CATHAY Pacific has joined a growing number of carriers around the world either limiting or banning passenger-owned electronic equipment from its aircraft. Although it has not been proven conclusively, evidence is starting to emerge that electronic equipment such as lap-top computers and portable phones may have a serious effect on aircraft flight-management computers and navigation systems. A spokeswoman for Cathay Pacific said: ''Although the Federal Aviation Administration in the United States has said there is no cause for concern our primary concern is passenger safety. ''We are now advising passengers that the use of portable telephones, compact-disc players, walkie-talkies and CB radios will be prohibited at all times on the aircraft.'' The International Air Transport Association's (IATA) Safety Committee recently produced a report highlighting some of the problems. According to a report in Flight International : ''Problems have been experienced on a wide range of aircraft types, including the McDonnell Douglas MD-80 and DC-10, Boeing 727 and Airbus A320.'' Meanwhile, IATA has recommended that ''no passenger-operated electronic device should be operated in the passenger cabin during take-off, climb to initial cruise altitude, or during descent'' until the problem has been sorted out. Some of the problems, according to the magazine, have included: Douglas DC-10: automatic-direction-finder (ADF) bearing discrepancies. Two Nintendo Gameboy computer games were being used. When they were switched off, the problem disappeared; Boeing 747-400: aircraft started oscillating left and right of track during flight. When the captain visited the cabin he noted two passengers operating lap-top computers. When the machines were switched off the oscillation stopped.