RTCA, an organization which advises the aviation industry, has recommended that all airlines ban such devices from being used during" critical" stages of flight, particularly take-off and landing. Some experts have gone further, calling for a total ban during all flights. Currently, rules on using these devices are left up to individual airlines. And although some airlines prohibit passengers from using such equipment during ail flights. Currently, rules on using these devices are left up to individual airiness. And although some airlines prohibit passengers from using such equipment during take-off and landing, most are reluctant to enforce a total ban, given that many passengers want to work during flights.
The difficulty is predicting how electromagnetic fields might affect an aircraft' s computers. Experts know that portable devices emit radiation which affects those wavelengths which aircraft' s use for navigation and communication. But because they have not been able to reproduce these effects in a laboratory, they have no way of knowing whether the interference might be dangerous or not.
The fact that aircrafts may be vulnerable to interference raises the risk that terrorists may use radio systems in order to damage navigation equipment. As worrying, though, is the passenger who can' t hear the instructions to turn off his radio because the music' s too loud.
The passage is mainly about______.

A. a new regulation for all airlines
B. the defects of electronic devices
C. a possible cause of aircraft crashes
D. effective safety measures for air flight