We are returning to the airport.
( We ( ( are ( returning ( to ( the airport ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VBP are) (VP (VBG returning) (PP (TO to) (NP (DT the) (NN airport))))) (. .)))
This was announced over the PA system.
( This ( ( was ( announced ( over ( the ( PA system ) ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBD was) (VP (VBN announced) (PP (IN over) (NP (DT the) (NNP PA) (NN system))))) (. .)))