I have a story about how it can be useful to have a cell phone on in an airplane. I was on my night x-c during my Private training, which turned into the biggest circus I ever hope to be involved in in aviation. I was flying with an instructor I never met until 1/2 hour before the flight, in an unfamiliar aircraft, doing unfamiliar things. Due to poor communication between student and instructor, we had three flight plans filed, one for each leg of the x-c, and one round robin. When I called Flight Service and asked them to open my FP, they did as I asked and opened the FP for the outbound leg. I got so distracted by all the unfamiliar tasks including using flight following, that it never occurred to me to question the need to close that flight plan or open one for the return, or why we had also filed a round robin. As we flew the return leg, the fact that people could reach the CFI on his cell phone didn’t prevent, but did limit and mitigate, the SAR response, and except for a great deal of embarrassment and a good butt chewing to a couple of pilots no one got in any trouble. Had they not called him, we’d have been “missing” for a good half hour longer than we were.

As to Steve’s point about the higher power levels from the towers: power levels for RF drop off with the square of the distance from the transmitter. Even if you fly right over a base station at say 200′ AGL, its signal has been attenuated 10,000 times more than the cell phone in the cockpit that’s only 2′ from the GPS receiver. The base station is only 50 times more powerful (100 watt max vs 2 watt max for a handset) so the received signal is substantially less from the base station.

The buzz from a GSM cellphone is due to the time division multiplexing scheme that turns the transmitter off and on 217 times a second. When operating at high power levels this creates large transient power draws on the battery and power subsystem that can generate significant interference in the audio band.

Can’t remember the details, but it seemed at the time to be a device with limited range.

One reason to turn cell phones off in flight is that the battery runs town constantly searching for new towers.

See you at AirVenture.

Next generation of aircraft/avionics may resolve this and then we can all be connected all the time.

One, and the most serious, occurred on short final at IAH in an MD-80 with the Wx at minimums. About the middle marker, the ILS CDI went ape with the CDI making major side to side excursions and causing the autopilot to disengage (coupled approach.) We initiated a go around. Probable cause was a cell phone activated in first class as witnessed by a flight attendant. After the cell phone was secured, the next approach was normal.

Both of the other problems were at altitude, above the magic ten thousand feet point where electronic devices may be used. In both cases the suspected culprit was a video camera being used in mid cabin causing wild, full scale deflections of the VOR CDI. Fluctuations ceased after the video camera was turned off.

When we drop to about 3000 AGL in urban areas we get a lot of signal from the cell towers (and they xmit more power than a cell phone). So why wouldn’t this issue be seen during approaches even without a cell phone being left on inside the plane?

This makes me wonder if this isn’t related to BlueTooth operations. It also has me wondering about processor clocking that is being transmitted when data needs to be processes into text (or something similar). Is this an intermediate freq Stage 1 problem (where a receiver transmits — this is the basis of how radar detector detectors work)?

It would be interesting to run tests for these things to find out what is really happening.

The only interference I’ve noticed was once when my former flight instructor decided to answer a call when I was practicing eights on pylons for my commercial…
Note, I used the word “former” flight instructor…