Operators of commercial airplanes have reported numerous cases of portable electronic devices affecting airplane systems during flight. These devices, including laptop and palmtop computers, audio players/recorders, electronic games, cell phones, compact-disc players, electronic toys, and laser pointers, have been suspected of causing such anomalous events as autopilot disconnects, erratic flight deck indications, airplanes turning off course, and uncommanded turns. Boeing has recommended that devices suspected of causing these anomalies be turned off during critical stages of flight (takeoff and landing). The company also recommends prohibiting the use of devices that intentionally transmit electromagnetic signals, such as cell phones, during all phases of flight. The U.S. Federal Communications Commission already prohibits the use of cell phones during flight. In addition, the U.S. Federal Aviation Administration issued Federal Aviation Regulation 91.21 to make operators responsible for governing the use of portable electronic devices on their airplanes. Electromagnetic interference (EMI) from passenger-carried portable electronic devices (PED) on commercial airplanes has been reported as being responsible for anomalous events during flight. The operation of PEDs produces uncontrolled electromagnetic emissions that could interfere with airplane systems. Airplane systems are tested to rigorous electromagnetic standards to establish and provide control of the electromagnetic characteristics and compatibility of these systems. However, PEDs are not subject to these same equipment qualification and certification processes. Though many cases of EMI have been reported over the years, with PEDs suspected as the cause, it has proven almost impossible to duplicate these events. Boeing has participated in several related activities and has revised its all-model service letter for concurrence with the U.S. Federal Aviation Administration (FAA) advisory circular (AC) on the use of cell phones while airplanes are on the ground. However, operators and their flight crews are ultimately responsible for deciding whether to allow the use of PEDs.