{TAIL ~ An airspace} is divide into {HEAD ~ a set} of grid cells, and a flight path is established between the initial point and the destination point 
{ TAIL ~ An airspace } is divide into { HEAD ~ a set } of grid cells , and a flight path is established between the initial point and the destination point
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH