The onboard electronics used for piloting an aircraft are called avionics. Avionics include communications and navigation systems, autopilots, and electronic flight management systems (FMS). Onboard electronics that are unrelated to piloting tasks, such as video systems for passengers, are often considered avionics as well.
Radiotelephone (two way voice radio) systems have been installed in aircraft since before World War II, and have been widely used for mission coordination and air traffic control. Early systems used vacuum tubes, and because of their weight and size, were installed out of the way with only a control head in place in the flight deck. Standardization on VHF frequences occurred shortly after World War II, and transistor radio systems replaced the tube-based systems shortly afterward. Only minor changes have been made to these systems since 1960s.
The earliest navigation systems required the pilot or navigator to wear headphones and listen to the relative volume of tones in each ear to determine which way to steer on course.
Later, navigation systems developed along three separate paths:
For a time, LORAN systems, which provide navigational guidance over large areas, were popular particularly for general aviation use. They have declined in popularity with the commercial availability of GPS service.
GPS receivers have made some inroads into the flight deck but remain a supplemental source of navigation.
A basic 'mode A' transponder responds with a 4-digit code with each digit ranging from 0 to 7. This is called a 4,096 code transponder. This pilot sets the code according to the type and status of the flight or as directed by air traffic control.
A 'mode C' transponder also replies with the pressure altitude of the aircraft encoded to the nearest 100 feet. Modern 'mode S' transponders can respond with a longer digital identifier that is unique for each aircraft (thus allowing each aircraft to be uniquely identified even when there is no voice communication between the aircraft and air traffic control) and can receive digital traffic information from air traffic controlradar systems and display them for the pilot.
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