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Electronic Interference Part 2 – Computers and Games

Just as cell phones can cause interference with flight instruments, many other electronic devices can cause problems.Just as cell phones can cause interference with flight instruments, many other electronic devices can cause problems. Whether it is something as simple as an electronic game, or as complicated as a palmtop or laptop computer, all of these devices emit electromagnetic waves that can cause disruptions of the avionics and electronics used in your airplane.

WHAT’S GOING ON? Your avionics contain oscillators and crystals and these devices are used to generate frequencies, which in turn are used by the radio for proper tuning or to generate a signal to your various instruments. Each electronic device also generates similar frequencies -- along with harmonics, which are reflections of those frequencies at higher and lower points on the frequency scale.

PROBLEM — Many of the avionics used in aircraft today were designed before powerful laptops and palm sized computers were a reality. Although the manufacturers of avionics hardened their systems against the noise of other avionics of their day, they did not account for the explosion of technology and computers that currently exist.

DEFENSE — If you elect to use electronic equipment in your cabin while in flight...

  • Make frequent and full scans of your instruments -- including your wet compass.
  • Watch and listen for changes during power-up. When you first turn on electronic gear, look for changes in your course or instruments. Listen to the noise in your headsets as well.
Why: Non-electronic instruments such as the wet compass and the altimeter will help you to find course and altitude deviations before they can cause problems. Also, be aware that the noise from electronic games and computers can “bleed” into the headset and intercom system ... and cause you to miss ATC traffic!

BOTTOM LINE - Keep personal electronic devices away from your cockpit unless you are prepared to keep up a constant, vigilant scan of all of your instruments. If output noise or harmonic frequencies from your electronics coincide with the frequencies used by your avionics, the output of your avionics can be altered. If that happens to your autopilot and you don’t notice, you could end up in a very unpleasant place.

Editor’s note: For more in-depth reading on this and related topics, please see:
http://www.srg.caa.co.uk/news/Gsm_intf.PDF and
http://www.rvs.uni-bielefeld.de/publications/Reports/EMI.html

CASE STUDIES FROM BOEING
Flight crews of sophisticated jets, flying high above the ground have found interference with their navigation systems and various types of electronic equipment. Here are two examples of the problems they experienced:

Case #1
The crew of a commercial airliner noted problematic autopilot disconnects while in cruise flight. These disconnects were correlated with the use of a laptop computer in the aircraft’s cabin. The manufacturer of the aircraft bought the actual laptop from the passenger, and performed extensive testing that revealed that it exceeded various emission limits for use in the cockpit.

Case #2
In another case, a passenger’s palmtop computer was reported to cause a large commercial jetliner to initiate a shallow bank turn. One minute after turning the palmtop off, the airplane returned to 'on course.' When the palmtop computer was brought to the flight deck, the flight crew found that they could duplicate the problem by turning the palmtop on and off. Again, emission testing showed that the palmtop exceeded acceptable emission levels by up to 37 dB!

LESSONS

  • Use caution when flying with electronic gear -- whether in your own airplane or on a commercial airline. Also, when flying commercially,
  • Always abide by the airline’s instructions regarding the use of electronic equipment, and ...
  • Always comply with the requests of the flight crew.
Failure to comply with the flight crew’s request to secure electronic equipment, regardless of your training as an engineer, your experience as a pilot, or your beliefs of whether it will cause a problem or not can result in your arrest!

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