imposed by various international aviation agencies, ultra-low-power devices, such as picocells, have been developed. Reasons for this include improved security, reduction of interference, and to allow safe in-flight use of mobile phones. Many airline companies have now added such equipment to their aircraft. More are expected to do so in the coming years. Electromagnetic interference Electromagnetic interference to aircraft systems is a common argument offered for banning mobile phones (and other passenger electronic devices) on planes. Theoretically, active radio transmitters such as mobile phones, walkie–talkies, portable computers or gaming devices may interfere with the aircraft. Non-transmitting electronic devices also emit electromagnetic radiation, although typically at a lower power level, and could also theoretically affect the aircraft electronics. Collectively, any of these may be referred to as portable electronic devices (PEDs). A NASA publication details the fifty most recent reports to the Aviation Safety Reporting System (ASRS) regarding "avionics problems that may result from the influence of passenger electronic devices." The nature of these reports varies widely. Some merely describe passengers' interactions with flight crews when asked to stop using an electronic device. Other reports amount to crews reporting an anomaly experienced at the same time a passenger was witnessed using a mobile phone. A few reports state that interference to aircraft systems was observed to appear and disappear as that particular suspect device was turned on and off. One entry in the ASRS, designated ACN: 440557, reports a clear link where a passenger's DVD player induced a 30-degree error in the display of the aircraft's heading, each time the player was switched on. However, this report dates back to 1999 and involves a Boeing 727, an old type of aircraft that is no longer in use by airlines today. A 2003 study involved three months of testing with RF spectrum analyzers and other instruments aboard regular commercial flights, and one passage reads: A 2000 study by the British Civil Aviation Authority found that a mobile phone, when used near the cockpit or other avionics equipment location, will exceed safety levels for older equipment (compliant with 1984 standards). Such equipment is still in use, even in new aircraft. Therefore, the report concludes, the current policy, which restricts the use of mobile phones on all aircraft while the engines are running, should remain in force. Critics of the ban doubt that small battery-powered devices would have any significant influence on a commercial