A study by researchers in the Department of Engineering and Public Policy (DEPP) at Carnegie Mellon University has found that the use of mobile phones on aircraft is more dangerous than previously thought.

The researchers, with support from the Federal Aviation Administration, three major airlines and the Transportation Security Agency, criss-crossed the northeast US on commercial flights, monitoring radio emissions from passenger use of cell phones and other electronic devices.

They tracked the radio emissions via a broadband antenna attached to a compact portable spectrum analyser that fitted into an innocuous carry-on bag.

"A laptop computer controlled the system and logged the data," said Granger Morgan, head of the DEPP.

"While we looked primarily at wireless phones, we also discovered that emissions from other portable electronic devices were problematic."

The researchers found that between one and four phone calls are typically made from every commercial flight in the northeast US. Some of these calls are made during critical flight stages such as climb-out or final approach.

The investigators reported that such activity could cause accidents. "We found that the risk posed by these portable devices is higher than previously believed," said Bill Strauss, an expert in aircraft electromagnetic compatibility at the Naval Air Warfare Centre in Maryland.

"These devices can disrupt normal operation of key cockpit instruments, especially GPS receivers which are increasingly vital for safe landings."