I suspect they included all reports for the time period in question which made any mention of PEDs, however peripherally. In any case, a controlled study is still a good idea. Although there are many reports of interference which apparently stopped after locating and turning off a PED which was powered on, one can’t automatically assume that the one was the result of the other; post hoc ergo propter hoc and all. As compelling as some of the reports are, a study to determine exactly what the nature of the interference is and how avionics are specifically affected is a good idea, if for no other reason than to improve the design of avionics to reject such interference.
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Those “reports” are certainly not a scientific test of interference.
I suspect the prohibitions against celphone use are a little like Pascal’s Wager. While a phone might not cause interference after all, keeping all of them off is the best way to never have a complication. After all, there might be just one device that hadn’t been tested and the potential for disaster is always there. Who wants to take even the slightest chance when lives are at stake?
Exactly. It is, at present, a theoretically mildly plausible risk with a small amount of anecdotal evidence behind it. Until a full study is complete to verify how much real risk there is, should we (a) allow passengers to use these devices, and hope that it won’t actually endanger all of their lives, or (b) subject the passengers to the mild inconvenience of not being in communication with those outside the plane for a few hours, just in case? Seems like a ‘duh’ question to me …
I could not agree more.
I’m thinking that a study is finally being implemented because airlines are wanting to introduce cell phone use as a “feature” of their service. The FAA and other authorities are probably a bit more interested in finding out exactly what is going on. Previously everyone was happy to ban the things on a just-in-case basis.
One of the problems with this issue is how to do a “scientific” test. Passenger electronic devices, like cell phones, are not perfect. They have spurious emissions, local oscillator radiation, harmonics, and emissions from digital circuits. They may or may not be properly shielded and filtered. Each type of aircraft has its own unique wiring and instrumentation. Shields on wiring may be damaged during maintenance or due to the effects of age. Put a random collection of transmitters, intentional or unintentional, in an aircraft at random locations in the passenger cabin, operating on random frequencies, with mixers provided by corroded metal-to-metal junctions, and who can predict the result? My experience with amateur radio has taught me that it can be difficult to reproduce and eliminate interference problems, especially when dealing with receiving weak signals in congested RF environments.
This is why I love the SDMB. I can be wrong, but understand why, and learn from it. I guess I can’t find a cite, since what I thought was basically wrong.
I think Musicat was spot on with the Pascal’s Wager theory, but more importantly with the explaination about tying up several towers. The cell phone companies most likely suffer most from people dialing from the air, compared to the FCC, the FAA, and the airlines.
Would it be feasible to build a small device, perhaps disguised as a cell phone, blackberry or laptop, that intentionally defeated the avionics on a commercial airliner?
If so, how effective might it be in causing a crash, say flying in instument conditions?
…in other news today, a Federal SWAT team arrested a certain A. R. Cane, on suspicion of attempting to manipulate information in order to force TSA to totally ban all personal electronics aboard airliners… 
I can’t imagine anything more annoying than trying to sleep on a redeye and being surrounded by travelling salesmen and turbo executives babbling on their bluetooth earpieces in 360° stereo.
While ruminating on just how a scientific test could be made, your post suggested someting. Why not try to make such a device as a test? If it did not work, that might give some confidence to the claim that ordinary consumer devices don’t interfere, either. But if it did, maybe it’s time for the airlines to do some hardening, cause it’s for sure that some terrorist will try it.
Is it? What is the range of a cell tower? At 41,000 feet they are what 8 miles up? In addition to that, how many towers can a phone that is 8 miles up “see”? I don’t know the answers to these questions, but I could see where Pygmy Rugger could be correct.
IANAP, but I’d expect that the FAA has some pretty stringent processes in place for every bit of radio transmission equipment that goes into an aircraft - under the “better safe than sorry” rule that I, for one, very much appreciate when I trust my mortal coil to an airliner.
I think the “no unauthorized transmitters” rule makes a heckuva lot of sense. It’s not really up to the FAA and/or the airlines to prove that cell phones are dangerous. It’s up to the forces (of darkness, IMHO) who want to use their cellphones that it’s safe. Undoubtedly, future aircraft will be designed around having live transmitters on the cellphone and Wi-Fi bands in the cabin, but most of the planes we’re flying were designed before anyone considered the possibility of every passenger carrying several two-way radios on their person.
Q.E.D.
Not quite incorrect, actually. There’s no real physical speed limit to roaming stations, but you do have to design your system around it. Moving a station from one cell to another stresses your central management systems who’ll need to reroute traffic. The faster a staion moves, the more often it’ll change cells. Add to that the problems involved in a station being airborne, with line-of-sight to more towers than a station on the surface, and you’re really adding to the load. That the system handled the 9/11 calls does not mean that it would be able tackle tens of thousands of calls under the same conditions.
Yes, but this is really a function of how long it takes for the signal to change strength in between stations. If the planes were flying overhead at 200 feet, it would be an issue, but at 35,000 the signal strength changes very slowly from one cell to the next. This is clear if you think about how small the angle subtended by a plane at 35,000 feet in a given timespan compared to that at 200 feet in the same amount of time. In other words, the relative angular velocity is much more important than the linear velocity.
I should add if you mean the number of cells that are involved in handoffs during a given period of time, then I agree with you. Again, though, that’s more a function of altitude than velocity.
I believe they used those pay phones, which use - IIRC - satellite systems. I know at least one did as the operator who handled the call has had a number of interviews on TV.
Digital cell towers have a hard range limit of ~15 miles, due to timing requirements. If the airliner is 6 miles up (~30,000’) then the radius of the coverage area at that altitude is 13.75 miles. If it passes over the cell tower, then it will be in range for the maximum distance of 27.5 miles. An airliner traveling at 650 mph will cover that distance in 2 minutes, 32 seconds. This time will decrease considerably if the airplane doesn’t overfly the cell site, or is it higher altitude, as it will only “clip” the coverage area.
Cell systems are configured with considerable overlap in coverage of the cells, so a reasonable guess is that the handset would be switching cells every 30-60 seconds.
I have no idea what overhead this imposes on the infrastructure.
As an instrument pilot I would be very upset if a passenger used a electronic device that just made a little static in my head set at just the wrong time. He does not need to mess up the navigation, just make the pilot miss something important and everybody loses.
According to the logs, both conventional celphones and Airphones were used, and operators often didn’t distinguish. I’m sure they had more important things to do than ask a caller what brand of phone he was using.
If this were GQ, I’d find a link to the logs, but since it isn’t, you’re on your own. I ran across several when I was reading this thread last week, so they shouldn’t be that hard to find.