just been at the airport and also listning to tower and on some planes some small some larger they say line up back track. then the planes goes to the end of the runway turns around and goes. but others just turn at alpha 1 and take off.??

 

 

soul.

They are going backwards on the runway to use all the available runway. Other aircraft my not need it all and are able to takeoff on shorter runway lengths at intersections of taxiways and the runway.