Dubious Airline Phone Calls




The Mathematical Impossibility

Note: The communications suites commonly used on board private aircraft do not use the same conventional cellphone technology, as purported to have been used onboard Flight 93.

The official report states that regular cellphones were used, as later confirmed by the passengers’ cellphone bills. A little homework on the mathematics & nature of cellphone networks verifies the total impossibility of making regular cellphone calls at any sort of altitude in a commercial aircraft.

Here’s why:

Cellphone networks operate with each cell covering about 10 square miles (26 square kilometers), with the transmitter in the centre of the cell. Using the formula: Area = pi r squared:

10 miles = 3.14 x (r x r) , therefore giving a radius of approximately 1.784 miles. In other words, the range of the transmitter is therefore slightly greater than 1.784 miles. To round it up, let’s call it 2 miles for the sake of arguement.

There are 5,280 feet in a mile, therefore 2 miles = 10,560 feet. Since no signal is transmitted beyond that range, normal cellphone reception at higher altitudes is clearly not possible.


Signal Strength and Shielding.

Further to this, it’s widely-known (links below) that cellphones do not receive the signal as effectively in a car, due to it being a metal tube – a Faraday cage. This phenomenon also holds in aircraft – another type of metal tube / Faraday Cage. Vans & other vehicles with a lot of metal & little glass cause more of a problem than cars with a lot of glass – the metal acts as shielding, blocking the signal reception – a problem in an aircraft, with relatively few windows. Buildings also block signal on the ground – especially old, solid stone ones – & it can be necessary to move close to a window before you get good reception again. Anything solid will block the signal, & metal provides pretty good shielding.The effective range of cellphone transmitters is therefore closer to a theoretical maximum of approximately 7,000 feet.

Additionally, I had the opportunity to test this recently, between 6th – 14th January 2006, over a total of 10 take-offs and landings at various airports: Glasgow, London Heathrow, Montreal & Calgary, using 3 cellphones, aged between brand new & 5 years old. Although subsequent theft deprived me of my exact measurements, 6,500 feet was indeed the maximum altitude at which any reception was possible – and this only on one occasion. Signal reception became impossible between 2,000 – 5,000 feet on the other 9 occasions, with all 3 cellphones losing signal almost simultaneously. I generally regained signal only 2 minutes before touchdown / lost signal within 2 minutes of takeoff – in other words, very low altitude indeed.

–Cypher 16:45, 28 May 2006 (CEST)

Transmitters for new “3G” networks are much more powerful than the conventional “2G” / “2.5G” technology that was in place / undergoing initial testing in 2001. There are several pressure groups campaigning against the new “3G” network transmitters, due to the increased power output & associated health risks (I have no knowledge of whether these health risks are real or perceived). However, following the basic precepts of radio technology, this increase in power would certainly be indicative of increased range.

This UMTS article dated 7th Sept. 2004 goes into some detail regarding the increase in range of one of the new 3G technologies:

For a city with a population of 100,000, like Erlangen in Germany, a single site rented by E-Plus on a tall chimney will be sufficient to give the entire city UMTS coverage. By way of comparison, the conventional technology would require 14 UMTS base stations to provide the same coverage. A single UHS mounted on the 234-metre tall Rheinturm tower in Dusseldorf will replace no fewer than 40 conventional base stations.

The older technology in use in 2001 could not have extended beyond the range given above, since the varying transmitter range figures that are given in more recent articles reflect the new technologies in play these days. Over a year ago, the available data on transmitter range didn’t extend to the upper limits that are now indicated, & explains why I haven’t revised my calculations since then to include technologies which, to the best of my knowledge & investigations, were at best on the drawing board – but not undergoing testing at that stage.


Further Reading:

‘Project Achilles’ – Final Report and Summary of Findings Experiments conducted on light aircraft, with a thinner skin / less shielding. Excellent article.

Cell Phones on Planes By Jon G. Auerbach, Staff Reporter of “The Wall Street Journal”.

Can Phones Really Fly? August 7, 2000, Rikki Lee, Editor of “Wireless Week”

“How Stuff Works” article explaining cellphone technology

ArticleInsider also gives the figure of 10 square miles for transmitter coverage.

Copernic Search results, looking for the keywords “cellphone reception car”, giving a reasonable overview of the extent of the shielding issue.