Smooth, as wood (4)
(Other definitions for sand that I've seen before include "Grains of quartz" , "Beach/desert material" , "Grains by the sea" , "Smooth with abrasive paper" , "woman writer Chopin loved" .)
(Other definitions for plane that I've seen before include "Smooth" , "barked?" , "Nepal (anag.)" , "that soars into the sky" , "Form of transport" .)