Why don’t cell phones work on airplanes at 30,000 ft? Okay so 30,000 ft is 5.6 miles high and you’re going 300 mph (ground speed) in a steel can over mostly sparsely populated land . . . so is it:
a) simply a matter that 5.6 miles is too great of distance between phone and tower?
b) you are traveling at 300 mph (ground speed) and that’s too fast for the signal to keep up with your speed
c) the airplane electronics mess up the signal?
d) most times you are traveling over sparsely populated ground (mountains, farms, ocean) that doesn’t have cell towers to begin with?
I’m thinking it’s mostly a), but does anyone know for sure?
The distance to the tower isn’t the problem; the problem is that when you’re aloft, your phone pings a couple of dozen towers instead of the few it would hit when you’re on the ground. This confuses the system.
There have been a few cases I believe where a mobile phone inside an older aircraft confused the aircraft’s electronics, but I don’t think that’s as common as The Authorities would have us believe. Aren’t there some planes now that have actual mini cell sites onboard, so that passengers can use their regular phones?
Depends on the technology and other considerations (e.g. when a tower nears it caller capacity it shrinks its range).
In theory some cell towers can extend well past 6 miles of range. And in fact people can and do use cell phones on planes. IIRC on 9/11 the people on the plane that crashed in Pennsylvania were getting information via cell phones to know they needed to try to recapture the plane.
As I understand it the main problem with using a cell phone on a plane is you pass from tower to tower too quickly. Cell towers work by passing you from one tower to the next as you move. In a plane you are zooming from tower to tower so fast the system has trouble handing you off one to the next.
Nowadays (according to a mobile phone tech guy I spoke to, who seemed to know what he was talking about) it rarely does. The system is readily able to detect the fact that you are hitting multiple cells, and so denies you service.
Some, older planes, or planes with non-perfect electronic insulation can have instrumentation issues due to cellphone usage (10 degree+ variations). This is very much a non-issue for modern, well maintained commercial planes, though.
A big issue is the system, it get hokey (like subspace said).
Sometimes well past that. Two years ago I participated in a search for a guy who crashed his airplane in a remote area and briefly had the use of his cell phone. Investigation showed that his call had been handled by a tower that was 52 miles away.
I hear varying reports on this: some say these were cellphone, others that the phones were the “airline seatback” types, specifically designed to work in flight. Anyone have the straight dope here?
I wonder what system that was. Regular GSM has a range limit of something like 32 km, which is set by the duration of packet-response windows. I think that some towers in remote areas were set up to double the length of their packet-response windows, thus halving the total data throughput on the tower, but doubling the workable range. Maybe that was involved.
CDMA is different and I don’t know the details, and I don’t know the range capabilities of any of the 3G systems. Analogue, of course, would be more limited by signal strength.
There doesn’t seem to be any difficulty at all. From the article, it appears airlines in Europe have already started allowing passengers to use phones, and unless Sen. DeFazio gets his way, this looks like it may soon be an amenity that American, United, Delta, et al., will be glad to afford you for only a nominal surcharge.
So why does the big aluminum can you’re in not act as a faraday cage and quash the signal? The fact that it’s not grounded directly to ground? Or is it more about the frequencies in use?
That article is unclear whether the airlines are installing a mini cell site on their planes for passengers to use, or simply allowing passengers to try to connect to the ground-based network outside.
I’m willing to bet that it’s the former. Airlines would be silly to pass up the revenue from charging roaming fees for the use of the satellite-based backhaul from the plane’s cell-site equipment to the ground.
When I went to Europe, there were phone handsets provided around the cabin, but they cost around $15 per minute. That probably explains why phone calls from passengers were so short on average.
Another problem would be antenna pattern. I don’t know how cell phone tower antennas are arranged, but many antennas are designed to only couple strongly with a targeted area, rather than broadcasting to and receiving from a full hemisphere (on transmission, this saves you power, and on receiving, it helps cut down noise). If so, they might only transmit to/receive from locations near the ground.
According to the 9/11 report the people on the phones were using the built-in verizon air phones or using cell when the plane was at a lower altitude. Only two were made via cell phone.
The distance is just too far for those little radios and their antenna orientations. The signal to noise ratio drops quite a bit and the phone nor the network really know what tower youre using. Toss in the doppler shift and who knows what else, and its no surprise only two went through on flight 93 and only when the plane was at very low altitudes.
No they wont wont. The article mentions OnAir Mobile. That is a specific service on planes. Its more or less a GSM mini tower on the plane with some kind of powerful uplink (perhaps sat.) Regular phones will not work.
Chronos has it closest to the mark. It is the antenna design that limits calls on airplanes.
If you look at most cell phone towers, they have big triangles at the top (at least in the US). That is because each cell is divided up into 3 sectors with a set of directional antennas to handle each sector. These types of antennas are designed to broadcast and receive over a large horizontal distance (in one direction), but a relatively small vertical distance (maybe a couple hundred feet up or down).
Here is a good visual of what a directional antenna’s pattern looks like. The antenna would be at the right side of the figure.
Several years ago I did some significant research on cell base station coverage. I’ll confirm that it’s the base station’s antenna pattern that limits the usefulness of cell phones while at altitude.
Most base stations direct the beam pattern so that it makes a pizza-slice shape with the crust-edge pointed at the horizon. This is the cost-efficient solution. Radiation going up into the sky or down in the the ground is wasted, because most cell phones will effectively be at the horizon from the point of view of the base station. (Similarly, deep space probes point their communication dish at the Sun, because at their typical distances, the Earth and Sun are effectively in the same direction.) By not radiating up or down, the station has significantly lower transmission power usage.
So, you may ask, how do airborne cell phone users manage to still make contact with the ground base stations? Two reasons: first, the beam pattern is not perfect; some radiation leaks up into the sky. If the cell phone has plenty of power, it can make a connection. Second, even if the station below you cannot make a connection, another station farther way might be able to. After all, every point in the sky is at someone’s horizon. (Actually these two reasons overlap, since altitude, atmospheric distortions and beam pattern all interact.)
From what I remember, there’s no FAA regulation forbidding cell phone operation while in flight, but you are violating FCC regulations by transmitting while airborne. Note that you are transmitting whenever your phone is on, because your phone maintains a “I’m here and available to receive calls” connection with a base station. If your cell phone provider was so inclined, they could report you to the Feds for leaving your phone on while airborne. But it’s generally not in their interest to antagonize their customers.
I’m still wondering why, when I live in a densely populated, very urban area in which cell phones have been standard equipment for just about everybody above the age of twelve, my cell phone doesn’t work in the bathroom, kitchen, or dining area–in fact, all along the southern wall of the apartment. At least the carrier did let me cancel our air cards and waive the early termination fee, because it’s a known issue.
