(CNN) -- Just when you thought it was safe to switch on your cell phone, it seems that making calls in the air could pose a greater risk than running up an exorbitant bill.
A new study by scientists at the Carnegie Mellon University shows that interference caused by mobile phones may create more interference to aircraft navigation systems than previously thought.
If true, the findings -- which also reveal that many passengers are flouting current in-flight cell phone bans -- could call into question airline plans to wire jets to accommodate mobile networks.
The Carnegie study, carried out with support from the U.S. Federal Aviation Administration, showed that phones and other portable electronic devices such as laptops or games consoles can interfere with critical aircraft electronics.
"We found that the risk posed by these portable devices is higher than previously believed," said aircraft electronics expert Bill Strauss.
"These devices can disrupt normal operation of key cockpit instruments, especially Global Positioning Systems receivers, which are increasingly vital for safe landings," he said.
While standard airline safety warnings inform passengers they must keep their phones switched off during flights, this has long been dismissed as an unnecessary precaution.
Until now, the main logic behind the phone ban has been that high speed planes full of passengers making calls cause massive disruption to regionalized cellular networks as they sweep overhead.
