Fliers Must Turn Off Devices, but It’s Not Clear Why • Hacker News Board

Re: Fliers Must Turn Off Devices, but It’s Not Clear Why

#231

Post by lucasjung » Mon, Nov 28, 2011, 11:39 AM UTC

politician wrote: post #70

lucasjung wrote: post #37

Earlier quoted context omitted.

I currently work in developmental flight test. Any time we add a new piece of electronics to an aircraft (or replace an existing piece with a new version), be it a radio, a computer, or test instrumentation, we have to conduct an Electromagnetic Compatibility (EMC) Safety of Flight Test (SOFT) to make sure that the new equipment does not interfere in any way with avionics that are critical to safety of flight. Even i…

Could you explain to what degree incidents of unexpected interference result in dangerous failure modes? Is that sort of follow-up analysis done?

I would hesitate to use the term "dangerous failure modes." The danger generally stems from interference with key avionics during critical phases of flight. For example, if your ILS starts acting wacky right in the middle of an approach in actual IMC, you've got a problem. Likewise, if your radios become unusable due to noise anywhere in the terminal area, you've got a problem. Generally, this sort of thing is caught during the EMC SOFT, which is conducted on deck so that there is no immediate danger. Once the interference has been discovered it's basically a debugging process to figure out what the hell is going in (where is the interference originating, and how is it causing the observed effect). The plane doesn't fly again until it can pass an EMC SOFT.

Usually dangerous interference comes through hard-wired connections: a device that feeds back frequencies into the power system, which then disrupts other devices; or a device that puts noise on an avionics bus, disrupting communications on that bus.

However, sometimes a device, even a device not designed to transmit, can create significant RF interference. For example, a device that has an internal power supply or transformer of some sort. If that power supply is not working right, it might generate an oscillating signal. Maybe even the device itself is tolerant of a certain amount of oscillation in its power and so is not affected by this. Then, there just happens to be a wire inside the device, connected to the power supply that's just the right length to act as an antenna at that frequency, and now you've got an RF transmitter on your aircraft that you didn't expect or want. There are bazzillions of wires in most medium-to-large modern aircraft, and some of them are bound to be the right length to act as an antenna and receive that signal, passing interference into who-knows-what.

That example may sound highly unlikely, but it does happen.

Re: Fliers Must Turn Off Devices, but It’s Not Clear Why

#232

Post by viraptor » Mon, Nov 28, 2011, 11:39 AM UTC

bad_user wrote: post #201

fosk wrote: post #183

Earlier quoted context omitted.

Except that if you drive for 6 hours, you can't talk on the phone and you can't use your laptop. Your point doesn't make sense to me: if you're willing to drive for 6 hours, you're also willing to stop working during all that time, while if you flight you'll always find some time to work, at the terminal or in the plane.

If driving you can talk on the phone for the whole 6 hours. I did something similar at least once. Also, the driver can't use a laptop, but because of the driving activity itself, the driver is not so easily bored. Boredom is the main reason why I power on my laptop on a plane. Also, the other passengers can easily work on a laptop, watch a movie and so on. If you've got a 3G connection, the passengers can also go on…

> even I as the driven, I often find myself checking my emails while driving

Why would you ever do that? If you don't care about your safety, at least make sure you're less likely to kill others, please...

Re: Fliers Must Turn Off Devices, but It’s Not Clear Why

#233

Post by vitobcn » Mon, Nov 28, 2011, 11:40 AM UTC

Bud wrote: post #8

There is actually a very logical, sensible reason to have everyone power off and stow their devices during takeoff and landing, and this story disappointingly failed to cover it: By far the most likely time for any accidents or incidents to occur is during takeoffs and landings. If everyone has 15 objects out and is busily typing away, it's going to be tht much more difficult for flight attendants to get everyone's a…

You have a good point. However, knowing that electronic devices cannot be used, many fliers (including myself) bring their own alternative such as magazines, books, etc.

I have never seen a stewardess calling somebody's attention for reading a book. On the other hand, they'll quickly force you to stop using almost anything that has an on/off switch.

Re: Fliers Must Turn Off Devices, but It’s Not Clear Why

#234

Post by zeteo » Mon, Nov 28, 2011, 12:08 PM UTC

cperciva wrote: post #226

zeteo wrote: post #224

Earlier quoted context omitted.

Based on how Faraday cages work, I don't see how that's possible. Do you have a technical explanation or did you just pull that out of thin air?

Planes (well, most of them at least) have metal skins. The avionics -- and the passengers -- are inside this skin.

Well, you can easily see that the plane's skin is not a Faraday cage since you can make cell phone calls, use your GPS etc.

Re: Fliers Must Turn Off Devices, but It’s Not Clear Why

#235

Post by [deleted] » Mon, Nov 28, 2011, 12:20 PM UTC

Bud wrote: post #8

There is actually a very logical, sensible reason to have everyone power off and stow their devices during takeoff and landing, and this story disappointingly failed to cover it: By far the most likely time for any accidents or incidents to occur is during takeoffs and landings. If everyone has 15 objects out and is busily typing away, it's going to be tht much more difficult for flight attendants to get everyone's a…

[deleted]

Re: Fliers Must Turn Off Devices, but It’s Not Clear Why

#236

Post by jiggy2011 » Mon, Nov 28, 2011, 12:23 PM UTC

dev_jim wrote: post #116

I haven't turned off a cell phone while flying for almost ten years now. I refuse to be part of any safety or security charade.

I don't really understand the point of this unless it is done purely as an act of protest.

As soon as you make or receive a call your going to be confronted with lots of dirty looks from other passengers and an angry flight attendant who will pretty much make you turn it off anyway.

Re: Fliers Must Turn Off Devices, but It’s Not Clear Why

#237

Post by PanMan » Mon, Nov 28, 2011, 12:26 PM UTC

eps wrote: post #213

RockyMcNuts wrote: post #184

Earlier quoted context omitted.

I think maybe they didn't try hard enough LOL. If you broadcast on the radio frequency the pilot is speaking on, you can jam their transmission. If you broadcast on, say, the instrument landing frequency (ILS) frequency, the ILS needle the pilot is looking at will stay centered, no matter how much he deviates from the approach path. The pilot would undoubtedly realize something was amiss, switch comm frequencies, use…

Why not put the passenger cabin in a Faraday cage? Shouldn't be that hard or costly to do, compared.

Mostly because a faraday cage the size of the plane would be quite heavy, I guess

Re: Fliers Must Turn Off Devices, but It’s Not Clear Why

#238

Post by cperciva » Mon, Nov 28, 2011, 12:27 PM UTC

zeteo wrote: post #234

cperciva wrote: post #226

Earlier quoted context omitted.

Planes (well, most of them at least) have metal skins. The avionics -- and the passengers -- are inside this skin.

Well, you can easily see that the plane's skin is not a Faraday cage since you can make cell phone calls, use your GPS etc.

It doesn't provide complete shielding, no. But it does provide some shielding.

Re: Fliers Must Turn Off Devices, but It’s Not Clear Why

#239

Post by wlievens » Mon, Nov 28, 2011, 12:32 PM UTC

mike-cardwell wrote: post #227

T-Winsnes wrote: post #172

Earlier quoted context omitted.

Lets say we use an average of 15 minutes for a person to go to the toilet. This includes getting to and from the toilet etc. For ease of calculation we say that each person goes to the toilet twice during a workday. And there are roughly 7 billion people on the planet. That gives us 0.5 hour per person per day * 7 billion people = 3.5 billion wasted hours. At a conservative estimate of $10 per hours, that's $35 billi…

15 minutes to go to the toilet? I think you need to see a doctor.

Not if you bring your toilet computer, aka smartphone.

Re: Fliers Must Turn Off Devices, but It’s Not Clear Why

#240

Post by lucasjung » Mon, Nov 28, 2011, 12:37 PM UTC

dev_jim wrote: post #116

I haven't turned off a cell phone while flying for almost ten years now. I refuse to be part of any safety or security charade.

I have a BS in EE, a masters in Aeronautical Engineering, and fly for a living. I currently work in developmental flight test. Allow me to explain a couple of reasons why you should turn off your cell phone when flying:

1: It is not a "safety charade." See my other posts about EMC in this topic.

2: Even if you don't care about anybody else's safety, or even your own for that matter, it's still in your own best interest to turn off your phone when you go flying: if you leave your phone on, it will spend the whole flight looking for a signal, and you'll land with a dead battery.