A series of tests conducted in conjunction with Vodafone exposed a set of aircraft avionic systems to simulated mobile phone transmissions.
They revealed various adverse effects on the equipment's performance.
Although the equipment allowed a margin above the "original certification criteria for interference susceptibility", the margin was not sufficient to protect against potential mobile phone interference under worst-case conditions, the authority said.
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The study could be a blow to some airlines, such as Scandinavian Airlines System (SAS), which hoped to offer passengers the opportunity to use their mobile phones in the air as they do on the ground.
Mobile phone use has long been banned on flights, while the use of many other electrical devices, such as notebook computers, are banned on take-off and final approach.
But passengers, particularly business people, are interested in using their phones on planes to keep in touch with their offices and customers.
In the US, the Federal Aviation Administration (FAA) bans the use of mobile phones on flights because, like the CAA, it too is concerned about wireless calls interfering with a plane's navigation system.
From March 1996 to December 2002, CAA recorded 35 aircraft safety-related incidents that were linked to mobile phones.
The reported interference incidents included interrupted communications because of noise in the flight crew's headphones.
CAA recommends a continued ban on mobile phone use by passengers in aircraft and urges airlines to introduce safety procedures that ensure phones are switched off.
Whether the CAA study will encourage airlines to prohibit the use of mobile phones with flight-safe features remains to be seen.
Last week, SAS announced a policy for allowing passengers to use all mobile phone functions, such as calendars, address books and reading e-mail, that require no signal transmission.
To do so, passengers would require phones equipped with a flight-safe mode, which prevents a handset from sending or receiving signals required to make phone calls.
Nokia's 9210i Communicator and Sony Ericsson's P800 smart phone are among the first handsets with the flight-safe feature.
"We continue to recommend to our customers that they should turn off their mobile phones when inside aircraft and should only turn them back on if equipped with the flight-safe mode," said Nokia spokesman Damian Stathonikos. "But we understand that some airlines prefer passengers not to use their mobile phones at all."