Planes, as in plural.
( Planes ( , ( ( as ( in plural ) ) . ) ) )
(ROOT (FRAG (NP (NNS Planes)) (, ,) (PP (RB as) (IN in) (NP (NN plural))) (. .)))
Only one plane.
( ( Only one ) ( plane . ) )
(ROOT (FRAG (NP (RB Only) (CD one)) (NP (NN plane)) (. .)))