Cell phones on planes

December 14, 2005 - Reading time: 5 minutes

It seems that people are skeptical about the dangers of operating Portable Electronic Devices (PEDs) on airplanes.  I've heard the same tired argument ("but I leave my phone on all the time, nothing bad happens") several times already.  Well, sometimes bad things do happen.  Usually not "planes dropping out of the sky" bad, but bad nonetheless.  Airplane systems (including Air Phones and the like) are subject to rigorous electromagnetic emission standards to establish and provide control of the electromagnetic characteristics and compatibility of these systems.  PEDs, however, are not subject to these restrictions, and electromagnetic interference from PEDs carried on by passengers have been reported as being responsible for many anomalous events during flight.  Some examples, provided by Boeing:

  • 1995, Boeing 737: A passenger laptop computer was reported to cause autopilot disconnects during a flight.  Boeing purchased the computer from the passenger and performed lab tests on the device to see its electromagnetic emissions.  The emissions exceeded the Boeing emission standard limits for airplane equipment at several frequency ranges.
  • 1996/1997, Boeing 767: Over a period of eight months, Boeing received five reports on interference with various navigation equipment (including uncommanded rolls, pilot displays blanking, flight management computer/autopilot/standby altimeter inoperative, and autopilot disconnects) caused by passenger operation of a popular handheld electronic game device.  In one of these cases, the flight crew confirmed the interference by turning the unit on and off to observe the correlation.
  • 1998, Boeing 747: A passenger's palmtop computer was reported to cause the airplane to initiate a shallow bank turn.  One minute after turning the PED off, the airplane returned to "on course."  When the unit was brought to the flight deck, the flight crew noticed a strong correlation by turning the unit back on and watching the anomaly return, then turning the unit off and watching the anomaly stop.  Boeing was not able to purchase the actual PED, but contacted the PED manufacturer and purchased the same model.  Boeing laboratory emission testing revealed that the unit exceeded Boeing airplane equipment emission levels by up to 37dB in several frequency ranges.

In another widely known incident, in January 2001 a Slovenian airliner made an emergency landing after a passenger's mobile phone caused its electronics system to malfunction and indicate there was a fire on board.  The plane was a Canadair Regional Jet CRJ-600, a modern and sophisticated aircraft.  In another incident, the pilot's mobile phone was identified as the source of interference causing a loss of GPS guidance on three separate GPS receivers during a Piper Cherokee test flight.  USAirways has reported that interference from cell phones used during taxi-in caused the emergency lighting system to activate on one flight.

PEDs have been implicated in interference with many aircraft navigation, flight control, and safety systems: the VOR (VHF Omni-directional Range), LOC (Localizer), CDI (Course Deviation Indicator), Autopilot, pilot displays, FMS (Flight Management System), TCAS (Traffic alert and Collision Avoidance System), radio communications, radar altimeter, IRU (Inertial Reference Unit), ILS (Instrument Landing System), smoke/fire detectors, and aircraft spoilers, among others.  Laptops and cell phones have been the biggest offenders, with handheld game devices and portable TV/DVD players close behind.  Boeing also conducted laboratory and airplane tests with 16 cell phones typical of those carried by passengers; the results indicated that phones not only produce emissions at their operating frequencies, but also produce other emissions that fall within airplane communication and navigation frequency bands (such as the Automatic Direction Finder, High Frequency, Very High Frequency [VHF] omni range/locator, and VHF communications and the Instrument Landing System [ILS]).  Emissions at the operating frequency were as high as 60dB over the airplane equipment emission limits.

It's not just PEDs, either.  In early production runs of a particular Lear Jet, the Radio Direction Finder (RDF) would peg to one side if the window defroster was used, because the little defrosting wires on the glass were right next to the RDF instrument.  Were a pilot to follow the RDF when the defroster was switched on, he or she would be flying in a tight circle.  This is an extreme example, but more minor examples exist.  Interference could cause just enough of a change in an automated system that people wouldn't notice a change in direction but the pilot could land at the wrong airport by accident (this actually happens quite frequently).

Is it possible that electromagnetic interference could bring down an airplane?  Yes.  A seven month study by the US Air Force completed in late 1998 concluded that "thousands of conflicts" among radio frequencies used by the three branches of the US military had produced grave outcomes.  According to Colonel Charles Quisenberry, the director of the study, EMI can "affect the electrons within the aircraft's flight controls as well as its fuel controls ... putting a plane into an uncommanded turn or dive or turning off its fuel supply."  Some forms of interference, he stated, "are very, very critical -- some cause aircraft to crash."  He gave some instances where this was the case: because of EMI, Black Hawk helicopters crashed and killed their crews five times between 1982 and 1988, with 22 deaths.  "The Black Hawk was shielded at a very low level -- it was known ahead of time that its shielding was inadequate."  One Army aviator had gone on public record saying that "EMI is causing these aircraft to flip upside down and crash and kill everybody aboard."

Lots of electronic devices put out RF interference in unpredictable ways, and more and more devices come out all the time that are small and light enough to carry on to the plane.  The FAA has banned the use of all electronic devices during takeoff and landing because of this uncertainty.  Because of strong contrary public opinion, PEDs have not been banned outright on flights, but given the uncertainty, it is probably safest to switch them off as soon as the boarding door closes, and leave them off until the door has opened.