At 8:51, the flight deviated from its assigned altitude, and a minute later New York air traffic controllers began repeatedly and unsuccessfully trying to contact it.
( ( At 8:51 ) ( , ( ( ( ( ( ( the flight ) ( deviated ( from ( its ( assigned altitude ) ) ) ) ) , ) and ) ( ( ( a minute ) later ) ( ( New ( York ( air ( traffic controllers ) ) ) ) ( began ( ( repeatedly and ) ( unsuccessfully ( trying ( to ( contact it ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (PP (IN At) (NP (CD 8:51))) (, ,) (S (NP (DT the) (NN flight)) (VP (VBD deviated) (PP (IN from) (NP (PRP$ its) (VBN assigned) (NN altitude))))) (, ,) (CC and) (S (ADVP (NP (DT a) (NN minute)) (RB later)) (NP (NNP New) (NNP York) (NN air) (NN traffic) (NNS controllers)) (VP (VBD began) (UCP (ADVP (RB repeatedly)) (CC and) (VP (ADVP (RB unsuccessfully)) (VBG trying) (S (VP (TO to) (VP (VB contact) (NP (PRP it))))))))) (. .)))
At 8:51, it was still maintaining its assigned altitude.
( ( At 8:51 ) ( , ( it ( ( was ( still ( maintaining ( its ( assigned altitude ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN At) (NP (CD 8:51))) (, ,) (NP (PRP it)) (VP (VBD was) (VP (ADVP (RB still)) (VBG maintaining) (NP (PRP$ its) (VBN assigned) (NN altitude)))) (. .)))