Concerns over the safety of other aircraft began to mount.
( ( Concerns ( over ( ( the safety ) ( of ( other aircraft ) ) ) ) ) ( ( began ( to mount ) ) . ) )
(ROOT (S (NP (NP (NNS Concerns)) (PP (IN over) (NP (NP (DT the) (NN safety)) (PP (IN of) (NP (JJ other) (NN aircraft)))))) (VP (VBD began) (S (VP (TO to) (VP (VB mount))))) (. .)))
Concerns concerning the other aircraft's safety began to mount.
( ( Concerns ( concerning ( ( the ( other ( aircraft 's ) ) ) safety ) ) ) ( ( began ( to mount ) ) . ) )
(ROOT (S (NP (NP (NNS Concerns)) (PP (VBG concerning) (NP (NP (DT the) (JJ other) (NN aircraft) (POS 's)) (NN safety)))) (VP (VBD began) (S (VP (TO to) (VP (VB mount))))) (. .)))