Altitude reception

[Admin]

I found something very interesting on my commercial flight last night traveling from Melbourne to Brisbane. I had forgotten to switch my Samsung tablet over to flight mode and proceeded to play solitaire to kill time. We were traveling at 39,000 feet and I started receiving emails and had full Internet connection and no, I wasn't using Virgin Wi Fi, just my Telstra normal sim card connection.

 

I quickly switched on flight mode to make the powers to be happy but I thought that it was quite extraordinary to get a connection at such a high altitude.

 

 

[dutchroll]

It is very unusual to get a mobile signal at commercial cruise altitudes, but possible.

 

My ATP colleagues and I have, while at work, *cough* occasionally been known to accidentally leave our mobile phone or iPad on in its normal mode (we are supposed to go to switch off mobiles before departure like everyone else, with the exception of iPads which remain on in flight mode). What usually happens with this omission is that you get nothing until shortly after touchdown and it starts beeping with messages and missed calls you've had while flying, leading to an inevitable wisecrack from the guy in the other pilot seat: "someone left their phone on did they?" However I have seen an iPad pickup a 3G signal then download email on a couple of occasions at cruise altitude!

 

(Truth be known, there is actually no concrete, verifiable evidence at all that a mobile phone or iPad can interfere with the navigation or flight control systems on a modern commercial jet and a reasonable amount of evidence that they don't, but the FAA position has always been that they require "proof beyond any doubt" that they cannot ever interfere with any system, which is a burden of proof virtually impossible to achieve.)

 

 

[Head in the clouds]

(Truth be known, there is actually no concrete, verifiable evidence at all that a mobile phone or iPad can interfere with the navigation or flight control systems on a modern commercial jet and a reasonable amount of evidence that they don't, but the FAA position has always been that they require "proof beyond any doubt" that they cannot ever interfere with any system, which is a burden of proof virtually impossible to achieve.)

Interesting. When Optus was first setting up in the Top End I knew the Head Honcho pretty well on a social basis and he said that the whole 'interfering with the navigation system' thing was a load of old (shoe repairers) and that in fact, with the advent of the cell phone, a deal had had to be done between the FAI/CAA etc and the various national governments to introduce legislation making it illegal to use mobile (cell) phones whilst airborne because if everyone who was airborne all had their phones turned on the phones would each log on to multiple towers because many would be 'visible' from the air, and overload the system.

 

I don't know how the cell system works and if that was the case or still is but I don't have any reason to doubt the source. What I do know is that many countries (Eastern Europe, parts of Asia, TPLACs (tin-pot little African countries, Yes Minister)) either don't mention turning off phones and/or don't enforce it and they don't seem to have any navigation or other systems issues ...

 

 

[dutchroll]

Yeah I'm not so sure the "log on to multiple towers and overload the system" argument is valid anymore in the modern digital network era, however the FAA "burden of proof" obstacle remains for mobile device transmissions in aircraft, and it's just easier and cheaper for airlines to say "don't do it".

 

It does pain me to listen to our own flight attendants doing the PA stating that mobile devices interfere with navigation systems. It's simply not even remotely conceivable that a mobile phone will interfere with an Inertial Reference System any more than a normal regular VHF or HF com transmission would, but they're just reading from a company/CASA script as they're required to do......and them's the rules.

 

 

[Guest Andys@coffs]

The cell issue was related back to gsm or 2nd generation technology. The cells were electrically limited to be small in size and there was a whole login to cell, followed by handoff to next cell. At cruising altitudes you are already approaching the cell limit in terms of distance from cell so there is significant protocol traffic as the phone and cells below look for a workable solution where there really isn't one. It's why 2g phones that were good for a day went flat real fast if you didn't switch them off before flying.

 

For 3G and 4g there is only the practical length associated with can the receiver still get line of sight to the cell. At cruise altitudes due curvature of earth you can have a significant number of cells that can be seen by your phone and which don't appear from the cell perspective to be straight up and therefore out of the base station radiation pattern. It's why 4g tracking apps work really well at greater than 3000ft but may well stop working soon after on descent as curvature of the earth takes a bunch of cells out of line of sight. Same reason the PCA has different coverage patterns for the ATC freq's depending on VFR cruising alts.

 

Inside the cockpit of a bigass Boeing or Airbus however there is a heap of metal between the cell and the tower, even the windows may well have a metalised coating..... Flying a jabby is almost the same as having no metal shielding to a mobile....but I do find it difficult to test your altitudes duchy lest casa do a job on me assuming I didn't become a radome adornment first......

 

Andy

 

 

[Ferris]

I am going off in a bit of a tangent here, but I vaguely recall reading an article suggesting that while mobile phones are not a problem to navigation, but FM radios can be. I've looked for the article and can't find it, but I have a recollection that the frequency modulator within the receiver can affect VORs. Does anybody know if this is correct, or have I been out with the fairies. Cheers Ferris