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Cell Phones and Air Safety
Cutie Pi writes "On the heels of this recent Slashdot story discussing Wi-Fi use on airplanes, the BBC is reporting about new evidence indicating that cell phones can interfere with airplanes' navigation systems. From the article: "In tests, compasses froze or overshot, navigation bearings were inaccurate and there was interference on radio channels." Look like like Wi-Fi and airplanes just don't mix."
Wifi uses far less power then cellphones do.
autopr0n is like, down and stuff.
Aren't cellphones already banned on commerical airliners?
Wireless I really cannot believe that 802.11b can affect telecommunication equipment in an airplane with all that shielded cable. This could be a start to restricting use of our airwaves. JV
::Cough:: Bullshit.. ::Cough::
Usually on a plane I turn my phone silent but don't turn it off, because I think it's ridiculous that it could really be harmful. I guess I was wrong?
There comes a point in time where you just have to let things go...
Most of this article are about people who are too pigheaded to obey the safety warnings and not turn off the cell phone.
So, technology isn't there yet...TURN OFF YOUR CELL PHONE IN THE PLANE!
I was on a flight where it was delayed for 30 minutes because some jackass who was too important to be bothered would not turn off his phone.
Technology isn't there yet, until it is...just follow the safety instructions.
Cell Phones don't mix with anything.
Cell + Driving = Death
Cell + Extended Use = Brain Tumor -> Death
Although they've done wonder for the Tiny-Blue-LED Industry.
Vonal Declosion
I sure hope they are using more than a compass to navigate a commercial plane.
For commercial and medical products we have to design based on certain electromagnetic immunity requirements. What's the deal with the equipment on airplanes? I realize that wireless lans probably produce a fair amount of radiation that has to be handled but that's no excuse. I would think EVERY piece of electronics in an airplane would be designed to handle far worse. Why is that stuff so fragile?
Planes are bathed in cell phone radiation just sitting at the gate and certainly during take-offs and landings in busy metro areas. People in the airports and surrounding areas certainly don't curb their use of cell phones. It doesn't make sense to suggest there's a serious danger to airplane navigation. Would we not have seen them before.
The actual incidents that it reports are about passengers causing havoc because they refuse to turn their mobiles off -- not because these mobiles are doing any actual harm.
"Wifi uses far less power then cellphones do", not correct. Become a real Electronic engineer and you will know. What moron EVER thought WiFi was suitable for use in aircraft anyway? Probably the same fool who thinks cell phones are safe up there too. WiFi plugs into the wall for the most part. Milliwatts. Get a grip.
I can't do my nails on an airplane, but they let me take all the cell phones and WiFi equipment on that I want. In fact, they make sure that they work before you can take them on.
As long as they're not pointy.
the oddest part of the BBC story is this bit: And in October, Russian businessman Sergey Lebedev was fined £2,500 after forcing a British Airways jet to abort a landing at Manchester Airport. Cabin crew spent so long arguing with him about whether he would turn off his mobile they were unable to prepare the plane So what was his actual, offence: surliness? this is a very bad report....i prefere the kind of reporting you get in Wireless Business & Technology magazine.
or even "surly" Sergey...sorry about the typo!!
How many Cellular networks do you suppose were designed to deal with phones 5 miles up in the air moving at 550 MPH? Folks - there are other technical problems with using cellphones on airplanes quite apart from the safety issues!
The article does NOT mention the age of these airplanes.... which does make a big difference since Boeing and Airbus have started shielding their equipment better in their recent airplanes
According to the register,
British Airway is set to introduce on-board broadband services next month. and Connexion By Boeing has received to go ahead from the US Federal Aviation Administration to use WiFi networks with satellite links aboard planes, after satisfying the authority that the technology is safe.
Anyway, your cell phone won't work on a plane, it goes to fast to do hand-offs between cells properly.
SCO employee? Check out the bounty
because I think it's ridiculous that it could really be harmful. I guess I was wrong?
Do you leave it on in your pocket when you fill up with "gas" (petrol) too because it's ridiculous that a spark could cause an explosion of fumes ? Do you smoke while filling the car up too ?
Put your phone next to your car antenna and turn the radio on, and turn the phone on - hear that "dut-dut-der-dut-dut-der-dut" pulsing ?? Notice how you get the same effect when you drive to the airport (from their radar) ? Do you figure maybe a cell-phone that can't get a signal so has upped its power output to max to try and get one, about 20 feet away from the plane's antennas is going to providea stronger pulse than the radio signal being transmitted from 5 miles away ?
I was standing on the tarmac waiting to board a flight in Pakistan, next to a 747 that was being re-fuelled (which was freaking me out anyway - the av-gas fumes were really strong), and the people behind me decided this would be a good time to light up a cigarette... (they were german, said something about being ridiculous when I told them to put their lighters away and put their "f*ckin fags out").
I spent a lot of money on booze, birds and fast cars. The rest I just squandered. - George Best
Maybe I could solder a signal amp onto my airport card and wap to get longer range?
Better yet, I mercilessly slaughter ever 2.4ghz cordless phone for causing interference with my wifi.
You can't judge a book by the way it wears its hair.
Okay, maybe keeping the cellphone on DOES interfere with the navigational systems.
But what about that announcement that says "Please turn off all electronic equipment during takeoff and landing?" How can a laptop or PDA interfere with the navigation? My wristwatch is electronic. Need I turn that off?
The airlines should absolutely not allow any devices on the plane. If you need to take your cell phone, or other equipment, it needs to be checked in and picked up later, like regular luggage. Regular luggage should be scanned for radio signals before being put on the plane. The plane should be equipped with any devices, phones, WiFi computers, etc, that with the push of a button in the cockpit are all disabled immediately.
Of course, it seems the airlines put dollar$ before lives.
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They Are Vermin Feeding On Each Other's Feces.
I Hate \.
that nice aluminum skin makes for a good shield from outside interference
I should know. I am working on a electronic module with serious EMI problems. Aluminum is a poor EM shield. You might as well have nothing at all. Iron is better.
The "dut-dut-der-dut-dut-der-dut" interference on amplifiers (and CRT screen distortion) caused by mobiles seems to only occur with GSM900 phones. I was used to it happening all the time when I lived in Australia (where use use GSM900) but I've never had it occur in the US with my GSM1900 or CDMA1900 phones.
Every time a commoner gains a new method for controlling the world, Da Man comes and stomps it out.
Demand your right to use bluetooth, 8011b, and GSM devices while the plane is taking off and landing! To do anything else is bowing down to Da Man.
Oh, and if anyone knows how I can stop paying income tax, email me. It's a terrible drain on my broadband budget.
fifth sigma, inc.
What about the genome? ;)
In my more FUD/Luddite moments, I wonder what all or the radiation will do to society over time.
By the time you've got all of the electronics and wireless LAN crap installed, what is it _really_ doing to you?
Could it be that this technology will be to us as lead piping was to Rome?
Even if harmful long-term effects were demonstrated in enough studies, would it matter? <lights up a cigarette>
Get thee glass eyes, and, like a scurvy politician, seem to see things thou dost not.--King Lear
They must have worked then because the people who died were able to call their loved ones. And we never would have found out about the brave people who rose up against their captors to take over the plane (i.e. the 'Let's roll' motto). Cell phones work in airplanes. The government would not make up these calls.
Both the airline industry and the Federal Communications Commission ban the use of cell phones aboard commercial flights. But they do it for different reasons, reasons which are contradictory and scientifically unsubstantiated, critics say. http://www.privateline.com/Cellbasics/cellphonesai rlines.html
[Fuck Beta]
o0t!
What about all the planes that are taking off from the airport in the middle of a city? Are people required to turn off their cells in the airport terminals? Are telcos not allowed to place towers near airports?
I bet those 30+ incidents reported blamed cells because they needed a scapegoat for their lack of good equipment checks.
I once heard a cell phone was blamed for starting a gas station on fire. Perhaps that would be true, except the last I checked circut boards arn't a good source of spark. Next thing you will see is women being baned from wearing makeup and good looking clothing because it is a distraction for the pilots. Give me a break
...if it's all this bad, why don't planes fall out of the sky from all the existing thousands of cell phone towers all broadcasting, and tv and radio stations and other sorts of radio wave emitting places? Why not? Is it *really* that bad, or is this FUD? Seems like if it was really that bad we would have seen mass crashes and various huge numbers of fubars by now, yes?
I am skeptical, but readily admit I don't know.
Do you leave it on in your pocket when you fill up with "gas" (petrol) too because it's ridiculous that a spark could cause an explosion of fumes ?
Ridiculous.
Do you smoke while filling the car up too ?
Not ridiculous.
SCO employee? Check out the bounty
If a cellphone can interfere with flight electronics, then it's a short step to building a cellphone-like device that deliberately does so, putting the plane and its passengers in danger. It could look like a phone, a walkman, an electric shaver - anything. Why would such an achilles heel be tolerated? Unless all this heightened security is just a sham to make people feel more secure. But that's just unthinkable, right? Guys?
"I'm sorry sir, but we're diverting to another airport."
"That so?" *beep beep boop*
The coolest voice ever.
Notice that the worker gets jail time, but the buisness man just gets fined?
I don't understand your statement, that "this could be a start to restricting our use of airwaves?" We are already restricted in many way. Regardless of whether we're talking 802.11b or setting up a radio station. There are power and frequency limits, and many regulations. And speaking from a strictly American point of view, there is no Constitutional right to airwaves.
If navigation and other electronic systems on airplanes malfunction because of consumer devices that are tens of feet away, then there is a problem with the design of airplane electronics that needs to get fixed. Otherwise, airplanes are just way too vulnerable. And transmitters can masquerade as just about any kind of electronics--if they don't get fixed, then pretty much all electronics will have to be banned for security reasons. Just more deterioration of service--"we won't fix it, we'll just make things even more uncomfortable for our customers"--and people wonder why airlines are going bankrupt.
OS Software is like love: The best way to make it grow is to give it away.
Look like like Wi-Fi and airplanes just don't mix.
/end rant
And yet you link to a story about Cell phones! Cell phones != wi-fi!
"Some fight for law. Some fight for justice. What will you fight for? One day, you will see."
Why don't you fly over here and suck my dick.
Or is little Billy's Gameboy going to crash your plane?
So that's why that plane crashed in PA.
All the people calling their loved ones to tell them that they were going to die...
If you see somebody speaking on a mobile on a plane, they're A GODDAM TERRORIST!!!111!!!!1111
There are a lot more important things in the world than your miserable life.
This is old news. Using cell phones on airplanes has always been a problem. You can't use them in some areas of hospitals either, it'll mess up the electronics that keep people alive/monitor a person's health. I don't know why they need to do a study to find out what people already know.
I love how on slashdot, the majority of five-modded posts support whatever the article says..
"Wifi doesn't really interfere" : 5-level post "Of course not, blah blah"
"Wifi has no future on planes" : 5-level post "Of course it doesn't, it interferes!"
AirPhone profits.
Simple, always follow the money.
Happens with my GSM1900 phone.
GCHQ Quantum Insert installed. If only our tongues were made of glass, how much more careful we would be when we speak
the av-gas fumes were really strong, and the people behind me decided this would be a good time to light up a cigarette
I once was at a convenience store buying some gas, when one else showed up and decided to refuel his car, too. While smoking a cigar. Which he held in the same hand controlling the pump, right next to the open gas tank.
But hey, I'm alive to tell the story, so all those signs at the pump must just be the result of a bunch of old Nervous Nellies fretting over nothing, eh?
The problem could be fixed by redesigning all aircraft communication and navigation systems to use jam-resistant modulation techniques. Don't hold your breath waiting for that to happen. Voice communications still use AM. DME, VOR and ILS are based on ancient technology.
Mea navis aericumbens anguillis abundat
make better planes! time to retire these aging old coots and their mid-20th century technology! you can turn off my cellphone when you pry it from my cold, dead... um. severed, burnt and mangled hands.
"Since 1996, pilots have reported 35 mobile phone-related safety incidents, including false warnings in the cockpit, distractions causing aircraft to stray accidentally onto runways or fly at the wrong altitude, interrupted radio communications and multiple safety systems malfunctions."
35 cases in 7 years?? How many planes fly each day??
The Adult Happy Meal - "I'm lovin' it!"
Here's a report (pdf) that discusses the interference effects of cell phones on aircraft: Interference Levels In Aircraft at Radio Frequencies used by Portable Telephones An html version is available on google.
Executive Summary
Measurements made on two types of civil transport aircraft confirm that transmissions made in the cabin from portable telephones can produce interference levels that exceed demonstrated susceptibility levels for aircraft equipment approved against earlier standards. Since aircraft equipment in this class is currently in use, and can be installed, and is known to be installed, in newly built aircraft, current policy restricting the use of portable telephones on aircraft must continue. Recommendations are made to reduce the interference risk and for further studies to understand more precisely the effects of interference to aircraft equipment arising from the use of portable telephones.
is located here: http://slashdot.org/comments.pl?sid=62964&cid=5868 862
The navigation instruments in question are extremely sensitive; that precision is required when operating in the terminal area (particularly on the approach) in clouds or other visual obstruction. Operating in such conditions is done under Instrument Flight Rules (IFR). Particularly in the terminal area, IFR operations depend on precision, with less error tolerated the closer the airplane is to landing. On final approach (200' above the ground, 1/4 mile from the touchdown zone, moving at 150 knots, for a typical airliner; some approaches can be flown entirely by instrument, without ever seeing the ground, all the way to touchdown), precision is very important; a very small error could have significant consequences.
Navigating from city-to-city is usually done with the aid of instruments regardless of conditions, but doesn't require quite so much precision--consider that, in trying to find New York, you're looking for a target several hundred square miles in area. A half-mile here or there is irrelevant.
How did they hit the buildings? Well, if you saw any video at all of any of the crashes, you might have noticed the color of the sky: blue. As in, no clouds. Without clouds or other visual obstructions, operations can be carried out under Visual Flight Rules (VFR). In short, the terrorists steered the airplanes toward the targets that they could see, visually, from many miles out!
Duh.
Moderate drunk! It's more fun that way!
Aye, it's only the recording industry that takes legal action against its own customers.
--- 11 meters/second, or 24 miles per hour - the airspeed velocity of an unladen European swallow. Really.
The government would not make up these calls.
Yeah...sure. And Santa Claus and the Easter bunny really exist too.
I've always wanted to take my GPS on a plane and check out to see if the pilot is speaking the truth when announcing the altitude, plus checking speed would be cool. Anyone the rules about a GPS on a plane?
------------------------------ SirPhreak - "It's Thinking..."
My major gripe with most of the "evidence" about cell phones and other electronics on aircraft is that it's been anecdotal, including the BBC article referenced in this /. story. The link you provide is the first study with independently verifiable data regarding the RF output of consumer portable electronics and the consequent effects on avionics.
Cell phones can work in planes. When you zip over the country, your cell phone antenna has an enormous range due to the fact that there are basically no obstructions compared to the walls and trees present on the ground. But the service providers really hate it, because you leave old and re-enter new cells at an extremely high rate, which generates a huge amound of traffic in the respective cell towers.
Switch back to Slashdot's D1 system.
You get 50 times as much radiation from background sources like the sun, the earth (plants & minerals),etc. than from any man-made source like consumer electronics.
But don't take my word for it, read the CDC study.
I sure hope they are using more than a compass to navigate a commercial plane.
They do.
The compass is there to fall back on in case the sophisticated stuff quits working for whatever reason. And yes, a cellphone can interfere with the magnetic compass. I know, I'm a private pilot and own a small aircraft. Every bit of electrically operated gear in the cabin jacks with the compass's reading. Since I *know* how the electrical equipment that's installed and certificated as part of my aircraft affects my compass, I can deal with and compensate for that since I'm intimately familiar with all that gear.
It's all the *unknown* electrical devices that are brought on board an airliner and operated by passengers, that an airline pilot doesn't need to be made to worry about and wonder how to compensate for because if the situation has deteriorated to such a bad point that he's having to use the mag compass, you want nothing to interfere with it.
Now you might want to say,"How often does everything really go wrong and the pilot have to use the old fashioned mag compass to navigate?" Well, not very often at all in fact extremely rare, but I have to ask you, "How many times have you needed the spare tire in your car"? Well, I've driven my current vehicle over 150K miles in the past 11 years and never needed it, but that still doesn't mean I'm going to remove it or let the air out of it, or not check to see if it is in roadworthy before embarking upon a long trip, so why should the airline pilots risk the integrity of their last backup spare navigation instrument just because some selfish passengers want to play with their toys on board. Hell, the passengers should consider themselves lucky they are still allowed to fly at all and not having to make do with only ground and water transportation.
You misspelled "Jet-A," which is chemically far more similar to kerosene (or kerosine, as I'm guessing you're British from your use of the term "fags" for cigarettes) than gasoline. Jet-A is far tougher to ignite than gasoline; in fact, it's very much like diesel, which requires significant pressure (or additives such ammonium nitrate) to do anything really interesting.
Nonetheless, lighting up when you have a strong fuel odor around ranks fairly high on my list of things that are A) ballsy, B) stupid, or C) All of the Above.
(Avgas actually refers to aviation gasoline, which is, in fact, a gasoline product, and therefore really hazardous. It's an important distinction in this case.)
Moderate drunk! It's more fun that way!
I was standing on the tarmac waiting to board a flight in Pakistan, next to a 747 that was being re-fuelled (which was freaking me out anyway - the av-gas fumes were really strong), and the people behind me decided this would be a good time to light up a cigarette...
1) 747s do not use Av-Gas; jet fuel is similar to diesel. You can toss a burning match into a bucket of such fuel and the match will simply go out. (The temperature required to ignite the fuel is higher than the flash point of gasoline.)
2) No matter how strong the fumes smelled, do you really think the cigarette was going to a) set the fumes ablaze and b) the resulting fireball would travel all the way to the fueling area (blowing it up, no doubt)? That seems a bit farfetched.
PS That ridiculous story about a spark from a mobile phone blowing up a gas station is a urban legend.
I want to drag this out as long as possible. Bring me my protractor.
OK, so cellphones cause trouble...I've read stories in airplane magezines where cellphones affected small-plane avionics.
BUT...to say "planes and WiFi" don't mix is inappropriate, since:
(a) the article makes no montion of WiFi
(b) WiFi is lower power
(c) Wifi is in the 2400MHz range. CDMA is 1900GHz, GSM is 900/1800/1900MHz, depending on where you are.
CLearly, if Lufthansa felt that WiFi was no threat to avionics, they wouldn't be testing it on international flights OVER WATER.
Government's idea of a balanced budget: take money from the right pocket to balance...oh who am I kidding?
There wouldn't be any reasons to keep phones on in planes anyway, because they would be short of network coverage instantly after takeoff, so one could not use them anyway.
A friend of mine has a sailplane license, and he has told me that already, that when altitude is about only 2 km and plane speed no more than some +100 km/h, the GSM network coverage will vary between perfect and none very rapidly and frequently. You can imagine what would happen in 30 000 ft, then, and yet inside an aluminium chassis of the plane - not a chance. Antennas of the access points are simply not directed to provide any coverage high above ground's surface.
Theoretically, though, there are no restrictions in using phones in private small plane aviation - at least in Finland the limitations only apply in commercial traffic.
I'm a recreational pilot, and I've had first-hand experience with mobile phone that interfere with the avionics on a light aircraft. I've not witnessed any issues with nagivation instruments being affected, but I've certainly had interference on the communication systems (radio) from the mobile phone, when, for example, I've forgotten to turn my own mobile phone off (quickly remedied, thankfully :)
:). It's very annoying.
/scarey/ :)
:)
However, it's mostly GSM phones that are the problem. When the phone detects that it's losing contact with the cell, it makes a short burst of very high energy transmissions that, on the radio, sound like 'dt-dt-dt dt-dt-dt dt-dt-dt' (morse code for SSS?
However, I've NEVER noticed this with a CDMA (okay, technically IS-95) phones, which are a lot more common in the USA (vs England and Australia which primarily use GSM now). So, the UK's test is probably more accurate for GSM phones. However, I'm also sure it's not a black/white issue, but rather a matter of proportions.
Personally, if *I* was in charge of the safety of a passenger-carrying flight, I'd want to make damn sure there wasn't ANYTHING that could adversely affect navigation, even if the chance was remote. Flying around IFR at night is
Further studies need to be done. Operators need to weigh the costs of shielding the navigation instruments against the benefit of allowing passengers to use bluetooth/WiFi on the aircraft. And, passengers need to damn well obey flight crew instructions
Wow !! A bunch of fat assed self proclaimed *geeks* (actually a black spot on geek community) have absolute faith in a dick-head spreading bush'ism on CNN/MSNBC, but they can't trust when a bunch of engineers say that using Cell phone might cause problems with aircraft avionics !!
I am an engineer (no, not communications engineer, but have fair understanding of radio communications) and I know that if getting a call on my cellphone can make my speakers sitting at ~10ft. from me start crackling... then it sure won't play nice with the sensitive and high precision guidance equipments of a passenger plane.
And well, dammit... can't you just sit back, relax and enjoy the flight rather than being engrossed with chatting with your boss or reading slashdot while on airplane !! I mean don't you have a life beyond that ?
- mritunjai
Happens with my AT&T TDMA phone on 800MHz and 1900Mhz....
During takeoff and landing, all electronic devies are banned, because they can intefere with airplanes. However, cell phones are banned from the air by the FCC, because they work too well. They don't cell phones on airplanes tying up its frequency in range of 30 base stations, which would cause interference with ground cell stations.
Have you ever heard of an airplane crashing from cell phone usage? If it was really that easy to create safety problems, I'm sure it would happen all the time. Besides, terrorists could easily bring a much more powerful brodcaster onto an airplane. The real reason cell phones are banned, is that airlines don't want competition to their really expensive phones.
Were they using their cell phones, or were they using the satellite phone in the aircraft ?
Anyone using a 2.4 ghz portable phone or 802.11b knows that microwave ovens cause interference on the 2.4 ghz band. I've never seen an commercial airplane without there. So do they make special microwave ovens just for airplanes that don't mess with the 2.4 ghz spectrum?
Creationists are a lot like zombies. Slow, but powerful and numerous. And they all want to eat our brains.
Born + living = Death at some point.
Remind me never ever to board a plane with any of you selfish fuckers who are so afraid of going without using their precious toys that they'd put the safety of their fellow passengers at risk.
The world's aeronautical authorities don't do this sort of thing for fucking fun you know. This is serious business, and some of the responses coming from know-nothing fuckwits on this forum fill me (as occasional plane passenger and as a pilot) with horror.
"Information wants to be paid"
This all goes to show just how FRAGILE everything is in electronics. In programming, it's one thing to overrun a buffer by a few bytes and wonder why some totally different part of the system takes a dump, but in electronics, you can't even debug the damn thing. Airplanes have this problem times a million because of all the noise that goes circulating around in their systems. And I truly understand their concerns. I don't want to go falling down from 50,000 feet because some jackass in row 39D's WiFi driver in Windows starts sending out all kinds of strange signals. And because Windows Sucks.
And we all know how many times we've heard that cell phones were the cause of an airplane crash! Get real people... Radio signals are logrithmic. The further you get from the source the less the output becomes. Your cell phone is going to have zero, zilch, nada impact on the plane.
re: 1) OK, so I call it Av-gas as a generic term for aviation fuel, and you know the proper name - I was just pointing out that I didn't think it was a good idea to use a flint lighter (hey, may not be real flint, but you know what I mean) when 30 feet from a tanker in nearly 40 degree heat where the fumes are making a heat-haze type shimmer.... and any idiot knows that a bucket of most petrol based fuels is much safer than the fumes. Empty tankers are more vulnerable to spark explosion than full ones.
re: 2) The fuelling area was a tanker with a bloke standing on the top 30 feet away (it was along queue, 200 people being searched to make sure they weren't carrying bombs, the irony somehow escaped Air Pakistan). The fumes were really strong, and I didn't think the guy holding the re-fuelling hose was paying much attention, so he might spill some fuel when he removes the hose - still fancy taking a chance with 4 germans with lighters and cigarette butts ?? Do you think the ban on smoking on the tarmac is just for fun ?
re: PS - maybe, but how about those pens that flash when your phone rings ? Do any of those make a spark ? Or static discharge ? Me, when I'm at a petrol station, I think the "turn off your phone signs" are reasonable... even if it's just there to stop you from being distracted and pumping fuel all over yourself...
I spent a lot of money on booze, birds and fast cars. The rest I just squandered. - George Best
I bet those Jihadists knew how easy it was to crash a plane. They might still be alive instead of being raped by Vincent Price in the 7th level of hades.
But anyways, instead of whining about the laptops, should we figure out how to isolate these instruments?
"Sir, whenever I stand up, femur bone juts out through my flesh." "Then don't stand up."
Always a good methodology of fixing potentially mortal weaknesss.
Even though I think a plane crashing because of cell phones and other electronic equipment is close to null, in some cases, I wonder if it is a scam to use and pay for the airlines services. However,I do believe there can be problems. Thinking about it, one or two cell phones or whatever may not cause a problem but what about 200 at the same time. Fortunately there are experienced pilots in the air.
Just spend time in any computer help forum and you will run across people who are helped by moving their unshielded stereo speakers, cell phones, cordless phones, tvs, etc away from their computers or wireless networks.
In fact that is usually one of the first suggestions when someone is having strange monitor/video card problems.
Think about it the next time the screen flickers, get some static, strange temporary colors, or jumps or some other unusual problem that cannot be traced.
Since so many people appear to be clueless, let us start with the basics.
Physics: Any radio transmitter's radiated power diminishes in relation to the square of the distance, meaning that transmitter can affect devices close much more than devices far away.
Any radio receiver is also a transmitter. Any complex electronic device is a transmitter, unless properly shielded. Any piece of conductor is an antenna for radio frequency energy of several frequencies.
What this means, is that your cellphones, radios, computers, mp3 players etc. transmit energy, that _might_ be picked up by some piece of wiring in the airplane and be transmitted to some device where it messes up things. Your laptop may be shielded, but your mouse and headphone cords may act as antennas and carry the signals outside the computer.
Since airplanes are expensive and certifying stuff to put into that plane is also expensive, they fly with technology that is several decades old. If you want to change that technology, the price will be transferred to the price of the ticket (somebody has to pay it, companies do not have money lying around just because they are companies and for example most US carriers are currently losing, not making money).
So when the technical people who are supposed to know about these things say that you should not use certain types of electronics in the plane, there is a reason for it. High school physics might tell you how radios are supposed to work, but the real world is more complex than that.
Now it might be that the plane is new and has shielded electronics or it might be that your particular piece of kit does not emit radiation. This does not matter, it is impossible in practice to have a list of allowable plane/electronics combinations, it is much more safer to just forbid everyhing.
Radio interference is a subtle thing and not always obvious. There is not just the carrier frequency and the harmonic frequencies. There are also the frequencies that appear from the coding of the data, particular data patterns, internal frecuencies that escape through the antenna etc.
It is not likely that the RF interference would cause a plane to just drop out of the sky. But it could affect navigation instrumentation, causing for example the plane to fly in an altitude, that is reserved for planes going the other way. Which does not usually cause an accident, because there are also other safeguards, but it reduces the margin of safety.
Personally, I make always sure that I have plenty of margin in whatever I do. I do not like scenarios where a single mistake could kill me. And I do not like it when other people make that decision for me, without telling me.
The cell phone system is also not happy about having a handset which is visible to a large amount of base stations at the same time. One phone can tie up a lot of slots or frequencies. Handovers can also be problematic.
And contrary to some comments, I am not aware of any area of the world where the authorities allow using cellular phones in flight, based on few trips over recent years in Europe, Asia and South America. Sometimes the use of phones is allowed on ground, with a specific permission from the plane's captain.
kiravuo
and your cell phone is right inside the fucking plane, dickwad.
I have a friend who used to work for Motorola and another friend who is a pilot and have disscussed this many times with both of them. The pilot friend has confirmed that in reality there are no issues with cell phones, or almost any other consumer wireless technologies aboard aircrafts. It does introduce some risk when flying under instrument flight only, but cause no problems during normal cruising. With this information I was left wondering why they are banned in most commercial planes. My friend from Motorola explained that when the cell phone system was designed it was not designed to hand off calls from one tower to another tower for a phone traveling at such great speeds. In fact if you drive too fast on the road (something over 140MPH in testing) you will also have problems. Planes are flying high causing you to access multiple cells at once and you are moving to fast for the handoff to occur from one tower to another. For this reason cell phones have been restricted on commercial planes. In fact amateur radios which put out far more power than a cell phone or wifi cards are allowed to be used on planes pending the pilots permission, this confirms that it's not an issue as it is not prohibited by FCC rules. It's not reallly an interference problem, it's a policy and cell technology problem.
I'd imagine an overhaul to "cell proof" all commercial planes would cost the already struggling air industry more than they can handle.
So? It's supposed to be a free market--let them go out of business if they can't provide necessary security and robustness at a competitive price. Let's also stop the government subsidies for security, air traffic control, noise abatement, airports, etc.
Did you read the very first sentence?
"This public health statement tells you about ionizing radiation and the effects of exposure. It does not tell you about non-ionizing radiation, such as microwaves, ultrasound, or ultraviolet radiation."
This doesn't count any electromagnetic radiation. For example radio waves, or your cell phone. What it does count is "radioactive" radiation.
This study says that you get radioactive radiation from your natural sources (Carbon 14) then from man-made ones. i.e., that nuclear plant nearby, or your smoke detector.
I'm not one of those who is scared of radio waves or radioactivity, and it really helps if you know what you are talking about.
Since 1996, pilots have reported 35 mobile phone-related safety incidents, including false warnings in the cockpit, distractions causing aircraft to stray accidentally onto runways or fly at the wrong altitude, interrupted radio communications and multiple safety systems malfunctions.
False Warnings in the cockpit: Pilot got a txt msg from a "friend" in his destination.
Distractions causing aircraft to stray onto runway: Flying while Yakking
Interrupted Radio Comm: "Hold on, I got a call"
Multiple Safety Systems Malfunctions: The Pilot is too busy talking on his cellphone
What a bunch of bullshit.
Hey, I'm just your average shit and piss factory.
When i sat for a while on hold with them they extolled the wonders of free wifi broadband on all flights between frankfurt and dc.... now i have to admit that's a tempting way to pass a 9 hr flight.
People, stop with this myth. Planes are rather high-tech pieces of equipment with humans behind the controls... give it a rest people.
If a compass in a plane is affected by a 0.9 watt cell phone, then that compass is going to have major problems when the pilot keys up the AM transmitter or the transponder.
When a 747 flys over a Paging Tower, does it crash?
When a plane flys near a radio station transmitter, does it crash?
When a plane flys near a cell tower, does it crash?
When a plane flys near a television tower, does it crash?
And for the idiot that says planes were built before cell phones existing, planes were built before ILS systems existed as well, you don't see planes crashing to the ground just because they don't have an ILS system on board. Jesus people, we are talking VERY low power. Ask any maint. mech. how many watts their AM transmitter puts out on the plane... cell phones and wi-fi are miniscule in terms of power.
Tell those idiotic supersticious pilots to go back to vietnam and let the new generation take over. My god people, next they'll think that "Think Hard" will cause brain waves to interfere with the fly-by-wire systems on an Airbus....
If cell phones interfere with air plane instruments, what about planes who are taking off from an international terminal were there are hundreds of people using cell phones? Why dont we see widespread failures in take off if in fact its actually a cell phone problem?
And how exactly does this happen? cell phones and wi-fi are two very different technologies, they work on different frequencies, differnt power levels and differnt types of data they transmit....how exactly do they conflict with each other?
With the number of cells that are probably going on aircraft and ringing on aircraft every day, why are there so few reports of problems? And what exactly is the evidence behind the claim that these two technologies confilct?
When i use my wi-fi card in my laptop, and my cell phone rings, i dont have any problems with my connection. Why is the only time we seem to have a problem is at an altitude of a few thousand feet?
The article dosnt make a whole lot of sense, and it dosnt supplly anything to corrberate its claims, i think i want the 10 minutes of my life i spent reading that article back.
Why are everybody going "no damn way, you'll pry this cell phone from my cold dead hands, I need scientific evidence". What about being a bit cautious, or are you all leet electrical engineers?
I have experienced cell phones interfering heavily with electronic equipment on the ground and also in flight, so this isn't a complete fabrication.
While I was flying in a dash8, the fire alarm went off, which was pretty damn scary, I tell you. Later it turned out that a cell phone recieving a call would almost always trigger the fire alaram system in a dash8.
I really don't understand why you are so negative towards this. Do you think it's some kind of airline conspiracy, forcing you to use their expensive phones?
How small a thought it takes to fill a whole life
Me: Kat, is your phone off?
Kat: Will my phone really mess up the plane?
Me: I don't know. Do you want to find out?
[Kat turns off her phone.]
My point is that almost none of us are qualified to determine whether mobile phones cause problems for aircraft. (Raise your hand if you're a certificated avionics technician.) Unless you were on one of the September 11 flights, there is not a single phone call so important that it's worth jeopardizing the safety of the flight. All of the people who are getting indignant about not being able to use their precious phones on an aircraft should step back and get some perspective. I'm an instrument-rated pilot, and if you're in my plane when I'm shooting an ILS through a 200 foot ceiling, you damn well better turn that shit off.
irb(main):001:0>
Here are 107 pages of reports by pilots and crew about electronic interference.
Some of my favorites include airplanes turning 3 miles early.
And complete loss of heading infomration.
Now most of this evidence is circumstantial, but isn't it best not test this sort of stuff on live passengers?
Some airlines are actually fine with it.
I've had no problem on Delta and United; the flight attendants have even wanted to take a look and play with it themselves. Last time I checked their policies explicitly allowed -- that check was a year ago, but I've used my GPS openly within the last few months with no problem.
American prohibits, I know.
Alaska/Horizon seem to be the strictest: not only do they ban, but they explictly mention GPS during the safety announcement. On the Horizon flight I was recently on, the crew was more emphatic about the "No GPS!" rule more than the "No Cell Phone" rule, which seemed really strange.
As for reception, it only works in a window seat, and usually only if held near the window. Now and then I've seen it able to hold lock while on the tray table.
...but at a range of tens of m I don't think so.
One thing we are told about mobile 'phones is that they emit "2 watts" - we are not told that this comes as very steep pulses peaking at 200W. Domestic microwave ovens start at 600W and work up. What you are holding against your brain-case is a third of a microwave oven.
Nevertheless a highly inefficient 200W (mostly) electric transmitter in a metal tube full of absorbtive objects like water-filled (70%) human bodies is likely not going to generate a strong enough magnetic field to seriously upset a compass tens of m away behind a metal firewall. And at a range of 10m an omni 200W electric signal isn't going to be so curious about a small needle in an electrically shielded case.
Got time? Spend some of it coding or testing
Yesterday, I watched a dude walking along the footpath in Merriwa with his GF. They could barely afford clothes (what they wore was ragged, and not in a trendy way), yet could apparently afford a mobile 'phone that flashed red, white, blue quite brightly against the guy's face as he talked, and also the spondoolies needed to keep the thing on the air.
`Hello? Is this brain on?'
Got time? Spend some of it coding or testing
hmmm... Well, I was flying a few months ago on a commuter airline, in a small (14 passenger) twin prop, and we'd been delayed at takeoff due to snow and icing.
When we were almost there, I asked the Captains when we would be landing, as my car was in the shop, and I was going to be fscked if we were too much more delayed, as I needed to call the dealer and tell them I was running behind.
The Captain looked at me, asked if I was carrying a cell-phone as carry-on, and told me to feel free to use it if I wanted to, and that it was ok with him.
*shrugs*
-- Ray
...but it'll never happen. Not on /. (-:
Got time? Spend some of it coding or testing
I once watched a guy reset an entire fuel station with his hundred-watt CB (27MHz) linear amp (antenna about 30cm from nearest pump electronics). Does that count?
Everywhere else in the world, `gas' is the hissy stuff that happens when you heat a fluid too much. Admittedly what Aussies call "petrol stations" are actually selling some bona fide gas (LPG and sometimes LNG) as well, now.
Got time? Spend some of it coding or testing
One passenger airliner did go down because the power-drain for the seat-mounted game consoles overloaded wiring and caused a fire. Not passenger electronics, but at least the passengers weren't bored. Was it worth the price?
I can't wait for the first thread blaming the Challenger firework on an astronaut using a cell phone.
Got time? Spend some of it coding or testing
What we really need is more bandwidth, and we're getting that by reducing the channel spacing (comm channels have gone from 50kHz to 25kHz, and are moving to 8.33kHz). 8.33kHz spacing provides 2280 discrete channels for voice comm, which ought to be plenty for the forseeable future (i.e. until we go to digital comm using whatever the successor-to-the-successor-of-IP is).
Actually, the FAA and industry are currently testing the NEXCOM system as a replacement for the current 25 kHz AM voice system, rather than the 8.33 kHz system the europeans are using. Even the Europeans have acknowledged that 8.33 kHz is an interim solution to the spectrum crowding problem. NEXCOM is a TDMA, digital communication system that, depending on the configuration, can provide a user with simultaneous voice and data on one channel. Up to four channels per 25 kHz are supported.
That's a pretty good article, but I have to wonder about the author who _consistently_ confuses the word "potable" with the word "poRtable". There is a significant difference: POTABLE: Overview of noun potable The noun potable has 1 sense (no senses from tagged texts) 1. beverage, drink, drinkable, potable -- (any liquid suitable for drinking: "may I take your beverage order?") Overview of adj potable The adj potable has 1 sense (no senses from tagged texts) 1. potable -- (of alcoholic beverages that are suitable for drinking; "it's an impudent young wine but I think you will find it quite potable") PORTABLE: Overview of noun portable The noun portable has 1 sense (no senses from tagged texts) 1. portable -- (a small light typewriter) Overview of adj portable The adj portable has 2 senses (first 1 from tagged texts) 1. portable -- (easily or conveniently transported; "a portable television set") 2. portable -- (of a motor designed to be attached to the outside of a boat's hull; "a portable outboard motor")
Are airlines really saying out loud, in public, that the cockpit isn't shielded from high-frequency interference from the airplane cabin?
Is that really a message they want to be sending out to terrori---err, I mean---passengers?
Dumb.
Hijacker: "Hand over control of the plane or else I'll turn these 8 cellphones all on at the same time and interfere with your controls!"
-- Dossy
Dossy's Blog
CAA Paper 2003/03: Effects of Interference from Cellular Telephones on Aircraft Avionic Equipment
Cthulhu Barata Nikto
Hmmm, you're right. Delta still allows them to be used, but only once you're in the enroute cruise phase of flight.
United's website does not mention handheld GPS units one way or the other.
WiFi uses a lot less power than cell phones, and
WiFi has already been approved for use on airplanes. What kind of stupid editor makes that
jump? Nobody said WiFi is a cell phone.
Tool
Here's a paper I just happened to read a few days ago put out by bluetooth.org on the safety of bluetooth in airplanes. It's a few years old, but is still relevant.
o cu ment/Aircraft_Safety_Report_for_Bluetooth
https://www.bluetooth.org/foundry/sitecontent/d
It's a PDF file.
by Mike Buddha -- Someday the mountain might get him, but the law never will.
...where Toby is on his cell phone on an air plane, and the flight attendant tells him he must shut off his phone, as it may interfere with the plane's navigational equipment.
He responds: "This plane costs 150 million dollars, and you're telling me I can take it down with something I got from Radio-Shack?"
--Would shielding the cockpit (maybe a Faraday cage?) alleviate these fears?
.
== WolfriderV6 == I'm willing to admit that *I just might* be wrong... Are you??
The original reason that cellphones were discouraged in aeroplanes - at least in some areas - was that since cellphones were changing basestations at a prodigious rate, it was initially difficult for cellphone companies to bill users, since the software written to syncronise with base stations wasn't designed to handle cellphones which switched every few seconds. I'm guessing, however, that this isn't a problem any more. Given that cellphones operate on very differing frequencies to aeroplane equipment, surely it's simply a problem of harmonics or badly shielded cockpit equipment which causes these conflicts?.. I've worked with a lot of military radio equipment, and it's all designed to be interoperable, and this is part of the reason military equipment is quite so expensive; it's designed NOT to intefere with anything else the army uses. In addition, obviously, the anything-else is designed not to be interfered with, since if a few stray radio transmissions were all it were to require to cause accidents, the army would be incapacitated extremely easily. Is anyone else worried by the potential terrorist threat? given that a CELLPHONE can send an aeroplane off course - and given how easy it is to sneak a cellphone turned on on board a plane - how hard would it be to smuggle equipment into a plane which interfered with cockpit electronics and transceiving equipment by design, and how much more potent would the damage which this could cause be?
I am a viral sig. Please copy me and help me spread. Thank you
Since cell phones are so harmful, how exactly did those Airphones work? Were they just as harmful to the systems or what?
Which brings me back to my earlier comment on the subject.
-- "Government is the great fiction through which everybody endeavors to live at the expense of everybody else."
I have a Nextel i95, I always know when a call is coming before my phone rings, about 2 sec. I hear the 'dt-dt-dt-dt-dt-dt-dt' from any nearby speaker.
I was working on a computer, had the cover open. Every time my phone rang the HDD in the computer would spin down and loud 'clack' sounds followed.
A blue screen of death soon followed. Sometimes just a reboot.
If these phones can crash unsheilded computers, maybe they could crash planes.
How do you shield a plane? Doesn't shielding need earth ground to be effective?
This GSM and IDEN is dangerous stuff. But I like my Nextel phone.
If the navigational instruments are so sensitive, why are they not being effected by the masses of static electricity being created on the wings as air molecules brush pass and create a electromagnetic field?!? Please don't tell me that Wifi would cause a greater effect then 40m of polarised wing span... -Marcus www.digitalive.com.au
He's right, though. Jet fuel is *much* less volatile than av-gas (which is really just high octane gasoline that they make sure is free from contaminants). You're unlikely to get jet fuel lit from an open flame or cigarette unless you *really* try. Basically you need to have a high temperature (I think the flash point of Jet A is 125-185 degrees) and/or compression. That is the reason for the contention that the fuel tank on flight 800 was able to explode because the tank and fuel was heated by the AC system.
Having said that, it's probably not a good idea to smoke around anything like that, just in case.
oh, and av-gas is *not* a generic term for aviation fuel. Try taking off in a Cessna after mistakingly fueling up with jet-a instead of av-gas. You'll take off okay, there is about enough av-gas in the fuel lines to get you through takeoff. You'll probably get about to an altitude where you'll have to find something in front of you to land on, since you're too low to safely (ha!) turn the plane around and glide back to the runway.
>How do you shield a plane? Doesn't shielding need earth ground to be effective?
No, it simply needs to be referenced to the ground of the equipment it is protecting.
For example, your car is somewhat shielded (notice how in a bad service area your phone usually cuts out when you enter the car) yet your car has no electrical contact with the ground (unless it's raining, or you installed those wacky earthing straps).
If you could be told what you can see or read, then it follows that you could be told what to say or think - BoC
Where the hell is WiFi==Cellphones????
Bah.
News For Nerds, Facts for Fakers.
recently german lufthansa announced their first 747 with built in Wireless Broadband Internet via WiFi.
That is a hotspot inside an aircraft. and they even give you a notebook if you dont have one. (In Business and first).
at least lufthansa doesnt seem to be too worried.
they also allow you to use your cellphone if there is a delay and you are waiting inside the aircraft on the ground.
all depends on how paranoid/service orientated the Airline is.
benny
Quite apart from interacting with nav systems, cell phones apparently can interact with other systems too. I was talking on a cell phone once in the cabin while the plane was still boarding. After I finished my conversation, another passenger informed me that my entire conversation (both sides) was simultaneously carried over the plane's loudspeaker system (though apparently at the usual low volume. I did not notice it during the call, but several other passengers confirmed hearing it. Anybody else ever have a similar experience? It seemed really unlikely, but technically possible at the time.
Brave people wouldn't have let the hijackers take control in the first place.
The "let's roll" crowd had just learned that several (suspiciously similar) hijacked airplanes had been slammed into buildings, incinerating the passengers. They didn't fight back until they found out that doing so was their only real hope of saving their own asses - otherwise they'd either be killed in the crash, or shot down by the military.
Brave people would *NOT* have turned completely submissive just because the hijackes were threatening to kill a few people (and possibly had slit someone's throat to prove that they weren't kidding around).
And the static fields and discharges due to the clothing being worn by people who are inches away from the avionics equipment. Inverse-square means that being 2 feet from something is much more important than something much stronger which is 20 feet away.
Rest your digital 'phone under your CRT and see what happens when it next rings. That doesn't happen with milliwatts, o ye of the stripey and cross intelligence, not to an electron beam being pushed by maybe 40-60kV inside a lightly shielded vacuum.
The phone's official power rating is an average (as in mean, not mode or median), but the peak power is considerably higher. If your phone's average power output were 200 watts, at typical RF amplifier efficiencies you would need to feed it at least 300W, which would exhaust your batteries in an eyeblink, and burn your hand (or whatever else the device was in contact with). With a peak power ratio of 200 watts and a duty cycle of 1%, the 'phone gets to output an average of 2 watts during a recalibration cycle and yet still bounce the stuffing out of your CRT's electron beam. That's how Orion gets to use uncontrolled nukes for propulsion without smearing the crew. But there are no shock-absorbers between the 'phone antenna and your head.
Now go get a life.
Got time? Spend some of it coding or testing
It's not just that the speed of the phone is too much for the transmitter handoffs, it's also that a phone that far away prevents frequency re-use in other cells. A phone on the ground is in range of maybe 3 to 6 cells, all of which are on different frequency ranges. A phone in the air is an equal distance from a lot more cells than that. Thus the frequency of the phone is blocking several other cells trying to use the same one.
A latent existence
Digital cell phones broadcast at only 200 mW, and have automatic power control. I don't know what "legal limit" power is, it's 3W for analog cellular. (Most handsets are 600 mW analog).
WiFi can be broadcast at up to 1 watt, although above 100 mW, some form of automatic power control is required.
That said - Except at the very beginning/end of a flight where extreme precision is required, airplane nav systems are pretty resilient to interference. Aerospace engineers tend to be very conservative people design-wise.
retrorocket.o not found, launch anyway?
Yes, the peak power is indeed considerably higher. But it is NOT close to 200W. Peak-to-average ratio of most cellular signals is 7-10 dB. That means a 200 mW average cell phone is at most 2 watts peak.
Now, if you're talking about the *base station*, that's a different story, since that's broadcasting to multiple receivers. Most base station amps are in the 30-45 watt average range (I should know, my current project at work is a UMTS amp in that power range.) - Peak power of those units is indeed on the order of 300W. But a unit that can develop that kind of power won't be fitting in your hand.
retrorocket.o not found, launch anyway?
The danger is in assuming all terrorists are dumb fanatics - many of them are smart, well-funded fanatics. If an airplane can be brought down by RFI, somebody is going to take a boombox, fasten in a circuit board full of jamming gear, and carry it on. It won't look suspicious in the x-ray scanner.
So, you're right, fix the airplanes. Hint: tin foil.
My God, it's Full of Source!
OUTSIDE_IP=$(dig +short my.ip @outsideip.net)
I've seen that in a number of places.
:)
On the other hand, my dual-band trimode CDMA phone (AMPS900, CDMA900/CDMA1900) doesn't interfere with anything.
OTOH, my dual-band Alinco DJ-580T (ham transceiver, 2 meters/70 cm NBFM, 2.5 watts on battery 5 watts with 12V power) can do some wonderful things to nearby electronics.
retrorocket.o not found, launch anyway?
Including of recal pulses?
While it sounds like a steep ratio for an audio signal, 10dB doesn't sound anything like steep enough for a recal. And 2 omnidirectional watts isn't going to make 30-odd very focused watts jump around to its beat like an electrified cockroach.
Got time? Spend some of it coding or testing
WTF are you talking about?
There are no "recal pulses" whatever those may be in CDMA or UMTS. We don't have to handle anything like that in any of our amplifiers. We also make a handful (not very many) GSM amplifiers, and none of those have to handle unusually high PARs either. If they did, the amplifiers would have to be huge as an RF power amplifier has to be biased to handle the highest peaks that go through it - If we had something worse than a 10 dB PAR, the amps would become huge and even more inefficient than they are now. As it is, most of our amps are only specced to deal with PARs on the order of 7-8 dB (This is what my current product has been specced.)
If you knew anything about RF design, which you apparently don't, you'd know that an amplifier has to be sized to handle the largest power peaks that go through it if you want any semblance of linearity. (Thermal design is a different issue, that's all about averages.)
retrorocket.o not found, launch anyway?
...the .phtml extension seems to have been switched off when that site was moved from the Sparc clone to the XboX. Is that better now, O sad one?
Got time? Spend some of it coding or testing
..."Zebra_X has no point to make". (-:
Got time? Spend some of it coding or testing
I bow to the Walking Barcode's superior wisdom. Sees all, knows all, friend of opticians the world over, but most of all never wrong or even vague on a point.
Got time? Spend some of it coding or testing
The transmit amp must be biased so that it can handle the peak power that will be transmitted. Otherwise, the peaks get "squished". This is the case whether it is a mobile device or the base station.
Problem with this is that biasing an amp for high power levels results in horrible efficiency at lower power levels.
For example, a Class A linear amplifier's efficiency is a maximum of 50% - This is if it is continouously operating at full rated power. If a Class A amp needs to handle 200 watts, then it must be biased with a DC power of 200 watts. If only 2 watts are being transmitted, it will consume 202 watts...
Class AB is more likely the case, the penalty for not running full power is far less, but still, there's no way a mobile device can generate a 200W pulse like you claim a GSM phone can without sacrificing large amounts of battery life.
Class C and higher = not candidates since they're not linear in any way, shape, or form. (Note that this was the one advantage of analog cellular - They used FM, which works fine when run through a class C or D amplifier since there is no information carried in the amplitude of the signal.)
retrorocket.o not found, launch anyway?