Its hard to believe that anyone who has flown a plane much has not heard the interference of a cellphone handshake (repeated creaking sound) over the RT or intercom.
It is equally hard to believe that anyone with enough technical knowledge to fly an aeroplane cannot understand that if the RF from a phone can induce a signal like that in a comms system it can do the same in any other electronic system - eg a control system.

As said above, there need to be too many 100% protection levels in too many different aspects of systems to assume immunity, and we cannot possibly predict how a signal from a mobile device in an infinite number of positions and orientations might be reflected and concentrated by structures and fittings into a vulnerable spot.

So is medical equipment but it happens, and one potentially extremely serious malfunction was witnessed first hand by one of our very experienced technicians.

Hello I’m new here!

I wouldn’t normally venture into Tech Log because I bimble around in a rented 152. My day job in designing and deploying mobile networks, including a couple of onboard cells used in many wide bodies.

Mobile phones adjust their transmission power dynamically depending on how far away they are from the nearest base station(s). At an airport their power will be very low because there’s several BS’s in the terminal. As they get further away the need to up the power.

Smart phones especially are in continuous communication with the network even when they are not being used. Push email, weather apps, facebook, Tw!tter and the like exchange data on an almost continuous basis.

A Smart phone is trying to keep two radio streams open, one for the voice and sms service and another for data. A mobile onboard an aircraft quickly gets confused. It finds itself moving too fast to be a able to locate and handover to another base station successfully and gets into a panic. As the distance between phone and ground increases so will the transmission power. It’s also struggling with the data connection. In normal operation the phone will use the fastest data service available which is normally HSPA or 4G, as the signal degrades it will fall back onto slower technologies with better reach; UMTS, then EDGE, then GPRS. In the air this signal degradation happens a lot faster due to the vs and forward speed. This also stresses the phone as it hurriedly tries to switch to slower technologies. Bursting data, renegotiating, bursting data again etc.

Once out of range of the base stations it will periodically search for a connection, sometimes at maximum power. Also, don’t forget the communications that might be going on with the PAX’s other technology. Bluetooth headsets, tethering and portable WiFi hotspots could all be exchanging information with each other.

The point on the previous page about airlines being RF immune is not correct. For starters they use RF to communicate! Although everything should be shielded perfectly that changes with age and maintenance interventions. Degraded insulation, temperature changes, stretch and flex will all open an aircraft up to potential interference. I know of a case, unfortunately not documented or scientifically proven in which a mobile was firmly blamed for slowing down the clock speed of a FADEC on a Williams FJ44 by a few MHz. Having a base station onboard will actually significantly reduce the chances of interference as the transmission power needed to communicate a few metres is very small. There’s also no cellular handover on onboard systems meaning phones don’t search around for other base stations.

flight_mode:Assuming this is true (as you say, not documented...), there seems to be a very low level of EMI protection on said FADEC. How could it survive a lightning strike - or (in a military world) a nuclear EMP?

Just as a oh-by-the-way. Screening a cable does not protect much against some types of interference. Electrical energy is carried by fields with a voltage component and a magnetic field component. Screening doesn't protect much against the magnetic component and, depending on the local impedance of space, the magnetic component can carry a lot of the energy.

With most information these days being moved in the digital domain, it is easy to produce a signal that has never been produced before. This makes testing very difficult.

After an excellent landing...

Probably the next step since some passengers don't shut off their cell phones is a flight attendant to walk down the aisle with a signal detector to catch the ones that don't comply with regulations.

As a pilot of a B757 I was amused by my cell phone going off at 3,000 ft on approach because I forgot to turn my captain cellphone off. It never caused a problem. It just said I missed a message. I didn't mean to do it, just forgot. I always stayed in tune with my wet compass so never let my heading change due to RF interference. With satellite nav with a minimal skill on using the wet compass no airliner should ever have a navigation problem. I practiced it all the time in my 757 heading south out of MIA.

We still have the magenta line followers that might have a problem. Not much we can do with them, I guess. I did the whiskey compass because I started in an Aeronca Champ and that is all I had. The B757 compass works the same way. The basics will always get you through, the Magenta line may if it is programed properly.

I once read that the true reason mobiles are banned, is due to the mobile carriers overload when the phones are in flight and and have tooo many antennas in line of sight.

My career missed that part. What airline cares if Verizon has overloaded cell stations on the ground? I know AA didn't.

It's also fiction. A mobile phone only access one tower at a time no matter how high they are.

Not the airlines but the FCC slash government slash FAA

Note that some systems can make use of more than one base station simultaneously:

"Since adjacent cells use the same frequencies, CDMA systems have the ability to perform soft hand offs. Soft hand offs allow the mobile telephone to communicate simultaneously with two or more cells. The best signal quality is selected until the hand off is complete."

Source: https://en.wikipedia.org/wiki/Code_d...ultiple_access

Ah yes sorry, soylentgreen, that's pretty much for the hand-over between the cells. So yes a mobile phone will talk to two towers at once, but it's really only working with one at a time.

I cannot comment on the CRJ issue since i'm not familiar with the type but i had my phone accidentally on throughout the flight at least 5 times in the last 10 years (A320/A330/A340) without any nav problem and also in my current outfit we have gsm/3g data/wifi enabled above 20.000ft and no fault was ever spotted. (Long haul, widebody operation, A330/A340)

One should be aware that poor electrical interconnections have non-linear properties that can result in the production of anomalous sum and difference frequencies that are usually quite unpredictable.