The other aircraft referred to by New York Center was United 175.
( ( ( The ( other aircraft ) ) ( ( referred to ) ( by ( New ( York Center ) ) ) ) ) ( ( was ( United 175 ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJ other) (NN aircraft)) (VP (VBN referred) (S (VP (TO to))) (PP (IN by) (NP (NNP New) (NNP York) (NNP Center))))) (VP (VBD was) (NP (NNP United) (CD 175))) (. .)))
One of the aircraft that New York Center referred to was Untied 175.
( ( One ( of ( ( the aircraft ) ( that ( ( New ( York Center ) ) ( referred to ) ) ) ) ) ) ( ( was ( Untied 175 ) ) . ) )
(ROOT (S (NP (NP (CD One)) (PP (IN of) (NP (NP (DT the) (NN aircraft)) (SBAR (IN that) (S (NP (NNP New) (NNP York) (NNP Center)) (VP (VBD referred) (PP (TO to)))))))) (VP (VBD was) (NP (NNP Untied) (CD 175))) (. .)))