fly me to the moon

[pollen]

I thought the use of phones on planes is only banned because they disrupt mobile networks on the ground (rather than popular theory of plane hurtling to ground due to interference of flight systems)

However an air steward on a flight back to the UK this week told the entire plane that we must not switch on our phones until well inside the terminal because of the risk of igniting avaition fuel/fumes.

Oversensitive paranoia or complete fiction on his part?

[Northernbloke]

Over sensitive paranoia - bit like not using them at petrol pumps - theoretically there is a chance of a spark form the phone antenna (if it was bared down to the metal, and was transmitting at full poer and then some whilst almost touching a piece of metal that was at "ground" potential and also while there was enought petrol vapour in the air to ignite from such a spark - highly improbable but technically possible)

As I understand it (having worked on cellphones+networks for 5 years or so a few years back) In older planes that were built before EMC (electro-magnetic compatibilty) testing came into force back in 1995 theres a possibility that the planes auto pilot/landing computers and similar automated systems can be affected by signals from the phone.

You've probably heard the chain of buzzing noises when a mobile phone is about to ring and it's sat on top of a tv or radio. This is the phone signal being inducted or "picked up" by coils/transformers/speakers etc. and being heard as audio thorugh a speaker. This can cause problems on older electronics systems that weren't designed or tested to the much higher standars we have today nowadays

So yes they're being paranoid, but in the cold light of todays "blame" culture you can't blame them for being safe instead of sorry - mind you all the american airlines i've ever flown on allow phones to be used right up until they close the door before take off and as soon as the door is opened after landing (depending on the airport/country rules + regulations)

Regards,

Northernbloke

[pollen]

thanks - it all becomes clearer

and a certain irony about the american airlines policy, in light of being better safe than sorry...

cheers

[Northernbloke]

Forgot to add that it's a popular misconception that a phone in use up in the air will disrupt mobile networks. This is handled pretty well by the networks - particularly since GSM etc replaced the old analogue TACS/ETACS mobile networks and cellsite antennas became much more directional than they used to be.

The phone will be locked onto a particular cellsite as it's taking off in the plane for example. It will only begin to look for a cell site to switch over to when it's RSSI level (received signal strength indicator) drops below a certain level set by the network operator (say -90dB) the cell site it's currently registered with has a list programmed into it by the network of neighbouring cellsites - these are the only sites that the current cellsite is allowed to "hand-off" to. The logic behind that is that if the phone is on the ground and travelling around (on a person/in a vehicle etc.) then no matter which direction it moves it should come into the area of one of the neighbouring cellsites.

Also with the impoved antennas now - most of them use a degree of "Down-tilt" to direct the signal towards the ground. The "footprint" of the site i.e. the area around the site where reception is available is very clearly defined by controlling the type and direction of the antenna and adjusting the transmitted signal level of the cellsite.

So as soon as the plane gets above a certain altitude then reception is lost becasue the cellsites antenna's prevent most of the signals from being transmitted into the sky - they're aiming at the ground where the cellphones are supposed to be.

Hope it helps - i've tried to keep it simplified, there is a lot more going on behind the scenes electronically but unless you're a scientist or network owner then it's really not of any concern.

Regards,

Northernbloke

[ieftm]

isn't the "paranoia" also part of the fact they're using 'sensitive' computer equipment on a plane (fly-by-wire) these days and they just don't want all these signals possibly disrupting the signals?

better safe than sorry I would say. you wouldn't get any reception most likely anyhow.