if you have fps drops near on on runways , try to comment the ANIM_hide and ANIM_show lines in the anim blocks of airports objects files (.obj extension) having "ANIM_show 0 0 sim/weather/runway_friction" (dry weather)
An example : Orbx EGLL PBE_EGLC_GP_SOIL01.obj (comment the lines in the other obj files files found too)
#ANIM_hide 1 2 sim/weather/runway_friction
#ANIM_show 0 0 sim/weather/runway_friction
TRIS 0 2916
ANIM_begin and ANIM_end commands can be commented too, thought I found not necessary
But be aware that switching between the dry texture and the wet texture (normally present in another object , with values for ANIM_hide and ANIM_show inverted) will not work anymore.