Cellphones and airplanes: Why we should hang up

[Troberg]

Originally Posted by erwins

Those are different arguments from the one I was criticizing. Saying there's a back-up for critical systems is different from saying "that it hasn't happened yet is proof that it won't ever happen."

You are thinking backwards. It's the pilot who is the main system. The instruments are his backup.

[WildaBeast]

Originally Posted by jimmy101_again

As to the possibility of a cell phone (or laptop or...) interfering with the avionics... it could be argued that that is the avionics manufacturer's problem. The avionics must be tolerant of signals that are within FCC specifications. Since these devices are within FCC specs it wouldn't be the cell phone users fault, it would the avionics manufacturer.

And under normal circumstances it shouldn't be a problem, but what happens when someone has a malfunctioning cell phone that's producing a signal that's out of spec and is on a plane with damaged shielding on the avionics?

[GenYus234]

Originally Posted by Troberg

You are thinking backwards. It's the pilot who is the main system. The instruments are his backup.

The instruments are his tools. Except for the more advanced autopilots, the instruments are little good without a pilot (or co-pilot).

[AnglRdr]

Originally Posted by erwins

Those are different arguments from the one I was criticizing. Saying there's a back-up for critical systems is different from saying "that it hasn't happened yet is proof that it won't ever happen."

But at some point, "it may happen" should not be conflated with "it is vaguely possible that it could happen."

Given that there are something like 90,000 flights per day, we're getting into the "vaguely possible, but apparently unlikely" territory.

[jimmy101_again]

Originally Posted by WildaBeast

And under normal circumstances it shouldn't be a problem, but what happens when someone has a malfunctioning cell phone that's producing a signal that's out of spec and is on a plane with damaged shielding on the avionics?

The same thing that would happen without the cell phone if the plane was in the vicinity of any high powered ground RF source that wasn't working correctly. Or, more likely, in the vicinity of a high powered ground RF source that isn't malfunctioning. The avionics are going to get confused by a lot of things if there is a shielding problem. Cell phones would be the least of the problems given the number of ~50 kilowatt RF and ~1 megawatt radar transmitters there are.

Since modern electronics are ubiquitous it is clearly up to the aircraft manufacturers to ensure they don't interfere with the aircraft. Heck, a cell phone in checked baggage is likely to be on. Or a laptop in sleep mode that wakes up to do a backup.

Or a solar flare.

RF sources are all over the place. It seems to me that trying to keep low power RF sources out of the aircraft is futile given the much stronger RF signals the plane encounters from itself (its own radar and radios and computers) and from the ground.

[UrbanLegends101]

See PDF page 18, document page 10 at:

http://www.narcap.org/articles/rp1374.pdf

This report mentioned three radio frequency interference (RFI) situations where high power ground based broadcast facilities may have been involved with interference to aircraft systems.

In the case of the North Carolina blimp incident, the blimp passed very near the Site A transmitting station near Beargrass, NC, when the engines quit.

Up through the mid-1980s or so, the VOA transmitter sites at Greenville were used as RFI test locations for several of the Detroit based car manufacturers. New system design vehicles were driven around in the antenna system areas to see if there were any intereference problems.

Generally, however, the field strength level of a cell phone located in the aircraft is probably higher than the field strength of a high power transmitter located several miles away. Remember, generally the closest a flying aircraft is to a broadcast system is when it is directly overhead the antenna system, and broadcast antenna systems aren't designed to radiate a signal straight up.

With that said, however, some RFI situations are almost unexplained. Far too many years ago, probably 1970 or so, I worked with a daytime AM radio station in Georgia which was experiencing RFI into one of the turntables. In the early morning hours, one of the turntables was picking up a series of news broadcasts, one newscast after another, but it wasn't steady and tended to fade much like shortwave broadcasting. Ironically, the turntable system was not affected by the 1 kW transmitter in the next room, which was radiating via the tower about 50 feet behind the station.

Years later, I finally figured out the news programming broadcast was one of the Armed Forces Radio and Television Service (AFRTS) feeder transmissions from a VOA shortwave transmitter at Bethany, OH. I ruled out Greenville, NC being the source, as at the time of day, Bethany was using a SE aimed antenna system, while Greenville was using a NE aimed antenna system.

[snopes]

The ban on electronic devices rests on anecdotes, not on hard evidence — because there isn't any.

http://online.wsj.com/article/SB1000...253402734.html