Interference from Row 9

July 19, 2012 by Bruce Landsberg

I’ve been somewhat skeptical about electronic device interference with avionics, but a recent ASRS (NASA report) shows there may be some credibility to at least securing cellphones while airborne.

A CRJ flying at 9,000’ received an EFIS COMP MON caution message:

“Flight Manual directs pilots to slew compass to reliable side. It was apparent neither side was correct with the Captain’s, Mag Compass, and First Officer’s headings all different. We were cleared direct to a fix. Multiple attempts were made to match the headings with only temporary results. The Captain elected to hand fly while the headings mismatched. While the FMS was taking us in a direct line, with the wind shift while hand flying the aircraft ended up 4 miles south of the original ‘direct to’ course. ATC called and asked if we were going direct, I told them we are having heading problems and asked how our heading looked. He told us 10 right and direct when able. On this trip we flew this same aircraft for 9 legs and did not have this problem on any other flight. In the past I have had similar events with speculation that cellphones left on may contribute to the heading problems.

The first Officer made a PA announcement asking everyone to check their cellphones and the flight attendant walked through the cabin. Sure enough, in Row 9 was a phone in standby mode—not airplane mode. The passenger said he didn’t know how to program that so the flight attendant showed him and as soon as the phone was secured, all the avionics worked perfectly.”

I’ve spent a fair amount of time on GA aircraft where there were laptops open on board, and of course iPads/tablets, with no problems. Of course if it’s in the cockpit, one had better be dividing attention appropriately—that means not near any airports while VMC, and listening up for ATC calls. We might remember some pilots who missed the destination by a few hundred miles while fooling with a laptop. But that interference was mental, not electronic.

I’ve been on GA flights with passengers whose phones were most surely not secured, and there have been no anomalies. However, it probably just means all the links in the electronic accident chain weren’t quite in alignment. As we learn more about the hardware and its interference profile, there’s the opportunity to either provide better shielding, or just shut the blooming thing off!

We did manage to live reasonably full lives before the cell phone, although the Twitterati might dispute that. Let me put it this way—being momentarily out of contact beats whacking the ground because the nav instruments were confused by phone jabber. Has anybody else had a problem with electronic device interference?



Bruce Landsberg
Senior Safety Advisor, Air Safety Institute

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  • Brian Turrisi

    Have had phone interference on two different dates. One resulted in the GPS satellites not being received correctly on a Garmin 430. The antenna for this satellite was only 18 inches from the phone. Resolved with switching it off.
    The other was COM radio interference that also stopped when the phone was turned off.

  • Fred von Zabern

    It seems like phones left on will invariably interfere with the com audio with an annoying buzz… buzz… buzz… buzz… buzz… sometimes to the point where it will block the com receiver’s audio output to headsets or speaker.

    I ask people to turn their cellphones to “airplane” mode, which prevents this, and tell them that doing so preserves their phone battery charge. Apparently the phone, if left on in flight, searches for cells, which consumes battery power. Pax seem to like the idea of conserving battery power, even if they’re skeptical of the “myth” that their phone interferes with avionics.

  • Karl Schneider

    About 15 years ago when I was flight engineer on the 727 for a major airline we had both our compass systems drift off twice during one flight. After the flight a flight attendant told us that twice during the flight she’d had to stop a passenger talking on his cell phone.

  • Andy Young

    I have had the same experiences as Fred (above) I fly for a 135 air taxi in Alaska. There is no cell service near our base, but when flying to areas that have service, we often get the annoying buzzing as we get close, as soon as any phone left on starts picking up a signal and recieving messages/texts that have been backing up while the phone owners were in the backcountry. Invariably, the offending phone is buried in the baggage area, and cannot be accessed until we land.

  • Bonanza Babe

    “Has anybody else had a problem with electronic device interference?”…

    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…

  • Steve.T

    I have a few questions (I used to work with commercial radio systems):

    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.

  • Chas

    Three instances.

    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.

  • Bruce Landsberg

    Thank you all. I believe my last two paragraphs sums it up and for the time being, we would all be well served to ask passengers to secure cell phones particularly in IMC.

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

  • Joe Tannehill

    I am an electromagnetic compatibility (EMC) engineer. This is the discipline of testing and designing electronic devices to 1) Not cause interference, 2) Not be susceptible to interference. Each industry has its own standards to comply with as well as the FCC requires it by law. That means that the hand held devices must comply with FCC part 15 in the states and EN 55022 and EN 55024 outside of the US. Aircraft meet RTCA DO-160. I threw those in for reference. That said electronic devices can be non-compliant through manufacturing issues, improper testing, or design. Sometimes a mechanical shock (drop) can shift grounding or shielding devices that make them non compliant. Further, there is possibility that even if all is correct there is no guarantee that it will not interfere. It is just due diligence that we depend on. The buzz – buzz – buzz that you hear is from the AM modulation scheme that is used in some (older CDMA) phones. However what is happening is that the phone transmitter has found a cable or circuit that is resonant to that frequency and AM type modulation is heard in the audio circuits. I used to use the old ‘blender interfering with TV’ scenario to describe what I do. Now I use the buzz – buzz. I tried to be brief but I could go on. Bottom line is that by design it should not interfere, but it can under several circumstances. Garmin, Apple, Dell, IBM….All test for this.

  • Martin Sobel

    I’ve seen interference many years ago on a DC-9 flight between STL and CMH.

    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.

  • Frank

    I’ve had a couple of instances where a GNS530W lost all satellites, then recovered as soon as all iPhones in the plane were switched to airplane mode. This happened in a PA-28 where the GPS antenna is only a foot or two from the phones in the cabin.

    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.

  • Mark C

    Joe Tannehill, thanks for the insight, that’s interesting. It would have been useful if the flight crew in the CRJ had made note of the make, model, and service provider of the phone which caused the problem. With actual data engineers and others could possibly solve these issues and make everyone happy and safe.

    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.

  • Randall Henderson

    In my RV-6 I added an XM portable music receiver, plugged into my PM2000 intercom’s music input. Immediately I noticed reception problems on my Garmin 396. I played around and it was very repeatable, and I could see all of the satellite bars drop by 25% to 50% with the XM music receiver on. The device was normally about 2 feet from the GPS antenna. If I separated them by 4 feet the effect went away. This is closer proximity than is likely between an airliner antenna and passenger seat, but still.