Q: Why can’t I use my laptop or mobile phone when the plane is taking off or landing?

A: The simple answer is that it is illegal. You are committing an offence and so is the airline if it doesn’t make you stop.

However many of the concerns airlines and safety authorities world wide held about mobile telephones or laptops in flight are becoming widely regarded by travellers and carriers and even regulators as overstated.

This may have explained why Qantas flight attendants never saw, or acted upon, the use of mobile phones by members of two rival bikie gangs who coincidentally boarded the same Cityflyer service from Melbourne to Sydney recently, and took so much offence at each others presence they called ahead to arrange what became a murder in the domestic terminal after arrival.

Or why Kevin Rudd’s apparently rude and pushy entourage is reported as emulating the PM’s propensity for air rage by refusing to shut down their electronic devices as the VIP 737 threads it way past the big hills on approach to Canberra.

According to airline sources, any largish jet between Australian cities will contain half a dozen or so mobile telephones that are left on for the entire flight by passengers who thought they were turning them off but didn’t.

How the airlines would know is unclear, but hearing a mobile phone go off somewhere in an overhead bin or coat pocket is not all that unusual on domestic flights.

It will soon become expensive however, as such phones automatically log in to new legal in flight data transfer systems that come with a charge.

Are the safety claims valid?

Only one a one in a million type of analysis, according to most experts. So your chances of inverting the Cityflyer and making it do loops while passing under the Harbour Bridge are only about 100 times better than winning Lotto.

Which is why the airlines, without exception, try to enforce the rules. Any risk of device induced danger, no matter how small, is too large. Until they can make money out of it.

How does interference occur?

Mobile phones and wi-fi enabled laptops hunt for networks. They also turn up their transmitter and receiver power to maximum output looking for a response. They can try to use the alloy fuselage of the jet as a giant send and receive antenna for this purpose.

This ensures the battery goes flat incredibly quickly, but the technical concern has always been that despite all the standards of electromagnetic interference protection built into aircraft control systems for decades, interference with navigational equipment or control systems may occur.

That fear may be absurdly overstated, but it is recognised in the regulations, and you must obey the law.

The safety regulators world wide now allow the use of mobile phones before takeoff and after landing until otherwise announced because they have no proven adverse effects on flight systems at those stages, and it is impossible to enforce a ban as people board or disembark anyhow.

Laptops and abdomens.

An open laptop in a Jetstar or Tiger flight is a physical triumph, since most people won’t even find room for their lap, but when open on any jet they obstruct access to aisles or exits, and while the jet is moving on the ground, or about to land, or until established on climb, it is a legal requirement to keep those spaces clear of obstacles in the event of an emergency evacuation.

You have about 90 seconds maximum to escape from a burning or sinking jet, or, on a bad day, one that is both burning and sinking. It is a very good rule. Keep your shoes on too. Running across burning tarmac covered with hot fragments of metal or rubber in your stocking feet is such a bitch.

Money changes everything.

As soon as Qantas nails down the commercial details it will announce a service in which mobile phones can be used for email and text messaging but not voice on many of its domestic services.

The way this works is that your iPhone or Blackberry or whatever will be linked to your service provider by a satellite link using a ‘pico-cell’ in the cabin. For a fee. Details to be announced.

The technical justification is that the pico-cell is very low powered, and ensures that devices that connect to it will do so at very low power settings too.

Qantas has mercifully decided not to allow voice links. Ryanair, which appears to hate its customers, allows its passengers to talk for about €1 per second. The good news for anyone stuck in such a cabin, as this facility is now becoming commonplace in Europe and North America, is that there are bandwidth limitations between the jet and either the satellite or ground stations the various systems use. Only about 20 passengers out of 180 on a Ryanair 737 can talk at once. Hopefully not seated all around you.

This is the beginning of a new age in in-flight communications and entertainment. As the systems get more capable airlines will offer connection fees rather than free seat back video entertainments, and you will be expected to bring your own iPod or Blackberry or laptop and pay to be connected to whatever you want via the large plasma video screen you can slave off your device using a USB cable.

While the airlines play safe and argue that while there is even the slightest doubt about electromagnetic interference from passenger devices in flight they will be banned, they are also introducing systems that will allow their safe use, for a fee, of course.