Yachting and Boating World forums: Airborne satnav

Quite. "Presumably".

The reason you are asked to switch things off during critical (no;- ALL)phases of flight (and not use cellphones at all) is because they just don't know what effects they may have. Thre are so far no significant numbers of airliners that were designed since cellphones and computers became commonplace, and so few, if any aircraft are protected against stray wigglies. Almost every electronic device contains an oscillator of some sort that will emit some RF. The airline and aircraft manufacturer cannot know which device you have, they cannot tell what it emits, or in what form or direction. They cannot tell where in the cabin you will be using it, or which way it will be pointing - if it is a directional emitter. They cannot evaluate local foci of RF energy that may be created by reflections from the aircraft's structure. In short, there are so many squillions of variables that it is almost impossible to achieve known safety without a design-onwards approach to screening everything on board.

So why permit laptops, portable video games (even these during take-off and landing)?

The electronics fitted to an aircraft are specifically designed for such a purpose, which is extremely costly. They then have to be certificated for use by the CAA, which is even more costly (talking several noughts for Commercial equipment) and then the installation has to be proven and certificated too. That way it is known to be safe, but at vast expense. (The landing light in a small Cessna is identical to an old fashioned tungsten filament automotive part. You can buy the same thing in an auto store for a few pence. Certificated for aviation use it will cost £25 or more. I don't think anyone has got round to halogen landing lamps in aircraft because the cost of certification is so astronomical that no profit would ever be made.)

You have heard the noise a phone makes if you put it near a radio or hi fi - imagine what the computers on an Airbus are going to make of such a random input into the flight control computer input cable, or the digital throttle control, or the flap position computer. Not a good plan, I think you will agree.

But a cellphone is an emitter.

They ask for a good reason, because it may, just may. be hazardous. There have been accidents to airliners believed caused by emissions in the cabin, and many examples of interference with systems.

On a UK registered aircraft it is a criminal offence to fail to comply with a lawful command of the Captain, which being asked to switch off is, and failure to comply in this case could also be construed as hazarding the safety of an aircraft, a very serious offense indeed.

The police do get called to deal with those few who refuse to comply, who are arrested and usually recieve large fines or worse. The courts are often draconian and very much on the Airlines' side in such matters, as they should be.

Safety comes first in the air, as it does at sea. It's just that we take your safety very seriously indeed in the air, which is why air travel is so safe, but it does require the co-operation of the passengers too - emphasis on "require"...