What could disturb a plane's navigation system?

[RPBCACUEAIIBH]

Hi Dave!

I personally never travelled on a plane, but heard quiet a few times that electronic devices are not allowed to be turned on on a plane because they may disturb the navigation... I was wondering how so... I could imagine that phones, and other communication devices could cause some interference, since they basically use radio signals, and I watching your latest video about the raspberry getting knocked out by a flesh, I've got curious about what else could possibly disturb navigation on planes?! (If you've done a video on this before, please link in here, I didn't see it, if not then this would probably be an interesting topic.)

[Richard Crowley]

Most of the regulations against wireless consumer gadgets have little or nothing do with protection of aircraft systems.  In fact, there is currently a change to the rules underway in the USA to relax usage of wireless consumer devices on board commercial aircraft.

Note that the Mythbusters program attempted to do a program on this very topic, but they were prevented by "the authorities" (I don't remember if they specified exactly WHICH "authorities".  That is only one of several topics they wanted to do but were thwarted for various reasons.

[AG6QR]

There are a number of different types of radio navigation systems.  VOR/DME, GPS, ILS with its associated glide slope, marker beacons, etc.  Commercial aviation is rather conservative, and they tend to continue using old proven systems long after newer stuff is available.  They haven't switched everything over to GPS yet.

The ILS system is described here: http://instrument.landingsystem.com/  It's perhaps the most critical system, because it is used to guide planes to the runway.

ILS navigation depends on measuring the signal strength of variously modulated transmissions.  The plane should fly along a path where two differently modulated transmissions have equal strength.  The ILS signals are transmitted in the range of 108 MHz to 112 MHz (just above the commercial FM broadcast band), while the glide slope transmissions are at 329 MHz to 335 MHz.  Anything that transmits in these frequency ranges, intentionally or not, could, at least in theory, interfere with ILS navigation.  An oscillator on board could block the reception of the beacon, or if a device were to transmit a modulated signal, it could interfere with the navigation receiver's ability to discern the relative strengths of the two desired modulated signals.

The chances of a consumer gadget accidentally interfering with ILS is very small, but the potential consequences are so scary, most authorities have tended to be very careful.  I've flown recently, and they stopped requiring passengers to turn off all electronic devices for takeoff and landings.

[free_electron]

i've often wondered about that too.

The plane is made form conductive material and basically a huge faraday cage. The antenna's are OUTSIDE the plane.
So why would there be a problem if someone inside the cage puts crap in the spectrum ? the planes hull blocks it.

[AG6QR]

i've often wondered about that too.

The plane is made form conductive material and basically a huge faraday cage. The antenna's are OUTSIDE the plane.
So why would there be a problem if someone inside the cage puts crap in the spectrum ? the planes hull blocks it.

A faraday cage works in theory.  In theory there's no difference between theory and practice, but in practice...

Many decades ago, when I was young and foolish, and laws and rules weren't what they are now, I brought an FM radio on board a commercial airliner (727), and listened to broadcasts during the flight.  I had no trouble receiving many stations while in the air.  FM broadcast radio is very nearly the same frequency as air navigation.  Clearly, the faraday cage is imperfect at those frequencies.

Note: please DO NOT repeat my stupid experiment.

Furthermore, there's the inverse square law issue.  A navigation transmitter on the ground is tens of miles away, while equipment in the cabin is maybe tens of meters away from the navigation receiver's antenna.

I won't go so far as to say we're all doomed if someone turns on his iPad during flight.  But at the opposite extreme, it's not necessarily safe to assume that no signal could possibly escape the shielding inherent in an aluminum-skinned fuselage.

[LabSpokane]

i've often wondered about that too.

The plane is made form conductive material and basically a huge faraday cage. The antenna's are OUTSIDE the plane.
So why would there be a problem if someone inside the cage puts crap in the spectrum ? the planes hull blocks it.

Because the coax that runs inside the plane from the antenna to the radios and nav aids is not a perfect faraday cage. Hence things like shielded ignition on magnetos.

I do wonder about random people hopping on the interwebs trying to learn how to jam nav aids in flight. Let them figure it out on their own.

As for GPS, it will soon be supplemented by eLoran, due to its low susceptibility to jamming and interference.

Lastly, the new rules on mobile devices are in place and have been for some time now. They must be operated with all radios off except for wifi and the only remaining prohibition is on laptop use during takeoff and landing due to projectile concerns. Those rules have now been adopted by most international carriers as well.

[pickle9000]

I'd think rodents chewing on things would be far more dangerous. That said, hopefully no wireless / diagnostics connections to the avionics.

[sleemanj]

I personally never travelled on a plane,

Time you fixed that.  Aircraft are fun.

but heard quiet a few times that electronic devices are not allowed to be turned on on a plane because they may disturb the navigation

If you look in the cockpit of any modern airliner (in fact many modern light aircraft too) you will see a lot of electronics, including consumer grade devices.

Those regulations have little to do with technology and more to do with human factors.

[hamdi.tn]

i think we all wondered about that , but here's the thing ... if there is a 0.000000001% chance that for what ever reason my wireless device will cause a problem and risk the life of hundred person i will shut the damn thing.

[Neilm]

The plane is made form conductive material and basically a huge faraday cage. The antenna's are OUTSIDE the plane.
So why would there be a problem if someone inside the cage puts crap in the spectrum ? the planes hull blocks it.

Many years ago (c1990) there were issues with the first laptops on aircraft. As there was less EMC regulation these laptops were very EM noise. As the avionics were 10 or 20 years old, they were not designed to be screened. The avionics tends to be located near the cockpit - just about where the 1st class passengers sit. The only people who would regularly have laptops (there were very expensive back then) were the sort of people who would sit in first class - hence the rule to turn off electronic equipment.

As technology has advanced, the older flight systems have been phased out and consumer equipment now has to meet EMC emissions regulations so the instances of interference has reduced.

I did watch the Mythbusters episode where they broadcast signals in a plane on the ground - I wasn't surprised they didn't see any issue - I was a reasonably new aircraft.

[Skimask]

What about the dumbasses so busy dicking around with whatever electronic devices that they aren't paying attention to the flight attendants trying to give them information that could quite possibly save their lives?
I say let those assclowns go down in flames.  As for me, I'm shutting my stuff off and going to listen to those what those folks have to say.

Along those same lines...filling up at gas stations.  Signs say "don't use cell phones", "don't get back in your car", "shut off the engine", etc.etc.etc.  Yet here I am doing the right thing, filling my tank, while this dipshit next to me is talking away, engine running, sitting in the car, etc.etc.
I know cell phones aren't going to ignite the fuel, no shit.  I know the engine running likely isn't going to do anything, no kidding.
It's the retard sitting in the drivers seat waiting for the fuel nozzle to click off that's going to cause a problem when that fuel nozzle doesn't click off, he/she doesn't notice it, a shitload of fuel starts spilling out, runs down the side of the car, and he/she is just unlucky enough to have an exhaust pipe that exits on the same side of the car as the fuel door (ever notice most cars have those 2 items on opposite sides?), fuel contacts the hot exhaust pipe...or...better yet, dumbass babbling on the cell phone finally realizes it and yanks the fuel nozzle out of the filler neck and causes a big ol' mess.

In either case, eventually Darwin is going to win, and these idiots will weed themselves out of society...only to be replaced by another generation of morons...likely their own offspring.
Gotta cull the herd one way or another...

[Psi]

Many decades ago, when I was young and foolish, and laws and rules weren't what they are now, I brought...

I was half expecting you to say  "a 100W HAM radio transmitter on to the plane"  or something like that 


Personally i think its more dangerous to have electronics in your checked baggage than carry-on.  If something in your carry-on gets activated accidentally from turbulence no one knows it's "on" and no one can turn it "off".

But if someone is playing with a 1W CB radio in the cabin and the plane starts to fall from the sky the chances are pretty good the person will switch it off or someone will see them doing it and get them to stop.

[Richard Crowley]

It seems quite probable that any aircraft with more than 100 passengers almost certainly has at least one cell phone in someone's jacket pocket that is stowed away in the overhead bin because the passenger forgot or missed the reminder, etc. etc.  People have suggested that turning off your devices was more a social/psychological issue of making people pay attention to the cabin attendants reciting the safety mantra.

[Kohanbash]

I have heard that another problem with cell phones in the air is that you keep switching cell towers and that can cause issues to the cellular network if a plane load of people all have cell phones that are constantly switching towers.

In the USA it was the FCC that banned cell phones on planes and not the FAA.

[nixfu]

I work for an airline, let me let you in on a secret. 

In the jumpseats in the cockpit, we have 110V outlets.  We can plug our laptops in or whatever else we want, and work on them the entire flight as long as it is ok with the captain.

[SeanB]

Only issue with ILS is the detector are very simple, and only more modern ones actually use decent signal demodulation, most older ones use a version of a simple diode peak detector, or slope demodulation, so they are actually quite sensitive to RF interference. Not normally an issue as the transmitters are relatively high power, and have a very directional antenna set aimed along the desired glide slope path in any case, so received signals are pretty high so quite reliable. What is the concern on the older stuff is that RF from inside the plane can go through the cable shielding ( old cable with possible degraded joins, replaced antenna units that are not grounded well to the airframe, receiver with broken grounding strap to the mounting chassis, broken chassis ground braids) and get injected into the receiver at a high enough level to give an error, either showing the plane as too high or too low on a glide slope. That can be an issue on an old aircraft in bad weather with no other systems to show that this is happening ( like GPS altitude and position not matching the glide slope conditions, or a ground proximity warning that is premature) and thus the RF emitters were banned. By now most of the old stuff has been either upgraded or been refitted after a major airframe service, and the newer equipment has benefited from advances in technology, like a synchronous demodulator and decent filtering and such, with signal processing helping as well.

[German_EE]

So, please picture the scene. You're on an aircraft that's coming into land, there's a crosswind that's making the job REALLY difficult for the pilots and, unknown to you, that piece of electronics in your hand has an oscillator with a third harmonic that hits the Instrument Landing System frequency spot on.

500m above ground and 2Km from the end of the runway you turn it on, what's going to happen?

Chances are you'll land just fine and nobody will know, but me, I turn everything off when told to.

[GodOfVolts]

you cant in take off but when its at cruising altitude you can use eletronics       

[rs20]

The plane is made form conductive material and basically a huge faraday cage. The antenna's are OUTSIDE the plane.
So why would there be a problem if someone inside the cage puts crap in the spectrum ? the planes hull blocks it.

Yes, because a faraday cage provides an attenuation of infinity dB, at all frequencies, and no matter how big the windows/holes/gaps in the faraday cage are. Yup.

[apis]

I did watch the Mythbusters episode where they broadcast signals in a plane on the ground - I wasn't surprised they didn't see any issue - I was a reasonably new aircraft.

If I recall correctly they found no problems in the big commercial aircrafts but they also tested in an older, smaller plane and managed to affect the ILS (or som navigational instrument) adversely.