simplikate
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No Man's Land On Mobile Interference?

Tue Aug 30, 2011 2:21 pm

This is NOT intended to be a debate on whether interference is possible or not. Plenty of threads on that debate. Speaking from personal experience, I have left my smartphone on accidentally in my overhead bag ( in silent mode ) several times and it exchanged all kinds of data during the flight i.e. email, texts, missed calls, vm, PUSH notifications from Apps etc. Everyone I have ever asked has admitted the same.

If we are to assume a certain number of devices with whatever type of interference are left on accidentally on every flight with thousands of flights a day and tens of thousands of devices "on", then:

1) We should have more problems with aircraft interference reports

OR

2) Stricter mobile device "off" verification should be in place

It seems the current state of verbal instruction w/o action to verify "off" state is a contradiction to either side of the interference issue. Again, doesn't matter which side you embrace; just seems we're operating in no man's land. Is this a poorly thought out "habit" that just didn't get corrected due to fear OR are we too lax on the potential of dangerous interference and not enforcing the device "off" properly? I err on the side of keeping it "off" and have been more diligent, but makes me wonder.

Thoughts?
 
motif1
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RE: No Man's Land On Mobile Interference?

Tue Aug 30, 2011 2:27 pm

Seeing that UA is equipping every pilot with an iPad I would think that the interference is not an issue. Maybe it is an outdated policy but I have no idea since I am not an expert.

Are UA's iPad's WiFi only? Are they going to be in "Airplane" Mode during flight?


M1
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AF1624
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RE: No Man's Land On Mobile Interference?

Tue Aug 30, 2011 2:33 pm

I comply with the airplane mode on policy each and every time I fly because I consider that if they tell me to do so there must be a reason, even if a very small possibly outdated reason to do so.

However, I must say that I believe that this interference issue is indeed either an old problem or not a problem at all. The reason why I make this assessment is very simple : I have heard pilots telling me and read pilot stories saying that they use their personnal iPhone / iPad / Blackberry / *Place smartphone name here* to make various routine calculations during flight.

Now it is very possible that they all put their device on airplane mode when they do that. But it is just as possible that sometimes they might forget to do that. With, thankfully, no negative outcome.
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Fly2HMO
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RE: No Man's Land On Mobile Interference?

Tue Aug 30, 2011 2:41 pm

This thread won't end well...  
Quoting simplikate (Thread starter):
2) Stricter mobile device "off" verification should be in place

  

Quoting simplikate (Thread starter):
are we too lax on the potential of dangerous interference and not enforcing the device "off" properly?

  

I've worn down my keyboard enough arguing with armchair captains on here about the risks on interference and even after giving a handful of examples of instrument failures I have personally experienced as a pilot that were clearly a product of my forgetting to shut down my phone, I guess apparently the whole issue is little more than some "urban legend" or some idiotic conspiracy theory to force pax to use IFE. Please...

Ignorance is bliss I guess     
 
motif1
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RE: No Man's Land On Mobile Interference?

Tue Aug 30, 2011 2:44 pm

I always comply as well but with so many new devices emitting all kinds of signals I don't think that the rules are enforceable. We have iPhones, iPads, Kindles and 10s of other devices in pockets, bags and everywhere else. Short of FAs scanning each passenger I don't see a solution if interference is a real issue. I just hope that a/c equipment is shielded and protected sufficiently.
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simplikate
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RE: No Man's Land On Mobile Interference?

Tue Aug 30, 2011 2:50 pm

Are pilot unions make an issue of this? You are right Fly2HMO, I trust the pilot as a passenger. I just don't trust corporate processes that sometimes take a life of their own. Are pilots pleading with their companies to make stricter enforcement because they fear more interference? I'm not into conspiracies either because corp folks aren't smart enough to pull it off. I just know that the current process makes both sides wonder aloud because it doesn't seem to resolve either point of view throughly.

Quoting Fly2HMO (Reply 3):
 
tdscanuck
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RE: No Man's Land On Mobile Interference?

Wed Aug 31, 2011 12:28 am

Quoting simplikate (Thread starter):
If we are to assume a certain number of devices with whatever type of interference are left on accidentally on every flight with thousands of flights a day and tens of thousands of devices "on", then:

1) We should have more problems with aircraft interference reports

OR

2) Stricter mobile device "off" verification should be in place

There is a really wide gap between "interference that disrupts normal operation" and "interference that will kill you." Examples of 1) are legion, including multiple posters on this forum (myself included) who've experienced it firsthand. *However*, it's extremely rare for such interference to put the airplane in jeopardy. Since it is possible though, some level of precautions have to be taken. The level of precaution must be in scale with the level of the threat.

Militant termination of all RF transmission is overkill. Allowing everyone to run their devices all the time is underkill. The current state is an attempt to find the happy medium.

Quoting motif1 (Reply 1):
Seeing that UA is equipping every pilot with an iPad I would think that the interference is not an issue.

Those are certified for use on the flight deck...the *vast* majority of personal electronic devices are not. It is a huge mistake to assume that, because one device passed the required testing, another device also would.


Quoting AF1624 (Reply 2):
However, I must say that I believe that this interference issue is indeed either an old problem or not a problem at all. The reason why I make this assessment is very simple : I have heard pilots telling me and read pilot stories saying that they use their personnal iPhone / iPad / Blackberry / *Place smartphone name here* to make various routine calculations during flight.

Even if they don't put it in airplane mode, you don't always get interference. Aviation cares about very low probabilities (out past 1 in 1 billion)...the fact that something has happened safely before is no justification that it won't happen in the future. The fact that air crashes are so rare is a direct reflection of this. Also, if a pilot's device causes interference it's really easy for them to recognize that and turn it off. They don't have those options nearly so readily to hand for devices not in their personal possession.

Quoting motif1 (Reply 4):
Short of FAs scanning each passenger I don't see a solution if interference is a real issue. I just hope that a/c equipment is shielded and protected sufficiently.

Interference is a real issue. A/C equipment is generally shielded and protected. However, there are lots of aircraft systems that are *designed* to pick up RF radiation. If you put an RF transmitter of unknown power and spectrum near them they pick it up because that's what they're designed to do and it's functionally impossible to evaluate all systems against a literally infinite potential threat. It's much easier to make a good faith effort to remove the threat (turn off devices), have procedures to deal with the threat should it occur (existing flight deck non-normal procedures), and shield the equipment to the extent you can.

Tom.
 
sccutler
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RE: No Man's Land On Mobile Interference?

Wed Aug 31, 2011 4:33 am

Interference that cripples an aircraft is highly improbable - but not impossible. Why not just, y'know, turn it off?
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Starlionblue
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RE: No Man's Land On Mobile Interference?

Wed Aug 31, 2011 6:25 am

Quoting sccutler (Reply 7):
Interference that cripples an aircraft is highly improbable - but not impossible. Why not just, y'know, turn it off?

Where do you draw the line though? Once the probability is beyond 1 in 10 billion (or something) of a fatal accident, implementing systems to avoid that probability is a waste of time, money and effort. There are other possible events that are way more likely to bring the plane down.

Besides, once you're dealing with sheeple all bets are off. 
Quoting Fly2HMO (Reply 3):
This thread won't end well...

   I concur.
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MD11Engineer
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RE: No Man's Land On Mobile Interference?

Wed Aug 31, 2011 9:50 am

Quoting Fly2HMO (Reply 3):
I've worn down my keyboard enough arguing with armchair captains on here about the risks on interference and even after giving a handful of examples of instrument failures I have personally experienced as a pilot that were clearly a product of my forgetting to shut down my phone, I guess apparently the whole issue is little more than some "urban legend" or some idiotic conspiracy theory to force pax to use IFE. Please...

Ignorance is bliss I guess

You are supported by the maintenance staff. I too, while maintaining commercial aircraft, have noticed effects of mobile (cellphone) interference with aircraft electronics.

Jan
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bond007
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RE: No Man's Land On Mobile Interference?

Wed Aug 31, 2011 11:43 am

Quoting simplikate (Thread starter):
verify "off" state
Quoting sccutler (Reply 7):
Why not just, y'know, turn it off?

The problem here is also one of education. However many times the F/A might say, "switch it off", "power it down", "NOT in airplane mode", the majority of pax (and I'm quite certain of this), think pressing the button so their screen is blank, does in fact mean it is off.

I fly in the back of the plane 2-4 times every week, and every time we land, the pax next to me 'turn' their smartphones back on, and they are instantly using it. Well, smartphones take a time to boot up from a powered down state, and I rarely see this boot delay... most think they were in fact 'turned off' I believe - some knew they weren't and couldn't be bothered.

One thing that continue to irritates me is those that blatantly continue to use their phone even though they clearly heard the announcement to turn them off. This has little or nothing to do with whether they actually think it will cause any interference ... it's just they think they are too important or smart to be told what to do (and when) by a flight attendant.

Jimbo
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bhill
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RE: No Man's Land On Mobile Interference?

Wed Aug 31, 2011 6:23 pm

Here is my cut on it, regardless if the device can screw with the avionics...I do NOT want to hear you, me, my wife, the kids or anyone else on the airplane yakkin away for hours at a freakin time! If you think your are that important, hire a private plane. Enjoy the peace and quiet for a bit. If you can't be still for that long, get your doc to give you some Xanax....
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RE: No Man's Land On Mobile Interference?

Wed Aug 31, 2011 10:52 pm

Quoting tdscanuck (Reply 6):

Those are certified for use on the flight deck

Now that is REALLY interesting! Have you got a link which shows what was required for certification of the iPad and who did it?

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bond007
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RE: No Man's Land On Mobile Interference?

Thu Sep 01, 2011 3:42 am

Quoting gemuser (Reply 12):
Now that is REALLY interesting! Have you got a link which shows what was required for certification of the iPad and who did it?

Some info here:

http://www.faa.gov/other_visit/aviat...all_infos/media/2011/InFO11011.pdf

Jimbo
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tdscanuck
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RE: No Man's Land On Mobile Interference?

Thu Sep 01, 2011 4:12 am

Quoting Starlionblue (Reply 8):
Once the probability is beyond 1 in 10 billion (or something) of a fatal accident, implementing systems to avoid that probability is a waste of time, money and effort.

The two general rules (there are special exceptions) are:
1) No single failure can cause a catastrophic event, regardless of probability.
2) Any foreseeable combination of failures that would result in a catastrophic event must have a probability of less than 1 in a billion per flight hour (usually described as a failure probability of 1e-9).

Quoting gemuser (Reply 12):
Quoting tdscanuck (Reply 6):
Those are certified for use on the flight deck

Now that is REALLY interesting! Have you got a link which shows what was required for certification of the iPad and who did it?

bond007's post is the best reference. One of the companies involved in the testing is http://www.globalnavsource.com/

Tom.
 
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RE: No Man's Land On Mobile Interference?

Thu Sep 01, 2011 6:53 am

Quoting tdscanuck (Reply 14):
The two general rules (there are special exceptions) are:
1) No single failure can cause a catastrophic event, regardless of probability.
2) Any foreseeable combination of failures that would result in a catastrophic event must have a probability of less than 1 in a billion per flight hour (usually described as a failure probability of 1e-9).

So basically the designers are confident and have proven to regulators that even if all the pax have a phone and it is on, this will not bring down the plane. Good enough for me.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
tdscanuck
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RE: No Man's Land On Mobile Interference?

Thu Sep 01, 2011 4:16 pm

Quoting Starlionblue (Reply 15):
Quoting tdscanuck (Reply 14):
The two general rules (there are special exceptions) are:
1) No single failure can cause a catastrophic event, regardless of probability.
2) Any foreseeable combination of failures that would result in a catastrophic event must have a probability of less than 1 in a billion per flight hour (usually described as a failure probability of 1e-9).

So basically the designers are confident and have proven to regulators that even if all the pax have a phone and it is on, this will not bring down the plane.

Not exactly...the stipulation that all pax are told to have their electronic devices turned off is rolled into the probability calculation in option 2. If you don't tell them that and assume they're all got their stuff on all the time, the probabliity of an intereference event goes up by whatever factor left their devices on (probably a factor of between 10 and 100), which cascades through to the eventual probability of a catastrophic event. You're definitely *safer* by making the announcement but it's really hard to rigorously quantify how much...fault tree analysis is a bit of a black art.

Tom.
 
bond007
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RE: No Man's Land On Mobile Interference?

Thu Sep 01, 2011 5:52 pm

Quoting motif1 (Reply 1):
Seeing that UA is equipping every pilot with an iPad I would think that the interference is not an issue. Maybe it is an outdated policy but I have no idea since I am not an expert.

Are UA's iPad's WiFi only? Are they going to be in "Airplane" Mode during flight?

Bear in mind the cellphone regulation is more an FCC one, rather than FAA. The cell phone usage is though mentioned in an FAA Advisory Circular.

Actually FAR 91.21 bans all electronic devices .... except any "portable electronic device that the operator of the aircraft has determined will not cause interference with the navigation or communication system of the aircraft on which it is to be used."

So, the airlines themselves are the ones allowed to define exceptions to the FAR 91.21 rule. The FCC regulation means that cellphones cannot be used in flight.



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nomadd22
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RE: No Man's Land On Mobile Interference?

Thu Sep 01, 2011 6:43 pm

I wonder where flight 93 would have wound up ten years ago if there had been no cellphone use.
Anon
 
mandala499
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RE: No Man's Land On Mobile Interference?

Thu Sep 01, 2011 7:45 pm

When will interference really kill you?
I agree with Tom here...
1. There are interference which is just a nuisance... (this happens a LOT)
2. There are interference which disrupt normal operations (this is rarer)
3. There are interference that will kill you (this is very rare).

Forget #1... they rarely escalate to #2...
But, #2, can quickly escalate to #3 depending on the circumstances...
A Definite #3, is what you want to avoid all the time!

This is an issue on everyone's mind in the connectivity industry...

The key is understanding what kind of interference occuring when, that can put you at risk. This is the balanced approach Tom means I think. Without this balanced approach, bye bye onboard internet, bye bye onboard GSM service.

Apart from the safety reason of keeping your mind "alert" during critical phases of flight, there are other "technical safety reasons" for not allowing these devices on during the critical phases.

On take off, the last thing you want is interference... not because it would bring the airplane down, but because the crew will side on caution... "if it's not working well now, can we continue?" (plus you don't want to distract them with the "buzz" on their headsets just as they're coming up to V1!    _)

On landing, the last thing you want is interference... why?
1. It can be distracting to the crew if they notice it.
2. It CAN be dangerous.
If your cellphone is on, during cruise, it just searches for a cell tower. A lot of the times, they'll just scan mindlessly... and the airframe with all the other aircraft electronics will most likely prevent a latch on contact with a cell tower.
Once you get closer to the ground, this changes! The phones can start latching on to ground cell towers... That's when the problem starts... This is true even with airplanes fitted with onboard pico-cells... As you go lower, the chances of the phone latching on to a ground cell tower increases in an exponential fashion. Once below 10,000ft, they're quite likely to latch on to the ground stations... the picocells are low powered for a reason... so that all the GSM transmissions between them and the phone can be done in low power too... therefore interference risk reduction.

10,000ft on this aspect is just an arbitrary number, conveniently picked to coincide with "critical phase" for the flight crew.

And then, when your plane shoots an ILS approach, the last thing you want is the interference affecting the ILS receivers or the displays.

Quoting bond007 (Reply 10):
The problem here is also one of education. However many times the F/A might say, "switch it off", "power it down", "NOT in airplane mode", the majority of pax (and I'm quite certain of this), think pressing the button so their screen is blank, does in fact mean it is off.

Oh God, I switched off my Blackberry once, and forgot to turn the alarm off... Sometime during cruise, when I fell asleep (it was a late morning flight and I connected from a long haul), the alarm went off... and the phone switched itself on again with the cellular service on. No, I was NOT happy! I usually put it in airplane mode before switching off or leaving it on but putting it away...

Quoting bond007 (Reply 10):
One thing that continue to irritates me is those that blatantly continue to use their phone even though they clearly heard the announcement to turn them off. This has little or nothing to do with whether they actually think it will cause any interference ... it's just they think they are too important or smart to be told what to do (and when) by a flight attendant.

By April 2011, Emirates have had 5.5 million different passengers using the onboard cellular service, not one incident has occured where cellphone interference was involved. This is largely (I am told) due to the ability to use the phone above 10,000ft actually making the passengers more compliant to when they need to keep it off! They were more willing to switch it off or go to airplane mode, and wait until they can use the wavelengths again, than if they were told to keep it off all the time whilst on the aircraft.

Quoting bhill (Reply 11):
.I do NOT want to hear you, me, my wife, the kids or anyone else on the airplane yakkin away for hours at a freakin time!

Emirates' onboard GSM provider, Aeromobile, actually anticipated this problem... They, and the airline came up with guidelines on what to do and what not to do when using the cellphone on board in cruise... With that 5.5 million users, only 1 complaint has been made regarding "yakking away pax"... Aeromobile's competitor, OnAir, has also worked with its clients to come up with similar guidelines (the one I know of is Air Asia).

Quoting bond007 (Reply 13):
Some info here:

http://www.faa.gov/other_visit/aviat...1.pdf

Just keep the damn wi-fi off with whatever you use in the flight deck!
http://www.flightglobal.com/articles...dress-wi-fi-interference-with.html

Mandala499
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Starlionblue
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RE: No Man's Land On Mobile Interference?

Thu Oct 06, 2011 7:58 am

This seemed appropriate.

"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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HAWK21M
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RE: No Man's Land On Mobile Interference?

Thu Oct 06, 2011 8:55 am

There is not adequate examples of Interference in Communication & Navigation Instruments in flight due to Switched on cellphones/communication devices.....A few examples qouted may not be directly related to it.

But if the rule says switch it off.....just switch it off Until the rule is revised in future.
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tdscanuck
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RE: No Man's Land On Mobile Interference?

Thu Oct 06, 2011 2:21 pm

Quoting HAWK21M (Reply 21):
There is not adequate examples of Interference in Communication & Navigation Instruments in flight due to Switched on cellphones/communication devices.....

How many is "adequate"? There's certainly *way* more known cases of interference in comm/nav equipment than other issues we seem to fret about a great deal (multi-engine bird strikes, ETOPS, etc.).

Cell phone interference is way more common than, for example, in flight shutdowns.

Tom.
 
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RE: No Man's Land On Mobile Interference?

Thu Oct 06, 2011 3:11 pm

I think Probably one or two accidently left on will probably not be a problem but if you seddenly say its fine to use a mobile phone then the aircraft will be on approach ( Landing is dangerous time) and all of a sudden the gear will deploy and 25 people will hear it and get on their phones "honey,i'll be landing in 5mins" thenBAM!!!! 25phones all at once makes it not such a trivial matter.

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rcair1
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RE: No Man's Land On Mobile Interference?

Thu Oct 06, 2011 5:07 pm

Quoting tdscanuck (Reply 6):
something has happened safely before is no justification that it won't happen in the future.

This is a very key point that I'd like to emphasize by citing an extreme example - namely the US Space Shuttle program. If you've never read the reports by the Rogers commission on the Challenger accident, and by the Columbia Accident Investigation Board - you may find it very interesting. I poured through these some years ago both as a matter of personal interest (my father-in-law worked on the Shuttle, and I always remembered sitting and watching a launch on TV with him and hearing him say, "I hate that thing. Some day it's going to blow up." - 2 years before Challenger), and because I was dealing with a corporate structure that was trying to drive cost out, and ignoring quality as a result.

The most directly related portions are in the CAIB report on Columbia in Chapter 1 - "The Evolution of the Space Shuttle Program."

The report is too long and detailed to discuss in any significance, but the key finding is that, for political and economic reasons, the space shuttle was classified as "operational" not "experimental" - when in fact, it never left the experimental stage. One of the factors that led to both the lost of Columbia and Challenger was the willingness for NASA to accept risks based on the fact that they had not had problems in the past'

From CAIB Report - page 24 (just before section 1.5)
"More troubling, the pressure of maintaining the flight schedule created a management atmosphere that increasingly accepted less-than-specification performance of various components and systems, on the grounds that such deviations had not interfered with the success of previous flights."
The full report from the CAIB is here. http://caib.nasa.gov/news/report/default.html

Clearly - I'm not equating use of the occasional cell phone to the Challenger/Columbia disaster - however it is an interesting, though extreme, illustration of the fallacy of the "I've gotten away with it before, so it is okay" approach.

I also deal with this regularly as a Fireman. I see lots of 'accidents' that happen when people do something they've always done.

Quoting tdscanuck (Reply 6):
However, there are lots of aircraft systems that are *designed* to pick up RF radiation.

Another key point - and one that often gets forgotten. I'm not concerned about my cell phone interfering with the 'control systems' on any aircraft, but I can certainly understand how they can interfere with communication and navigation systems. I'm reminded of the every time I respond to a fire/medical emergency in my personal vehicle (happens on occasion). The Banks "IQ" system in my truck interferes with one of my tactical radio channels. The system turns on with the truck by default, so the first thing I have to do is turn it off if I want to use my fire band radio. If the IQ system is on - one of the channels I scan is covered with noise and scan locks on that channel. The Banks IQ is a bascically a windows mobile computer that interfaces to the fuel injection/engine systems to allow me to adjust power and monitor operation so is certified under FCC class 18.

Quoting Starlionblue (Reply 8):
avoid that probability is a waste of time, money and effort. There are other possible events that are way more likely to bring the plane down

Exactly what time, money and effort is being wasted?
I could see claiming this if we were delaying departures due to compliance. Or are you talking about the fact that you can't 'work' while flying. Perhaps a bit of credibility there - especially on long hall. However, in-flight internet and phone systems are addressing that.
I think that limiting use during critical flight stages is not a particularly gruesome waste of time.

Quoting bond007 (Reply 10):
think pressing the button so their screen is blank, does in fact mean it is off.

Indeed.
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RE: No Man's Land On Mobile Interference?

Thu Oct 06, 2011 11:24 pm

Quoting rcair1 (Reply 24):
Quoting Starlionblue (Reply 8):
avoid that probability is a waste of time, money and effort. There are other possible events that are way more likely to bring the plane down

Exactly what time, money and effort is being wasted?
I could see claiming this if we were delaying departures due to compliance. Or are you talking about the fact that you can't 'work' while flying. Perhaps a bit of credibility there - especially on long hall. However, in-flight internet and phone systems are addressing that.
I think that limiting use during critical flight stages is not a particularly gruesome waste of time.

I didn't mean phones should be allowed, and definitely not during take-off and landing. I meant that if one or two people have forgotten their phone on it isn't worth hunting down.
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spacecadet
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RE: No Man's Land On Mobile Interference?

Fri Oct 07, 2011 3:49 am

Quoting simplikate (Thread starter):
If we are to assume a certain number of devices with whatever type of interference are left on accidentally on every flight with thousands of flights a day and tens of thousands of devices "on", then:

1) We should have more problems with aircraft interference reports

Going back to this original question...

a) How do we know how many interference reports there really have been? This isn't info that average people would probably be privy to.

b) How would a pilot know that problems with an aircraft system were due to cell phone usage? If something's not working right, it's just not working right - a pilot probably isn't going to know the root cause of it unless he/she has lots of experience with this phenomenon. I would think that would generally be MX's job to figure out on the ground, but by then, the effects of the cell phone usage would be gone.
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Fly2HMO
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RE: No Man's Land On Mobile Interference?

Fri Oct 07, 2011 3:04 pm

Quoting spacecadet (Reply 26):

a) How do we know how many interference reports there really have been? This isn't info that average people would probably be privy to.

Easy: http://asrs.arc.nasa.gov/

There's hundreds of them there.

Quoting spacecadet (Reply 26):

b) How would a pilot know that problems with an aircraft system were due to cell phone usage?

Every time it has happened to me it was blatantly obvious. I had a total AHRS failure the instant I received a text/call on several occasions. It always happened during CAVOK conditions but had that happened duing an approach to minimums in bad weather at the very least I would have soiled my pants.
 
nomadd22
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RE: No Man's Land On Mobile Interference?

Fri Oct 07, 2011 3:42 pm

Quoting Fly2HMO (Reply 27):
Every time it has happened to me it was blatantly obvious. I had a total AHRS failure the instant I received a text/call on several occasions. It always happened during CAVOK conditions but had that happened duing an approach to minimums in bad weather at the very least I would have soiled my pants.


So, a potentially disasterous situation, the cause of which was obvious, and you kept doing the same thing that caused it?
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RE: No Man's Land On Mobile Interference?

Fri Oct 07, 2011 9:14 pm

Quoting nomadd22 (Reply 28):

So, a potentially disasterous situation, the cause of which was obvious, and you kept doing the same thing that caused it?

If I'm VFR I don't much care, since I'm looking outside anyways. PIC decision. And with the Garmin G1000 all you need to do to fix it is reset the system.

If IFR, or flying an airline, I ALWAYS turn it off.
 
XT6Wagon
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RE: No Man's Land On Mobile Interference?

Fri Oct 07, 2011 10:46 pm

If it was a real safety issue, why hasn't the FAA and the FCC gotten together and mandated cellphones have a system that when they recieve a coded pulse they disable all outgoing transmissions (other than 911). You could install two transmitters on each gate one at the bottom and one at the top. Bottom trips "airplane mode" and top releases it.

Simple, automatic, safe.
 
Fly2HMO
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RE: No Man's Land On Mobile Interference?

Fri Oct 07, 2011 11:34 pm

Quoting XT6Wagon (Reply 30):
If it was a real safety issue, why hasn't the FAA and the FCC gotten together and mandated cellphones have a system that when they recieve a coded pulse they disable all outgoing transmissions (other than 911). You could install two transmitters on each gate one at the bottom and one at the top. Bottom trips "airplane mode" and top releases it.

Simple, automatic, safe.

It is a great idea and I've thought of a similar system myself, but as always, nobody is willing to spend the money for it.
 
YokoTsuno
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RE: No Man's Land On Mobile Interference?

Sat Oct 08, 2011 1:53 am

Quoting tdscanuck (Reply 6):
There is a really wide gap between "interference that disrupts normal operation" and "interference that will kill you." Examples of 1) are legion, including multiple posters on this forum (myself included) who've experienced it firsthand. *However*, it's extremely rare for such interference to put the airplane in jeopardy.
That's how I see it as well.

Quoting Starlionblue (Reply 8):
There are other possible events that are way more likely to bring the plane down.
I have the same feeling. Why do people have an infatuation with cell phone interference while there are hundreds of other, far more risky, threats to bring an airplane down which nobody seems to care about? I guess the reason behind it is that people can't see radio waves and bestow them with “supernatural powers”. I guess this is why http://en.wikipedia.org/wiki/Maxwell's_equations  Good luck.

Quoting mandala499 (Reply 19):
Once you get closer to the ground, this changes! The phones can start latching on to ground cell towers... That's when the problem starts...
What problem does exactly start?
 
Quoting mandala499 (Reply 19):
the picocells are low powered for a reason...

Picocells are low power because they only need to cover the area of the airplane. Not to reduce interference. Since an airplane is small Picocell interference remains low as well.

Quoting mandala499 (Reply 19):
so that all the GSM transmissions between them and the phone can be done in low power too... therefore interference risk reduction

I am afraid this is not fully correct. As far as I know the only cell phone technology used in airplanes is basic GSM. A GSM-standard mobile phone always switches to maximum transmission power when it is setting up a link with a base station irrespective of the power of the base station. The reason is that the cell phone has no way of knowing how well its signal is received by the base station, so it assumes the worst case. It only starts to regulate (toning down) its power when it has negotiated the quality of the link.
This is BTW not to reduce interference but to save battery power.

Quote:
quote=tdscanuck,reply=16]the probabliity of an intereference event goes up by whatever factor left their devices on (probably a factor of between 10 and 100),

You triggered my curiosity here how levels of interference would increase if every passenger would switch his/her cell phone on. I had a heated debate with my buddies (RF engineers) at work last Friday. The ”consensus” was that the risk of interference would increase but not linear. Cell phones use complex modulation techniques like TDMA, CDMA, OFDM which makes this difficult to determine. The best way to explain this to a layman is that although it looks that the phone is transmitting and receiving all the time and on the same frequency in reality these devices often do the "skip and hop" and only transmit intermittently and on different frequencies. Even if signals coincide, the signal strengths do not necessarily add-up mathematically.
 
nomadd22
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RE: No Man's Land On Mobile Interference?

Sat Oct 08, 2011 2:13 am

Quoting YokoTsuno (Reply 32):
I am afraid this is not fully correct. As far as I know the only cell phone technology used in airplanes is basic GSM. A GSM-standard mobile phone always switches to maximum transmission power when it is setting up a link with a base station irrespective of the power of the base station. The reason is that the cell phone has no way of knowing how well its signal is received by the base station, so it assumes the worst case. It only starts to regulate (toning down) its power when it has negotiated the quality of the link.
This is BTW not to reduce interference but to save battery power.

That's not how it works. A GSM phone won't try to register or set up a link unless it receives a GSM signal from the base. And the strength of that signal determines the mobile unit's output power.
The thing that most people don't get is obvious once you think about it. The lower the base signal level the higher the power level of the mobile will be, since it interprets low incoming signals as meaning the base if farther away, which means the mobile needs higher output level to reach back to the base.
Meaning, a low powered pico-cell can mean high powered mobile transmissions.
Anon
 
Fly2HMO
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RE: No Man's Land On Mobile Interference?

Sat Oct 08, 2011 2:48 am

Quoting nomadd22 (Reply 33):
The lower the base signal level the higher the power level of the mobile will be, since it interprets low incoming signals as meaning the base if farther away, which means the mobile needs higher output level to reach back to the base.
Meaning, a low powered pico-cell can mean high powered mobile transmissions.

Exactly. CDMA phones do the same. Once airborne, a cell phone will barely get a signal from the towers and will increase the output to make up for that. It's to conserve battery power. There's no point in transmitting at 100% power if you're sitting right under a cell tower, cell phones only use what's necessary to keep a solid connection, no more.

Cell towers only radiate the signal horizontally (for the most part). And to make things worse, the airplane's fuselage acts like a Faraday cage, effectively bringing down the signal to zero, unless you put the cell phone right up the window, or you're sitting at the gate. So when you're airborne the cell phone is transmitting at full blast. Which granted is still not even that much power, but enough to cause glitches, however rare they may be. But that's not an excuse for pax to be condescending or disregard rules.
 
YokoTsuno
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RE: No Man's Land On Mobile Interference?

Sat Oct 08, 2011 3:52 am

Quoting nomadd22 (Reply 33):
That's not how it works.

Unfortunately that is how it works.

Although your theory is more or less correct (You forget to factor in receiver sensitivity, and fading which means that the Uplink and Downlink link budget are not always the same), in practice GSM cellular systems are far more advanced. It has a power regulating mechanism based on feedback irrespective of the transmitting power of the device. This works as follows.

The base station measures the signal quality (Bit Error Rate & Signal to Noise Ratio) and reports this to the cellphone. The cellphone then adjust itself (PCL or Power Control Levels). The cellphone also keeps a list of neighbouring stations with their respective quality figures of the links. The system compares these figures and decides if switching to another base station makes sense.

http://www.argospress.com/Resources/gsm/gsmpowcontro.htm
 
rwessel
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RE: No Man's Land On Mobile Interference?

Sat Oct 08, 2011 5:19 am

Quoting XT6Wagon (Reply 30):
If it was a real safety issue, why hasn't the FAA and the FCC gotten together and mandated cellphones have a system that when they recieve a coded pulse they disable all outgoing transmissions (other than 911). You could install two transmitters on each gate one at the bottom and one at the top. Bottom trips "airplane mode" and top releases it.

It would probably make a lot more sense to equip aircraft with RF detectors set up to detect the (limited number of) bands used by mobile devices. Make it portable so the FAs can search for an active phone, and then apply a real penalty to people who don't switch theirs off.

Such devices are available off the shelf for under $1K. For example:

http://www.cellbusters.com/product_info.php?cPath=21&products_id=28

(considerably cheaper units exist).

My position is that if cell phones are a meaningful threat to aircraft systems, failure to take reasonable and inexpensive precautions (like RF detectors), ought to make the manufacturers, airlines, and regulators criminally negligent should an accident happen.

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