The reply format is usually referred to as a "code" from a transponder, which is used to determine detailed information from a suitably equipped aircraft.
A separate type of response called "Ident" can be initiated from the airplane by pressing a button on the transponder control panel.
Mode A and C responses are used to help air traffic controllers identify a particular aircraft's position and altitude on a radar screen, in order to maintain separation.
[10] In 2009 the ICAO published an "extended" form of Mode S with more message formats to use with ADS-B;[11] it was further refined in 2012.
Mode-S data has the potential to contain the aircraft's movement vectors in relation to the Earth and its atmosphere.
[13] Deriving winds (and temperatures from the Mach number and true airspeed) was developed simultaneously by Siebren de Haan of the KNMI and Edmund Stone of the Met Office.
The Met Office together with KNMI and FlightRadar24 are actively developing an expanded capability including data from every continent other than Antarctica.