How many times have you heard this?: "At this time, all electronic devices, including cell phones and two-way pagers, must be turned off and put away. After takeoff, I'll let you know when you may use approved electronic portable devices."

Of course, those "approved electronic portable devices" won't include your cell phone, not until after you land.

The reason is that cell phones interfere with the aeroplane's electronics, right?

Well, no, actually. The risk posed by cell phones to aeroplane equipment is unknown, and will remain unknown for as long as possible.

Phones are banned for two official reasons:

1. Cell phones "might" interfere with the avionics (aviation electronics) of some aeroplanes.

2. Cell phones aloft "might" cause problems with cell tower systems on the ground.

Both of these risks are easily tested, yet somehow neither the Federal Aviation Administration (FAA) nor the Federal Communications Commission has been able to get a definitive answer in the past 20 years as to whether phone calls in flight cause these suspected problems. (The FAA is responsible for the flight safety portion of all this, and the FCC is responsible for the cell tower part.)

The government's dirty little secret is that it cultivates uncertainty about the effects of phones in aeroplanes as a way to maintain the existing ban without having to confront the expense and inconvenience to airlines and wireless carriers of allowing them.

Why airlines want the ban

The airlines fear "crowd control" problems if cell phones are allowed in flights. They believe cell phone calls might promote rude behaviour and conflict between passengers, which flight attendants would have to deal with. The airlines also benefit in general from passengers remaining ignorant about what's happening on the ground during flights, including personal problems, terrorist attacks, plane crashes and other information that might upset passengers.

One way to deal with callers bothering noncallers would be to designate sections of each flight where calling is allowed -- like a "smoking section." But the ban is easier.

Also: If real testing were done, and the nature of the problem fully understood, it would become obvious that aeroplanes could be designed or retrofitted with shielding and communications systems that would enable safe calling through all phases of flight. But that would cost money. The ban is cheaper.

However, the airlines know that some kind of plane-to-ground communication is coming, and they want to profit from it. Simply allowing passengers to use their own cell phones in flight would leave the airlines out of the profit-taking. Airlines would prefer that phones be banned while they come up with new ways to charge for communication, such as the coming wave of Wi-Fi access. Meanwhile, the ban is potentially more profitable.

Why carriers want the ban

Cell phone and tower designs are based on the assumption that at any given time, only a few cell towers will be close to any specific phone. So any given tower will use different channels than those used by other towers closest to it, but will use the same channels as towers farther away. However, when a phone is used in an aeroplane, it might have roughly equal access to two or more towers that use the same channels, which confuses the carriers' computer systems. This situation might result in interrupted calls, reduced system capacity and other problems.

Of course, this could be fixed in any number of ways, including an overhaul of the software used to manage calls between towers, but the fix would cost money. The ban is cheaper.