 At controlled airports, take-off or landing clearances do not authorize the pilot to reverse course and backtrack along the runway, unless specified by air traffic control.At uncontrolled airports, pilots are recommended to broadcast their intentions while backtracking in the interest of safety; for example, the statement "Entering and backtracking runway 36" would indicate the aircraft is taxiing along a magnetic heading of 180 degrees, against the flow of traffic.An infamous and rare example of where backtracking was used for large commercial aircraft was the Tenerife airport disaster, where two Boeing 747s at Tenerife North Airport were required to backtaxi in order to position themselves for take-off.