In the interest of expediting traffic, a clearance for immediate take-off may be issued to an aircraft before it enters the runway. On acceptance of such clearance the aircraft shall taxi out to the runway and take off in one continuous movement.

According ICAO Standards and Recommended Practices (SARPS), in the interest of expediting traffic, a clearance for immediate take-off may be issued to an aircraft before it enters the runway. On acceptance of such clearance the aircraft shall taxi out to the runway and take off in one continuous movement.

The controller authorizes the aircraft to take off. This is the one and only clearance that gives a pilot permission to take off. If you are holding short of a runway, this clearance also gives you permission to enter it and align.

An ATC clearance means an authorization by ATC, for the purpose of preventing collision between known aircraft, for an aircraft to proceed under specified conditions within controlled airspace. IT IS NOT AUTHORIZATION FOR A PILOT TO DEVIATE FROM ANY RULE, REGULATION, OR MINIMUM ALTITUDE NOR TO CONDUCT UNSAFE OPERATION OF THE AIRCRAFT.

While holding short of the runway awaiting the "Taxi to Position" or "Take-Off Clearance", there are often about 5 or 6 items left to clear up on the "Before take-off" checklist. When cleared to position, the first officer usually actions the items as the captain taxis the airplane.