have seen is that these phones very easily cause upsets to consumer
grade equipment. Granted one would expect avionics to be well sheilded.
I would hope that extends to sensors as well.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P

On Feb 12, 8:51 pm, **THE-RFI-EMI-GUY** wrote:
wrote:
On Feb 10, 10:19 pm, **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)
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
box and a call came in. Whenever I read about A/C having "uncommanded"
control movement, I have to wonder about that environment.

snip

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P- Hide quoted text -

- Show quoted text -

Not gonna happen. Avionics have to survive HIRF RF at 100V/M over the
entire RF spectrum.

The real threat is to radio receivers for navigations and
communications. A cell phone can swamp out the receiver and block
important signals. They cannot cause any permanent damage such as you
are describing because of the shielding and other design practices
that are put into place to handle HIRF...

Dean Wilkinson
B.S.E.E. and avionics designer

Do the levels of the HIRF specs pertain to permanent damage or do they
pertain to "upsets"? I wasn't talking about permanent effects. What I
have seen is that these phones very easily cause upsets to consumer
grade equipment. Granted one would expect avionics to be well sheilded.
I would hope that extends to sensors as well.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P- Hide quoted text -

- Show quoted text -


Avionics aren't supposed to be upset or damaged by HIRF. For some
categories, test levels can be as high as 200V/M

Consumer grade equipment isn't designed to these standards because
they don't need to be, and they can't be due to cost constraints.
Avionics designs are low volume high cost products...

I have designed for both Laser Printers and avionics, and they have
very different design requirements.

Dean