I did both the FCC and FAA submittals for the system that Qualcomm did the front end system design for. It was one of the more interesting systems I have ever worked on because of the blend of commercial avionics and consumer electronics. Let me clarify a few issues.
Airborne cellar shares the same band (NOT the same frequencies) as the ground based cell systems. However, the transmitter power levels were around 25 watts making the system substantially more powerful than a ground type mobil cell phone. Therefore if there was no EMI to the aircraft systems (several octaves lower in frequency) from the airborne cell system, then it is highly unlikely the lower powered ground cell phones would cause any interference to the aircraft systems either. It was never a concern to the FAA. So why not allow ground based cell phone usage while in the air? The answer is ground based systems rely on FM radio's capture characteristic to allow very heavy frequency reuse. The low powered ground units depend on the mobil unit seeing only a few cell sites so they can reuse the same frequencies at other cell sites. The system measures the power level at the individual cell site and determines which antennae (and cell site) to use. If the power levels are saturating at more than one cell site, (as is typical when the aircraft can see many cell sites) the system can not determine which antenna to use and locks up. There are issues too. Cell sites are designed for slow moving mobiles where there is plenty of time to anticipate of the hand off to another cell site. Airborne units quickly overtake a cell sites causing existing mobil connections to be dropped. One airborne mobile cell phone can wipe out many ground mobile cell sites. So the real answer to the question of airborne mobile cell phone usage is not interference to the aircraft or aircraft navigation system; rather it is interference of ground based mobile units. Fred Townsend Brent DeWitt wrote: > It's conceivable, but the folks at Qualcomm I did base station testing for > seemed to think the problem was real, and they don't make aircraft systems. > > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf > Of [email protected] > Sent: Thursday, January 25, 2001 10:26 AM > To: [email protected] > Subject: RE: consumer electronics used on board aircraft > > I may regret saying this, but isn't it conceivable that the FCC Rules that > make it illegal to use a cell phone in the air has more to do with the right > of the airline to sell expensive phone time, than the technical issues? :( > > -----Original Message----- > From: Brent DeWitt [mailto:[email protected]] > Sent: Thursday, January 25, 2001 10:08 AM > To: Mike Hopkins; 'Colgan, Chris'; 'Emc-Pstc' (E-mail) > Subject: RE: consumer electronics used on board aircraft > > My background is the pretty much the same as Mike's, which is probably why I > agree with his response. I just wanted to add that the prohibition on cell > phone usage (in the US at least) is not FAA or airline driven, but mandated > by the FCC. The architecture of the cellular system is rather carefully > planned. The placement of antenna sites, coverage and hand-off algorithms > are based on the propagation from land based phones, which is quite > different from a phone in an airliner 25000' feet up. The FCC has therefore > made it illegal to operate a cell phone after the wheels of the plane leave > the ground. > > Regards, > > Brent DeWitt > > "Takeoffs are optional. Landings are mandatory" > > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf > Of Mike Hopkins > Sent: Wednesday, January 24, 2001 11:38 AM > To: 'Colgan, Chris'; 'Emc-Pstc' (E-mail) > Subject: RE: consumer electronics used on board aircraft > > As a frequent flyer and private pilot with some knowledge of EMC, I'll throw > in a few comments: > > It is clear to me that consumer electronics can interfere with aircraft > electronics, and I've probably heard all the same horror stories -- DC10 > finds itself off course on landing, false engine warnings, interrupted > communications, etc... It isn't clear to me how prevalent this problem is or > if it happens often enough to be considered a problem. One instance of > electronic interference is enough to have everyone up in arms against the > use of ANY electronics in ANY airplane. > > On a 747 flight to the Pacific, I'd bet there are as many as 30 to 40 lap > top computers operating together at some point during the flight. > Additionally, there are probably another 40 to 50 walkman tape players or CD > players in operation, plus the on-board entertainment systems and a few > in-flight telephones being used. On shorter flights, there may still be a > large number of laptops being used by business people plus tape/CD players > and air phones and the like in use during the flight. I don't think this is > a general problems for aircraft electronics. > > HOWEVER; if radio or television receivers or cell phones were allowed, I > believe the level of interference could easily reach the level of being at > least disruptive to aircraft systems if not downright dangerous. I have > personally seen commercial scanners and FM broadcast receivers that will > interfere with voice comms -- 118MHz to 136MHz -- which means they could > certainly interfere with nav equipment operating between 108MHz and 118MHz > (VOR's and ILS's, specifically). I also have a Garmin hand held GPS system > that I cannot find anything that it will interfere with nor have I found > anything that interferes with it (except things getting in the way of the > antenna - Maybe I'm just lucky?). > > My sense is the following: Interference with nav stuff is the most likely -- > a VOR indicator off, or something like that. With GPS back-up (or getting to > be primary) in most aircraft, a faulty Nav indication would likely be caught > before it was a problem (NOT so if you're on an ILS approach in IMC > (Instrument meteorological conditions) where a faulty indication can run you > into terrain -- this is why no electronics should be operated on the > aircraft below 10,000 feet on take-off or approach). > > I doubt a cell phone caused the Saab to crash -- most airplanes will still > fly even with all electronics blocked out (don't know if the Saab is fly by > wire or not, but I don't think so). Horizontal situation indicators and > gyro's are driven by vacuum and in larger airplanes, there's back-up vacuum, > red flashlights in the cockpit, etc... Upsetting autopilot controls might > cause the airplane to do something erratic, but that sort of thing should be > recoverable as long as someone in the cockpit is paying attention. > > Enough of that -- need to get back to my real job.... > > Mike Hopkins > KeyTek > > -----Original Message----- > From: Colgan, Chris [mailto:[email protected]] > Sent: Wednesday, January 24, 2001 6:15 AM > To: 'Emc-Pstc' (E-mail) > Subject: consumer electronics used on board aircraft > > There is growing concern amongst professional aircrew about the use of > consumer electronics (CD players, mobile phones, hand held GPS etc) on board > aircraft. Some claim that passenger electronics has definitely interfered > with navigation systems, primary flight displays or engine warning systems. > There are rumours that a mobile phone contributed to the demise of a > Crossair Saab 340 on 10 Jan 2000 killing all passengers and crew. Some > pilots reckon that it is absolute nonsense. > > Knowing what you do, about how EM disturbance can affect electronics > equipment, that it is almost impossible to make electronics equipment > completely immune to EM effects, that FCC class B or CE marked equipment has > not been tested (presumably) with avionics in mind etc, etc, how do you feel > when the guy next to you on your flight gets his Minidisc player or laptop > out? Remember, when you are descending through a cloud layer, the pilot is > relying solely on electronics receiving equipment to get the aircraft on the > runway. > > Do you think all consumer electronics should be banned from aircraft, that > FCC or CE equipment is okay or that the whole issue is scaremongering > piffle. > > Any comments gratefully received, I will post a summary on a professional > pilots forum and let you know that results. > > Regards > > Chris Colgan > Compliance Engineer > TAG McLaren Audio Ltd > The Summit, Latham Road > Huntingdon, Cambs, PE29 6ZU > *Tel: +44 (0)1480 415 627 > *Fax: +44 (0)1480 52159 > * Mailto:[email protected] > * http://www.tagmclarenaudio.com > > ************************************************************** > Please visit us at www.tagmclarenaudio.com > ************************************************************** > > The contents of this E-mail are confidential and for the exclusive > use of the intended recipient. If you receive this E-mail in error, > please delete it from your system immediately and notify us either > by E-mail, telephone or fax. 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