Guy,
 
I read your piece 'Time to challenge airline paranoia...' and was some-what taken back by your forthright approach to the subject.
 
As an electronic engineer who works on aerospace equipment design, and EMC test supervision, I think I have some insight into this subject.
 
Firstly the cell-phone issue is much more an issue of protecting the telephone network than the plane. Cellular systems rely on differential signal strengths between handset and ground stations. A handset in the air will have equal strength over several cells.
 
The WiFi thing is an interesting one. As for 'it would have happened already', I don't think a serious random trial has happened as yet. I use the word random guardedly since several airlines are currently developing on-board network support for passenger cabins. And there is serious interest in using 802.11.
 
Although there does not appear to be any hard evidence for issues caused by wireless devices, in fact there is a large amount of data on file, with the FAA for example. Sometimes you may see items reported in Flight magazine etc.
 
Here are some snippets.
1. On the day of a big baseball game, a pilot on an internal USA commercial flight happened to notice that his electronic compass was indicating wrongly. Investigating the cause, his crew found a number of passengers all tuned in to the same radio station on pocket radios. When they were instructed to switch off, the compass readings showed correctly. Inevitably the instrument again showed errors soon after, at which the passengers had to be threated with confiscation.
2. In an unpublicised attempt at being ahead of the field, one large airline had the passenger cabin wired throughout with CAT5. The first ground test showed that as soon as a few customers plugged into the system, the aircraft systems went hay-wire. The whole lot had to be ripped out again.
 
The issue is partly to do with the ineffectual qualification of commercial equipment for EMC. Most PC's (and especially laptops) squeeze through the EN tests by having no unessential external connections. Every unit I have seen tested was right on the limit, and connecting a network cable took radiated emissions way over.
Then there is the issue of cumulative line spectra. The radio example above was almost certainly caused by cumulative radiation of the common IF frequency from multiple sets. If one 100baseTX link is over limit, imagine the effect of one hundred of the things.
 
So, if you are intending to try some of that random testing I mentioned, please let me know in advance so that I can ground myself for the day.
 
Best regards,
RJK

Yes. I'm pretty clear in my own mind that nobody has found any WiFi dangers on an aircraft.

The phone question is a harder one. GSM/PCS phones generate radio interference far beyond what you'd expect from their power, and the reason (I'm told!) is the way TDMA works. It switches on for a 16th of a second and transmits a modulated, high-frequency pulse; and it's the start and finish of that transmit pulse of some 16 kilobits of data, which generates the "biddy-bip biddy-bip BZZZZZZZZZZ" which we've all heard when using a cellphone too close to an ordinary audio device - like a hi-fi, for example.

Unlike WiFi, that pulse is designed to reach 30 miles away in relatively cluttered areas, and the GSM spec actually allows 4W of power behind the signal. On the ground, in the open, the phone "throttles back" and only transmits at a fraction of that - which is why you'll hear the "BZZZZzzzz....." facing away to inaudibility usually. This isn't done to reduce interference, but to save battery power...

Inside a plane, the reception is poor, and the phone will whack its transmit power up to get through the windows.

There's anecdotal evidence that this can be a real nuisance to pilots. There's even anecdotal evidence that it has been potentially dangerous. The fact that pilots themselves are often guilty of switching their phones on doesn't prove they are really aware of the risks.

What is clear, is that the GSM/PCS networks aren't set up to cope with phones at 30,000 feet. So you are probably violating the terms and conditions of your phone contract if you use them five miles up, whether the danger is significant or not; and phone use ought to be restricted to emergency-only calls in flight, whatever the safety issues.

What is even more clear, is that if the airlines are right, and there is a safety risk then they are being negligent - culpably so - in allowing people to board with phones that can be switched on, even accidentally, in flight.

Pilots - I know this, but can't quote sources - are preparing to lobby against WiFi in planes. If the pilots genuinely feel that WiFi is dangerous on planes, then I think they're simply wrong.

However, it could be that they are attacking WiFi so as to prepare a precedent for banning cellphones. If so, I'd support the ban on cellphones - if enforced rigorously.

The issue of 3G phones is another one entirely; most 3G phones outside Japan are going to be WCDMA which doesn't generate the powerful on-off pulses that TDMA does, and almost certainly won't cause the same levels of interference. Don't link the two!

Edited by author 05-06-2003 02:53 PM
...or the dangers of WiFi have been assessed to be trivial on board a plane...

Surely this has already happened with Boeing Connexion, which despite the despite the branding runs on WiFi.

http://www.boeing.com/connexion/faq.html

I read your piece with interest as it's been a question I've been asking for a few years.

To further muddy the waters, the BBC has a news story today [1] about Siemens running 3G on-board planes. Given the airlines current stance, how can this be safe?

If the airlines do have to change their minds on the use of mobile phones during flights, I can imagine their going to be paying a lot of compensation to people who have been JAILED for using their phones on-board. Neil Whitehouse was sentenced to 12 months in 1999 [2] and more recently, Faiz Chopdat faced a potential two years sentence for playing tetris on his phone [3].

I was surprised that neither of these people legal defence brought forward expert witness to disprove the threat to safety.

The judge in the Whitehouse case said "the sentence should serve as a warning that mobile phone use on planes would be treated as seriously as violence on aircraft".

The Civil Aviation Authority (CAA) comment on their Web site [4] says

The CAA has conducted research which provided evidence that a mobile phone transmission on-board an aircraft may interfere with equipment including communications, navigation and flight control systems.

This doesn't sound conclusive or authoritative to me -- too many clauses -- "provided evidence", "may interfere". I agree, we need a definitive answer.

Simon Perry
http://simonperry.org/

Guy,
I'm the guy that designed the system at Britannia, so let me put you straight on a few things...

Actually all flight crew will have devices, 1800 Cabin crew get Casio PDA's, 300 odd Flight crew get laptop PC's, and 70 ground staff have ipaqs - all have removable wi-fi cards and there are access points in all crew rooms. Staff activate the devices before and after a flight to exchange data, on the plane they remove the data cards from the PDA's and replace them with data storage cards so as to conform with current CAA requirements and to provide a data back-up process for the Inland Revenue.

The main goals are to increase onboard sales, streamline internal processes, and provide the basis for better passenger service in the futurre as we can share data from the holiday/resort side of the business.

Quite a number of other airlines have expressed serious interest and you may see more of this appearing elsewhere soon....

We were preparing a full press release but you seem to have scooped us!

Let's get rid of two misconceptions.

1) When I said I didn't think phones in planes caused problems beyond annoying a few phone operators, this wasn't because I didn't know that cellphones in planes cause problems to phone operators. And
2) when I said that the airline staff threat was to ban PCs with WiFi, I didn't mean that I wanted everybody to be allowed to use GSM phones in the air.

Apart from that, the reader feedback has been very useful! - any more?