Josh Davis

I've always thought that a reason (although probably not the reason) for requesting that phones, ipods, ipads, kindles etc were turned off during take off and landing (or <10,000 feet as people on here say), is that, at these times, the crew would prefer that passengers' attention was on them, and any [emergency] instructions that they may need to give.

Little point shouting "BRACE" or whatever else needs to be done if half the cabin are on their phones and the rest have their headphones in.

pittpanther

At 30,000 feet (over 5 miles) I'm pretty sure a cell phone can't "see" ANY towers. Why would cell phone tower manufacturers waste power transmitting signals upwards towards the sky, when all of their users are on the ground?

You really think Verizon, AT&T, Sprint, etc have the power to convince every airline in the USA to tell their passengers to not use their cell phones in flight? Conversely, you really think airlines in the USA give two hoots about Verizon's technical flaws, and would modify their procedures as a result of these flaws?

But it's all moot, as there's no way a cell phone at cruising altitude will connect with towers 5 miles down.

jaysona

I'm not going to go a repeat what I posted just recently in another forum, but I'll say you're pretty much off the mark. You don't really know very much about the design and safety processes used for making the determinations of what is safe and how safety is determined.

You can read up on a couple of posts here and here, it is not just the electronics (LRUs) that need to be taken into account, but the hundreds of miles of cabling and connectors as well. Boeing also published a brief report in 2000 about this topic, airplanes have not changed much since then, so the report is quite relevant today.

Likelihood is low, yes, but not zero and likelihood has not been not been demonstrated to be 10 to the -9.

I suggest you read ARP4754A & ARP4761, then let's talk.

Also, as long as there are modern day airliners that have cockpit placards telling cockpit crew that the use of Wi-Fi in the cockpit is forbidden while the engines are running for the purpose of flight, I think it is prudent to keep PED rules as they are.

Calchas

At the danger of wandering off topic, GSM specifies a limit of 35 km (i.e., 22 miles) for cell tower range. This limit is imposed for timing reasons; other protocols allow a range only limited by acceptable signal-to-noise ratios. So in principle, a cell phone might be able to talk to a tower on the ground. But like you said, the towers are usually optimized for horizontal range at the expense of vertical range.

Also, the inflight wifi services provided by Gogo use adapted cell towers on the ground for backhaul.

JBEagle1000G

Thank you for adding some thoughtful evidence to this discussion.
Being IN aerospace engineering, many of the plane's systems are shielded from RF interfereance, but not ALL equipment.
Have you ever had your cell phone by your computer speakers and it makes that popping/buzzing sound?
It is possible for pilots to hear that and miss out on important coms.
Older planes are less sheilded since they were built before everyone had a cell phone.
Many of the wires in a plane are not shielded.
There's also the aspect of attention span. The flight attendants want passengers OFF their devices during takeoff/landing just in case dangerous issues arrise. Issues are far more likely during takeoff/landing and it's important the passengers are in the ready position, and paying attention in case an evacuation is quickly required.
No, cell phones, ipods, laptops won't cause a plane to plummet from the sky, but if you're arrogant enough to leave your devices on, you're doing your seatmates and pilots a disservice just because YOU believe it's bunk.
As far as I'm concerned, if there's a .1% chance someone's cell phone can cause a radio glitch or radar glitch, I want everyone's phone off.
There's NO reason you need your personal phone on for the 10 minutes of takeoff/landing. And trust me, none of you on here are THAT important, especially over the rest of us on the plane.
We're all lucky they even allow us to take our phones on the planes.
Especially with all the battery issues, and the report of a camcorder causing a fire on a ORD-STL flight today.

dgwright99

Again, not true. Interference with (for example) GPS happens all the time.

Nugget_Oz

Honeywell and Boeing have been replacing certain cockpit electronic systems which have greater risk of interference from consumer electronics.

http://online.wsj.com/article/SB1000...063260030.html

Delta Hog

After many years of this debate, and many pages of this thread, I'm tired of hearing about what is "possible". Theory takes a back seat to evidence. Over the years, we have millions of takeoffs and ground taxiing with cell phones and other electronic devices on. Let's hear some actual instances of interference, and what the consequences were.

dgwright99

Wow, never has the concept of "a little knowledge is a dangerous thing" been proven so true. [Unduly personalized remarks deleted by Moderator.]

"Phones don't transmit on frequencies used by aircraft". Completely wrong. The emissions of a cellphone (or indeed any transmitter) cover a broad spectrum. Of course the radiated power in-band is much higher than out-of-band, but for example average radiated power in the GPS band is still much higher than the received signal strength of a GPS signal, and instantaneous (rather than average) power of emissions from a cellphone can easily temporarily overwhelm a GPS receiver operating some distance away from the handset, despite that coding gain of the GPS receiver allowing it to receive signals from below the noise floor.

With GPSs in most phones handset makers have worked hard to reduce emissions far below certification limits in that band resulting in GPS being less of an issue than a few years ago (though often still an issue if a handset is connected to a cheap charger - when interference is often so bad that even the internal touchscreen doesn't work properly), but there are numerous systems with sensitivity at other frequencies. Although aircraft systems are subject to "radiated immunity" EMC testing, so are all those landline phones (and alarm clocks, and....) which buzz and click periodically when a GSM handset is nearby.

FCC regulations allow considerably higher "out of band" emissions for "intentional radiators" than the permitted emissions of "unintentional radiators" governed by FCC part B, and it is a piece of cake to build a part-B compliant device that would interfere with airplane avionics systems, so the risk of out-of-band interference from transmitting devices is higher still. The chances of such interference happening inadvertently are low, but when you have hundreds of devices operating in the same place at the same time, multiplied by millions of commercial flights per year, a one-in-a-billion chance will happen with regularity.

When cruising, there is lots of margin for error, and so the risk of occasional interference is easily manageable. Not so during takeoff and landing, and it is absolutely appropriate to proceed very cautiously, based on rigorous testing in relaxing such rules - rather than influenced by random, ignorant blow-hards.

It is natural for experts in a particular field to over-emphasize the risks that they know about, and underweight those they don't. But people drive drunk.

SeriouslyLost

I've never found that introducing facts into the discussion helps. The "cellphones will cause us all to die!!!1!1" crowd refuse to believe anything other than cell phones might cause a problem and therefore should be off. They can't point to any actual incidents that can be reproduced and are invariably Americans who studiously ignore the situation in some other countries where electronics use is permitted and planes aren't falling out of the skies, but their fervor continues unabated. (they're going to be real lost when the FAA finally catches up to the rest of the world and allows use)

Personally, I'm happy with use being banned because I don't want someone yammering away next to me for 4+ hours as I fly and I appreciate being out of touch with work for a while. But in no way do I think their use is a threat of any meaningful level to the plane. Bird strike is more common and higher on the concern list.

And yet we don't see planes falling out of the skies in other countries.

Wave your hands and thump your chest all you like about how much you know and how everyone else is an "ignorant blowhard" but the reality is that the testing has been done and various countries have tried various combinations of standards, but the simple reality is that planes aren't falling out of the skies over it. EOS.

j_the_p

Emphasis mine. This thread has not been on topic since the very first reply to the OP.

Now, back on topic, seems I can have another cocktail while onboard. ^

telloh

Even if there was a crash where cell interference was a contributing factor, it's pretty clear some here would never believe it anyway.

There are people who are convinced that God Himself could not design a transmitter that could interfere with aircraft electronics, because it's just not possible. They seem to believe airplanes are magic and immune to physical laws.

It is a fascinating observation of human behavior and denial.

crabbing

FAA Advisory Circular No: 91.21-1A:note that the FCC is concerned with interference with the cell tower system, not with the aircraft.

cestmoi123

Well, it looks like the FAA's expert panel isn't worried about the devices being on, so long as they're in airplane mode:

http://www.washingtonpost.com/busine...e9c_story.html

That seems a perfectly reasonable compromise. Turn off the transmitters when the door closes, activate the WiFi at 10k feet, but don't make people turn "off" their Kindles during taxi/takeoff/landing.

Nugget_Oz

I would prefer to rely upon the actual manufacturer of the airplane and its electronics than an "advisory panel."