Do electronic gadgets threaten airplanes after all?

N. Dan Smith

Tue Apr 11 07:13:29 -0700 2006

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I am curious as to why, of all the radio signals transmitted and received by a plane, cell phones are the only ones which cause harmful interference.

Do electronic gadgets threaten airplanes after all?

Beryllium Sphere(r)

Tue Apr 11 08:57:24 -0700 2006

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Cell phones are the only common passenger-carried devices that transmit more than half a watt. They have more chances to cause problems because they put out a (relatively) high amount of power. It's possible that other passenger-carried devices are causing problems are causing problems and the editorialists just didn't have space to discuss them.

Somebody, we can hope, does electromagnetic compatibility testing on the plane's built-in devices.

Do electronic gadgets threaten airplanes after all?

Technocrat.net Editor

Tue Apr 11 12:01:10 -0700 2006

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There are two GSM telephony bands reasonably close to GPS. Transmissions on them can cause front-end overload on GPS recievers. Your phone will transmit on one or the other depending where you are. They listen first, and don't transmit without hearing a beacon from the cellular base station.

Also, there is the local oscillator and IF issue mentioned elsewhere. Generally a superhetrodyne receiver will transmit at low power whenever it's on, at a whole list of frequencies. These include the frequencies of all intermediate-frequency oscillators, the mixing products of each IF with each other, and the mixing products of the first IF with the frequency you are listening to. Since cell phones scan for beacons, this can be even more frequencies. Mixing products would be F1 + F2, F1 - F2, and then you have harmonics, mixing products of harmonics, etc.

This is one reason we have Part 15 of the FCC rules. It places limits on unintentional radiators.

Make it a feature, not a danger

bill_mcgonigle

Wed Apr 12 12:36:09 -0700 2006

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Cell phones are the only common passenger-carried devices that transmit more than half a watt.

They could just put repeaters on airlines and those cell phones would barely transmit at all (they ramp up power as necessary).

Besides safety, it would be a major selling point for passengers. They could use a dumb repeater or actually pretend to be a cell tower, if they want to handle satellite hand-off for overseas flights.

Do electronic gadgets threaten airplanes after all?

jeblucas

Tue Apr 11 09:03:18 -0700 2006

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My current cell phone certainly wakes up the gremlins in my PC speakers and our baby monitor. When I'm at the computer I know my cell is going to ring about 0.5 sec before it actually does because I get a "Zzzz Bupp bupp bupp" sound from the speakers--then it vibrates. Someone else's phone is freaking out our baby monitor (it's the same "Zzzz bupp bupp bupp" sound, but neither of our phones ring). It's no wonder there's interference, these things are just CHURNED out. Here's a snippet from the FDA's website:

  Radiofrequency energy (RF) from wireless phones can interact with some electronic devices.

Hmm. Where does a guy like me find some electronic devices?

Do electronic gadgets threaten airplanes after all?

AB3A

Tue Apr 11 10:50:32 -0700 2006

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Another common source of interference with aircraft navigation are the local oscillators of broadcast band receivers.  Back in the bad old days when NDB ruled the navigation world, these could be insidious little buggers.  These days, the LF NDB band is about to evaporate in a puff of smoke.  Most pilots I know placard their recievers as inoperative so that they don't have to use them on a checkride.  But just so you know, I had to do a partial panel NDB approach on my instrument checkride.  It was no picnic, though I did pass.  Most pilots I know use NDBs as only a last resort, so interference isn't much of an issue there.

But the worst of the bunch is the FM broadcast band LO.  It's not often that one will radiate, but when it does, it is right on top of the navigation band signals you're trying to use.  This makes VOR or ILS signals very suceptable.  The VOR signal problems aren't that big a deal, provided it isn't being used for an instrument approach.  The ILS signals are another issue entirely.  Those are precision signals used by airliner and private pilot alike.  Airliners are aiming at a window in the sky of only 10 feet high and 20 feet wide.  This window is only 200 feet above the ground and they're screaming toward it at typical speeds of 150 MPH. 

Would you like to listen to your FM radio while the airliner is doing an autopilot coupled approach in 0-0 conditions?  I didn't think so...

 

Do electronic gadgets threaten airplanes after all?

Lindsey

Tue Apr 11 10:55:07 -0700 2006

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I remember when GPS was just starting to become commong for airplane navigation some people were worried what would happen if the US went to war and decided to turn it off for everyone but their own military.  Is that still an issue?  

Do electronic gadgets threaten airplanes after all?

Technocrat.net Editor

Tue Apr 11 11:52:47 -0700 2006

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Yes. This is one reason that the Europeans are building their own GPS. Also, it's a good reason for us to continue to put windows in the cockpit :-)

Do electronic gadgets threaten airplanes after all?

AB3A

Tue Apr 11 12:07:31 -0700 2006

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It's not as much of an issue as the Europeans would like you to believe.  VOR still exists, and let's not forget good old deduced (ded, or dead) reckoning. 

On the other hand, would I build an entire navigation system based exclusively upon GPS?  No.  And nobody is suggesting that anyone fly with just this method for navigation. 

The Europeans have also conveniently neglected Differential signals which can de-fuzz the signal well enough to enable very precise landings.  However, even that is no a major issue.  I think the Magellen system was mostly a matter of pride by the European nations to prove they could do better than GPS.  Given the age of GPS, that's not a difficult feat any more.  It also gives them a government controlled tax revenue (precision from this system is doled out with keys which will be taxed...). 

I wish them well.   If inexpensive receivers become available here in North America, I may seek to add one to my airplane as a backup. 

 

Do electronic gadgets threaten airplanes after all?

Bryan Reece

Tue Apr 11 12:58:45 -0700 2006

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clusively upon GPS?  No.  And nobody is suggesting that anyone fly with just this method for navigation.

Phase out of VOR/DME from the NAS is anticipated about 2005 with completion by 2010.
-- http://www.navcen.uscg.gov/pubs/gps/crd/crd2-28.html


See also http://www.ainonline.com/Issues/03_06/0306_ILSphaseout_65.htm , which mentions both a phaseout of category-I ILS and keeping an ILS at each ILS airport.  I'm not sure whether that means only cat-II and -III airports will keep

Do electronic gadgets threaten airplanes after all?

Lindsey

Tue Apr 11 12:59:06 -0700 2006

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  And nobody is suggesting that anyone fly with just this method for navigation.

I was under the impression that that's exactly where people were going. 

Do electronic gadgets threaten airplanes after all?

AB3A

Tue Apr 11 13:38:13 -0700 2006

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Well, don't expect it to happen overnight.  And by the time VOR technology is phased out we'll have inexpensive inertial navigation to go with the rest of the instrumentation we use in the cockpit.  That, ATC radar, LORAN, Magellan, and GPS will be plenty of redundancy for even the most paranoid person to fly with...

Do electronic gadgets threaten airplanes after all?

Technocrat.net Editor

Tue Apr 11 19:42:04 -0700 2006

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LORAN? It's still around?

Do electronic gadgets threaten airplanes after all?

AB3A

Wed Apr 12 13:37:13 -0700 2006

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Still works too.  I flew in a friend's airplane recently with a completely functional LORAN.  No, it's not as good as GPS, but don't sneer.  It's still better than VOR most of the time.

Technology Review weighs in

Beryllium Sphere(r)

Tue Apr 11 20:13:45 -0700 2006

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They have an article which says fears of RF interference to aircraft systems are overblown. They link to an article by the Av Week editorialists, CMU researchers arguing that cell phones are dangerous.

One quote in the Technology Review article really pushed my buttons.

no airline crash has ever been attributed to radio emissions from devices brought onboard by passengers

People die when engineers start thinking like that around safety-critical systems. Use science and not anecdote to form opinions, prevention and not reaction to guide decisions. Until you can say "we've qualified this block release of the avionics installed in this airframe to stay within these tolerances with this reference power spectrum from the cabin" you have no business risking hundreds of millions of lives a year.

Do electronic gadgets threaten airplanes after all?

mcrbids

Tue Apr 11 11:47:53 -0700 2006

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I fly a fair amount. Typically 1-2 times monthly on commercial flights. I'm also a private pilot, a member of AOPA and am likely to buy my first private plane next week.

I was on a SouthWest flight about 4-6 months ago, in an aisle seat, typical SouthWest Boeing 737. About 4 rows ahead of me was a pilot in uniform, with the gold shoulder epaulettes and everything. As the flight attendant was explaining to everybody about turning off their cell phones and/or laptop computers, the pilot was busy gabbing business with his (very ordinary-looking) cell phone.

He continued to talk thru the takeoff, and stopped AFTER we made it to 10,000 feet. (which is when you usually get an OK to turn on laptop computers)

Combine that with the fact that I've always flown in private planes, complete with most of  the instruments mentioned (VOR/ILS, GPS, transponder, no radio altimeter, though) with my tri-band cell phone turned on, at my hip, and it seems pretty clear to me that the hype around cell phones is just overactive conservatism. I don't blame them - all it takes is one mishap to make the news - but the SouthWest pilot obviously didn't mind sticking his neck out a little.

I know it's anecdotal evidence, but I certainly don't worry much about it.

It's really dumb, though - aviation is safer per hour of travel time than a car (deaths per hour of passenger travel time) but when you consider that planes go from 2 to10 times faster than cars, they are many, many times safer! So incredibly stooooopid  that it's the plane crash that gets all the news coverage, simply because there's so many car crashes nobody even cares anymore...

Do electronic gadgets threaten airplanes after all?

Technocrat.net Editor

Tue Apr 11 11:51:48 -0700 2006

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Said pro pilot can probably tell when the plane is on visual flight rules or instrument flight rules. I tend to take the cell phone stuff much more seriously for an instrument landing.

Do electronic gadgets threaten airplanes after all?

mcrbids

Tue Apr 11 13:03:54 -0700 2006

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Said pro pilot can probably tell when the plane is on visual flight rules or instrument flight rules. I tend to take the cell phone stuff much more seriously for an instrument landing.

But, see, even when I've flown under IFR rules, either "under the hood" in training, or actually in the clouds, I've had the phone at my hip, turned on. I've taken calls while in the air.

Since I'm a system administrator, I'm required to be "on call" as close to 24x7 as is possible. I've never, ever flown without my phone a t my hip, and I've never been asked, even by the flight instructor to turn it off. And, I've certainly not noticed any "weirds" around the instrumentation.

Heck, there are even headsets for private planes that you can buy with a plugin for cell phone calls!

Do electronic gadgets threaten airplanes after all?

AB3A

Tue Apr 11 12:32:45 -0700 2006

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On a recent IFR flight to Tampa Florida, I forgot to turn my cell phone off while flying in instrument conditions.  I'm still here, so clearly it isn't always a problem.  Even on IFR flights, I don't like to make instrument approaches to airports I've never been to before.  I'm generally very conservative about weather.

In cruise a cellphone isn't much of an issue.  Airways are miles wide.  You can be off course a bit and nobody will really care.  I also use more than one navigation system at all times.  My Approach rated GPS was the primary form of navigation for much of the trip, but I was also cross checking it against nearby VOR stations.  This helped because some legs I was flying were well over 100 miles long, and it was easier to figure out where I was on the charts by grabbing a cross radial from a VOR than it was to try and figure out how far down an airway I was when the GPS read 75 miles from some distant fix. 

I also kept track of the time, my headings, and what the winds aloft were.  Given that data, I could have had a total electrical failure and I still would know where I was (with less accuracy) even though there were many minutes where I felt like I was on the inside of a ping pong ball. 

The main reason I don't recommend having a cell phone on in flight is because mine reverted to analog mode and wore down my batteries pretty badly.  By the time I landed in Tampa (late) I was exhausted from nearly 10 hours of flying in headwinds, and my phone batteries were quite dead.  Were it not for the kindness of a couple other late arrivals, I'd have spent the night in my airplane.

That said, the problem isn't the electronic gagets you know about.  It's the ones you don't know about that represent the hazard.  14 CFR 91.21 implies that the Pilot in Command should be advised of the status of all portable electronic devices.  If someone tries to use such a device illicitly, I'd make sure thier arrival was bumpy indeed.

Do electronic gadgets threaten airplanes after all?

President4242

Tue Apr 11 13:23:37 -0700 2006

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I can't believe that out of 20 replies, nobody mentioned that Discovery Channel's Mythbusters episode on this re-ran just last Sunday; and the results?  LIKELY cause of interferance as near as they could tell- but if your plane is built properly with correct shielding on the wires, the interferance disappears.  Their test, like all Mythbusters tests, was entertaining to say the least, and fourfold:

1. Faraday Cage, standard Avionic instrumentation:  Only cell phones operating in the 800-900 Mhz band or simulated with a radio frequency generator caused any problem,  but just turning on the phone made the dials swing.
2. Cab from a Piper Cub on the back of a pickup truck driven around a parking lot close to an airport, same homebrew instrumentation board- dials were swinging so wildly from the motion of the truck that they couldn't figure out if the cell phones were doing anything at all.
3. Same truck, same instruments, parked- cell phones would make the dials swing, same bands as in the Faraday Cage.
4. Cell phones and frequency generator in the back of a parked and chartered Lear Jet- No interferance detected at all.

Their conclusion- it would probably take a problem with the plane's wiring to cause interferance- some sort of break in the shielding of the coax to the GPS or something of that sort.  But far more than just the GPS went wronng with unshielded wiring- and the federal law is probably based on the "Better safe than sorry" idea that they simply can't test all of the new cell phones coming out on the market every hour of every day.

 

Do electronic gadgets threaten airplanes after all?

Lindsey

Tue Apr 11 16:47:52 -0700 2006

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So, isn't it always like that with crashes?  Many things go wrong cascading into one another and the chain could have been stopped at almost any step

Do electronic gadgets threaten airplanes after all?

President4242

Wed Apr 12 06:45:14 -0700 2006

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Yep- and since it's easiest to stop it at the cell phone in the passenger's hand (you're NOT going to seriously consider examining a few miles of wire harness in mid-flight to see where the insulation is worn out) the decision is the correct, if annoying, one.

Do electronic gadgets threaten airplanes after all?

Kim Holburn

Thu Apr 13 07:01:00 -0700 2006

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As far as I know the problem with cell phones has always been a problem for cell phone companies - your phone sees too many cells. 

There might also be the problem that if everyone had them on in a metal tube with small windows that the phones, which boost power when they are having connection problems, all bost together you could get a lot of radio - 400 passengers - 400 radio transmitters?

No-one mentioned wifi? blue tooth?