Many of the passengers on the 911 hijacked jets are reported to have made mobile phone calls to their relatives and others, telling of the hijacking or saying goodbye. However it's virtually impossible for mobile calls to be made above an altitude of around 8,000 feet, therefore these must have been faked.
The “impossible” claim is most often associated with Professor AK Dewdney, in a study of his own called "Project Achilles". He actually tried making calls at various altitudes, and concluded that "cellphone calls from passenger aircraft are physically impossible above 8000 feet and and statistically unlikely below it". There are reasons to question Dewdney’s conclusions, though. Read more here.
Phones may be used at some distance from a base station, for instance.
In practice, GSM phones cannot be used more than 35 km (22 miles) from a BTS, no matter how strong the signal.
22 miles would be over 100,000 feet. You can’t apply such a simple rule, though, because mobile networks aren’t designed to serve the skies. Others use this quote as an example of professional scepticism.
According to AT&T spokesperson Alexa Graf, cellphones are not designed for calls from the high altitudes at which most airliners normally operate. It was, in her opinion, a "fluke" that so many calls reached their destinations.
Although the full quote tells a slightly different story.
Alexa Graf, AT&T spokesperson, said systems are not designed for calls from high altitudes, suggesting it was almost a fluke that the calls reached their destinations.
“On land, we have antenna sectors that point in three directions — say north, southwest, and southeast,” she explained. “Those signals are radiating across the land, and those signals do go up, too, due to leakage.”
From high altitudes, the call quality is not very good, and most callers will experience drops. Although calls are not reliable, callers can pick up and hold calls for a little while below a certain altitude, she added.
Below a certain altitude? What might that be?
When it comes to land and air, the capabilities of a cell phone don’t change. But what makes it possible to use a handheld while in a plane 10,000 feet in the air, and why should it work there when it doesn’t work in your own neighborhood?
It all depends on where the phone is, says Marco Thompson, president of the San Diego Telecom Council. “Cell phones are not designed to work on a plane. Although they do.” The rough rule is that when the plane is slow and over a city, the phone will work up to 10,000 feet or so. “Also, it depends on how fast the plane is moving and its proximity to antennas,” Thompson says. “At 30,000 feet, it may work momentarily while near a cell site, but it’s chancy and the connection won’t last.” Also, the hand-off process from cell site to cell site is more difficult. It is created for a maximum speed of 60 mph to 100 mph. “They are not built for 400 mph airplanes.”
So it may work at 30,000 feet, although only momentarily? Apparently the New York Times agrees:
Cell phones work on airplanes? Why does the FAA discourage their use? What's the maximum altitude at which a cell phone will work?
From this morning's New York Times: "According to industry experts, it is possible to use cell phones with varying success during the ascent and descent of commercial airline flights, although the difficulty of maintaining a signal appears to increase as planes gain altitude. Some older phones, which have stronger transmitters and operate on analog networks, can be used at a maximum altitude of 10 miles, while phones on newer digital systems can work at altitudes of 5 to 6 miles. A typical airline cruising altitude would be 35,000 feet, or about 6.6 miles."
Note particularly the point that “some older phones” may work at twice the altitude of newer digital systems. Were any of those in use on 9/11? We don’t know, but it’s worth considering before you suggest the calls were “impossible”.
This question has also been addressed in The Hindu:
QUESTION: Can we receive a mobile signal while travelling in an aeroplane?
ANSWER : Mobile phones can receive signals while travelling in an aircraft, provided the base station range allows. Territory covered with GSM network is divided into hexagonal cells. The covering diameter of each hexagonal cell may be from 400 m up to 50 km, which consists of base station that provides communication-receive and transmission, and antennae.
All GSM cellular communication telephone cells are performed via these antennae and stations, which are regulated by switching centre. Switching centre provides communication between city telephone network, base stations and other cellular communication operators. Every time you switch on your cell phone, the communication is performed with the nearest base station. Hence it is possible to receive signals on cell phone while travelling in an aeroplane, provided the base station range allows.
Cell phone use during flights is still banned by regulations because it disrupts cell service on the ground and have the potential to interfere with an airplane's navigation and communication instruments.
In theory, any device that emits electronic waves — including cell phones, laptops, electronic games, pacemakers and hearing aids — has the potential to cause interference to an aeroplane.
To be safe, it is recommended banning all electronics during critical phases of a flight, which are generally considered to be during takeoff and landing, when a plane is below 10, 000 feet.
From high in the sky, a cell phone acts like a sponge, sucking capacity out of the cellular sites that carry calls. For ground users, cell phones communicate by connecting to one cell site at a time, from the air, because of the height and speed of an aircraft, the phones often make contact with several sites at once.
If allowed this would limit call capacity, which could mean less revenue. The cellular signal from the air is also especially strong, since it is unimpeded by buildings or other ground clutter. That often means it can jump on a frequency already in use on the ground, causing interruptions or hang-ups.
And airborne cellular calls are sometimes free because the signal is moving so fast between the cells that the software on the ground has difficulty, recording the call made, put the plane at risk because cellular phones can disrupt the aeroplane's automatic pilot, cabin-pressure controls.
Modern aircrafts are installed with in-flight telephones mounted on passenger seats. The carriers receive a cut of the revenue from the telephones installed onboard.
They charge about about $6 for a one minute call, more than 20 times typical cell-phone rates. Thus the airlines and telecommunications companies also have an economic incentive to keep cell phones turned off in the air.
These in-flight telephones also operate on the cellular technology — using a single airplane antenna to which the onboard phones are typically wired.
The outside aircraft antenna that carries the air-phone calls also connects to a ground-based cellular network — but with cells that are spaced much farther apart to avoid multiple phone-ground links.
And in Wireless Week:
Making Calls From The Air
By Brad Smith
September 24, 2001
c 2003, Reed Business Information, a division of Reed Elsevier Inc. All Rights Reserved.
When several passengers aboard the hijacked airliners made calls to family and spouses from their wireless phones on the now-infamous Sept. 11, it came as a surprise to many that the calls actually were completed.
Although airline passengers are warned against using their mobile phones in flight, it's fairly well-known that private airplane pilots often use regular cellular and PCS phones, even if it is illegal. Not quite as well-known, however, is that people have used their wireless phones to make surreptitious calls from the bathrooms of airliners.
The technology is there to support such airborne mobile connections. Take the Colorado company Aircell Inc., which uses FCC-approved equipment for wireless phone service.
But how does a terrestrial technology work in the sky?
First, altitude in itself is not a problem. Earthbound wireless phones can talk to base stations up to 10 miles away, depending on the terrain, while a typical passenger jet flies at an altitude of about six and a half miles. Since cell site antennas are configured to pick up signals horizontally and not from overhead, performance is usually compromised in calls from above. Nevertheless, cell sites can pick up signals from the air from great distances.
Toby Seay, vice president of national field operations for AT&T Wireless, says the technological limits to using a cell phone aboard a plane include the signal strength, potential signal inhibitors and "free space loss" as the signal gradually loses strength. The frequency used can make a difference, too. A signal using an 800 MHz cellular frequency can travel farther than a 1900 MHz PCS signal because of the different propagation characteristics of the two wavelengths.
The biggest problem with a phone signal sent from the air is that it can reach several different cell sites simultaneously. The signal can interfere with callers already using that frequency, and because there is no way for one cell site to hand off calls to another that is not adjacent to it, signals can become scrambled in the process. That's why wireless calls from jetliners don't last long, says Kathryn Condello, vice president of industry operations for CTIA. The network keeps dropping the calls, even if they are re-established later.
The phones on the back of the seats in most airplanes work similarly to a regular wireless phone. The major differences are that the antennas at the ground base stations are set up to pick up the signals from the sky, and there are far fewer stations handing off signals from one to another as a plane crosses overhead.
Also, Seay says, the airplane phones operated by AT&T Wireless and the GTE subsidiary of Verizon Communications send signals through wires to an antenna mounted on the outside of the plane. That is done to prevent interference with the plane's own radio communications, as well as to eliminate signal loss caused by the airplane's metal fuselage.
Then there’s also this report about an FCC study, talking about mobile use “at high altitude”:
An FCC study in 2000 found that cell-phone use aboard aircraft increases the number of blocked or dropped calls on the ground. That's because at high altitude, cellular signals are spread across several base stations, preventing other callers within range of those base stations from using the same frequencies.
Backing up these claims are further reports about people using their phones in flight. These are stories from 9/11:
Downs, a software salesman, learned of the terrorist attacks while on a commercial flight returning home from South America. The captain explained that "terrorist attacks on airplanes" meant they were making an emergency landing. People on board using cell phones soon discovered the true nature of the day's events.
"We found out from people using their phones that the World Trade Center was hit, and some unspecified area in Washington," Downs recalls.
...we were forced to make an emergency landing in Cleveland because there were reports that a bomb or hijacking was taking place on our plane. The pilot had radioed that there was suspicious activity in the cabin since one of the passengers was speaking urgently on his cellphone and ignored repeated flight attendant requests to stop using his cell phone while in flight.
This guy was arrested and jailed for preparing to send a text message at 31,000 feet (don’t know if he did or not, but if there was no signal you’d have expected him to turn it off as requested):
In the first case of its kind in the UK, the court had heard that Whitehouse, an oil worker, repeatedly refused to switch off his phone after being spotted with it on the Boeing 737.
Although he made no airborne calls, experts said interference from the phone could have sparked an explosion or affected the plane's navigational systems as it flew at 31,000 feet.
Here’s a pilot calling his wife, perhaps from 15,000 feet:
The pilot departed San Jose, California, on a cross-country flight to Sisters, Oregon. He obtained a standard preflight weather briefing. Visual flight was not recommended. Cumulus buildups were reported to the pilot. The pilot indicated that he may be overflying the cloud tops. He did not file a flight plan. The pilot's wife was driving to the same location and they talked by cell phone while en route. When the pilot failed to arrive at the destination a search was started. According to radar data, the aircraft was at 15,400 feet when it started a rapid descent. Radar was lost at 11,800 feet. Witnesses reported seeing the aircraft descending near vertically out of broken clouds with the engine at full power. When the aircraft was found, the right outboard wing panel from about station 110 outboard was missing. About a month later the outer wing panel was found. Analysis of the failed structure indicated a positive overload of the wing and the horizontal stabilators.
And there are various anecdotal reports, which prove nothing in themselves, but we find it hard to believe that they’re all fictional.
Although many airplanes have public "air phones," passengers flinch at the fee of $6 per minute. (Airlines get a cut of the profits, which casts suspicion on why airlines want to keep cell phones turned off in the air.) Despite government regulation, or perhaps because of it, chatting above the clouds on a cell phone has proved irresistible for some. I've seen passengers hunkered in their seats, whispering into Nokias. I've watched frequent fliers scurry for a carry-on as muffled ringing emanates from within. Once, after the lavatory line grew to an unreasonable length, I knocked on the door. A guilt- ridden teenager emerged. She admitted that she'd been in there for half an hour, talking to her boyfriend on a cell phone.
People have been communicating wirelessly from the main cabin since there have been wireless devices (never mind those overpriced satellite phones). A few years ago, I reported that the Federal Aviation Administration (FAA) was looking the other way while air travelers were firing up their personal digital assistants (PDAs) in-flight and checking e-mail. I have personally used a cell phone on a plane, and I have flown next to people who have used their cell phones, particularly when they are over a populated area or flying at a lower altitude. What is new is that the FAA appears ready to sanction equipment designed to send and receive wireless signals onboard.
I sat next to a woman who answered her cell phone at 30,000 feet, just above Mt Adams, on my way to Seattle. She answered to tell the person that she couldn't talk to them as she was on a plane.
People were using them during the whole flight. They would get constantly cut off and have to re-connect as we went over areas that didn't have service.
Yes cell phones will work on planes, my dad who is an airline pilot actually had a guy arrested because he was using his cell phone at altitude and he would not listen to the crew to put it away.
I was flying in a 757 somewhere in the 35,000 feet or thereabouts altitude when the cell phone in the briefcase of the passenger next to me started to ring. He quickly opened the briefcase and took off the battery then sheepishly looked around to see if a FA had heard it. He told me that he was using it in the terminal and forgot to turn it off.
IEEE Spectrum even ran a test to check this, and discovered cellphones were being used within commercial aircraft cabins (and not just while taking off or landing, where altitudes will be lower):
Over the course of three months in late 2003, we investigated the possibility that portable electronic devices interfere with a plane's safety instruments by measuring the RF spectrum inside commercial aircraft cabins. What we found was disturbing. Passengers are using cellphones, on the average, at least once per flight, contrary to FCC and FAA regulations, and sometimes during the especially critical flight phases of takeoff and landing.
Sceptics still point to the case of Tom Burnett. His wife says she recognised his caller ID for the first call, and we know the times these were made:
She noted the precise time for each call to the couple's California home: 6:27, 6:34, 6:45 and 6:54 a.m.
The 9/11 Commission tells us Flight 93 climbed to 40,700 feet (we believe from 36,000) feet between 9:34 and 9:38 (6:34 to 6:38 in Deena Burnett’s time), which appears to place the first call at 36,000 feet, the second at 40,700. The criticism, then, is that placing a call from 40,700 feet would have been impossible, however Jere Longman’s Among the Heroes reports that the second call was made on an Airfone.
Whatever the truth of that, we know that all the 9/11 planes did have their own built-in Airfone system, which would have no problems working at altitude (that's what they're for). If mobiles wouldn't work, then doesn't it make sense that passengers would use the phone by their seat instead? Yes, it does:
"Flight 11 attendant Betty Ong calls Vanessa Minter, an American Airlines reservations agent in North Carolina, using a seatback GTE Airfone from the back of the plane".
Some question this, pointing to press reports specifically saying that a mobile was used. Here's an example:
"At around the same time, the hijackers on flight 175 had taken control. Five minutes later, Peter Hanson, 32, a software executive travelling with his wife and two-year-old daughter, telephoned his parents in Connecticut on his mobile. Hurriedly he told the elderly couple of the knifings and the hijacking".
The problem with relying on a story like this is we don't know if the reporter verified it. Did he really try to find out whether Hanson used a mobile, or an Airfone? We don't think so, because it makes no difference to the story he's telling at all. And a sentence later in the same story confirms this:
"Those with no mobiles could only pray silently".
Whoever wrote this clearly didn't know that the planes had Airfones, and simply assumed any calls were made from mobiles instead. Therefore the report cannot be used as evidence of how they were made.
Other articles simply use terms like “cell phone” incorrectly. Here’s a graphic from the Post Gazette, for instance (http://www.post-gazette.com/images2/20011028Flight93map.jpg):
Take a look at point #12, where it’s suggested that Beamer made a “cell phone call”. Where’s the evidence for that, especially as we know he spoke to an Airfone operator? Looks to us like this is simply wrong, and another example of how reports use terms like “mobile” and “cell phone” for convenience, without verifying whether they were true.
Other stories mix the two methods of calling, but at least accept that a substantial number of calls were indeed made via Airfone:
"Now seated back in rows 30 through 34, the passengers grabbed their cell phones and in-seat phones and began calling people. Between 9:31 a.m. to 9:53 a.m. 24 calls were made from the GTE Airfones".
The final attempt to make these calls mysterious relies on reports of passengers being in the toilets, for instance. "There are no Airfones in the toilets", we're told, "so they must have been made by a mobile". But are these reports accurate?
An example from Flight 93:
"In the opposite lavatory, Jeremy Glick, an internet company worker from Hewitt, New Jersey, telephoned Lyzbeth, his wife, on his mobile".
Conclusive enough. However, look elsewhere and we find:
"Jeremy Glick, 31, used a GTE Airfone to call his wife from Flight 93".
Then there was this Flight 93 call:
"At 9.58am a 911 call - the last mobile phone contact from Flight 93 - was made from one of the airliner's toilets by passenger Edward Felt.
Glenn Cramer, the emergency supervisor who answered it, said on the day: "He was very distraught. He said he believed the plane was going down".
No reason to believe this wasn't a mobile call, but it was only minutes before the crash, and other reports suggest the plane was very low:
"Minutes before the crash, Eric Peterson of Lambertville, Pennsylvania, saw the 757 flying extremely low, maybe 300 feet from the ground".
None of this is 100% conclusive, but it does illustrate the point: there’s plenty of support for the idea cellphone calls can be made from altitude, and the Airfones were available for everyone else. Overall we see no compelling reason to believe the calls weren't genuine.