Some of the air leaks radially outwards, to seal {HEAD ~ the gas annulus} against {TAIL ~ hot gas leaks} onto the face of the turbine disc 
against
Some of the air leaks radially outwards , to seal { HEAD ~ the gas annulus } against { TAIL ~ hot gas leaks } onto the face of the turbine disc
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH