<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by nfh:
I notice that American Airlines bans the use of GPS receivers on board. Does anyone know why? I've searched through the archive and although there has been discussion on this subject in the past, nobody has suggested why American Airlines should ban a harmless device that is passive and does not transmit.</font>
Well, actually they do to some degree. There has been a longstanding ban on operating an FM radio receiver or TV set onboard, and it's for the same reason. An FM radio receiver is also a transmitter to some small degree, due to the nature of how a superheterodyne receiver works (and virtually all FM receivers are superhets).
Although a single radio, TV, or GPS unit is unlikely to cause interference due to signal leakage, the worry is that a bunch of them might (or a single broken one). I think the need to ban these devices in-flight is a bit overcautious, but the underlying reason is not baseless.
By the way, WN specifially allows in-flight use of GPS by passengers.