We've all heard the announcement "switch off mobile phones and electronic devices for take off and landing".

But do we even need to switch phones off anymore? Large numbers of people have accidentally left their phone on during flight, and yet very few planes fall out of the sky.

The UK Civil Authority explains that mobile phones must be turned off during take-off and landing because they compete with signals used for ground communication between the plane and control tower.

So while they won't cause any lasting damage to a plane itself, crucial communication could be interrupted. Which could be annoying and potentially dangerous, but not "plane falls out of sky randomly because you text your mum" dangerous.

But according to a New York Times blog, the interference generated by everyone switching their phones off then on again at the same time could be a worry.

That sames blog says the radio frequencies that are assigned for aviation use are separate from commercial use and that there have never been any reported accidents from these kinds of devices being used on planes.

Still, no cigar from the CAA here in the UK. They stand by the "phones off" view.

The official CAA line reads: "Gadgets, such as laptops, tablets, MP3 players, video games etc might cause interference with aircraft communications and control systems and as such should be switched off during taxi, take off and landing and whenever instructed by the aircraft crew."

Both BA and Easyjet say mobiles must be switched off during take off and landing for these reasons, and used in flight safe mode otherwise. But as BA's press office says: "You won't get a signal, because you're too high up".

BA do have one flight where you can use your phone during the flight - the route from London City Airport to New York JFK.

if you can't bear to be disconnected for a few hours, this business class service is equipped with the OnAir on-board connectivity system which lets you use text, email and internet access during the flight.

That access is becoming popular on US domestic flights. American Airlines introduced Wi-Fi in 2009 and both Delta and Virgin America offer the service.

GADGETS: CHECK-IN OR CARRY ON?

Separately, reports have surfaced recently that Amazon Kindles are being ruined by some strong X-Ray machines. So do double-check yours when you pass it through the scanner at your local hub.

An American traveller quoted by the Daily Mail said that after passing through the x-ray scanner, her son's Kindle looked like an etch-a-sketch, adding that "the screen [was] burned so badly that even in the off position you see all of the lines and squiggles and letters".

Professor Daping Chu, from University of Cambridge Centre for Advanced Photonics, said it might not be caused by the x-ray, but by static electricity build up. He said: "You can get a buildup of static inside these machines, caused by the rubber belt".

The electricity could skew the tiny capsules filled with magnetic particles that make up the letters.

Amazon tells The Huffington Post they are not aware of any complaints, and that "exposing your Kindle to an X-ray machine, such as those used by airport security, should not cause any problems with the Kindle. Many Kindle users travel by air, and their Kindles are screened by airport security every day without issue."

But if you're still worried then check in your Kindle and revert to books.

The most important advice for carrying any kind of gadget through an airport is have them all to hand so you don't hold up the airport queue.