 In many countries, ATC provides services to all private, military, and commercial aircraft operating within its airspace.Depending on the type of flight and the class of airspace, ATC may issue "instructions" that pilots are required to obey, or "advisories" (known as "flight information" in some countries) that pilots may, at their discretion, disregard.The pilot in command is the final authority for the safe operation of the aircraft and may, in an emergency, deviate from ATC instructions to the extent required to maintain safe operation of their aircraft.