By 9:20, Indianapolis Center learned that there were other hijacked aircraft, and began to doubt its initial assumption that American 77 had crashed.
( ( By 9:20 ) ( , ( ( Indianapolis Center ) ( ( ( ( ( learned ( that ( there ( were ( other ( hijacked aircraft ) ) ) ) ) ) , ) and ) ( began ( to ( ( doubt ( its ( initial assumption ) ) ) ( that ( ( American 77 ) ( had crashed ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN By) (NP (CD 9:20))) (, ,) (NP (NNP Indianapolis) (NNP Center)) (VP (VP (VBD learned) (SBAR (IN that) (S (NP (EX there)) (VP (VBD were) (NP (JJ other) (JJ hijacked) (NN aircraft)))))) (, ,) (CC and) (VP (VBD began) (S (VP (TO to) (VP (VB doubt) (NP (PRP$ its) (JJ initial) (NN assumption)) (SBAR (IN that) (S (NP (NNP American) (CD 77)) (VP (VBD had) (VP (VBD crashed)))))))))) (. .)))
Indianapolis Center learned that another aircraft was hijacked.
( ( Indianapolis Center ) ( ( learned ( that ( ( another aircraft ) ( was hijacked ) ) ) ) . ) )
(ROOT (S (NP (NNP Indianapolis) (NNP Center)) (VP (VBD learned) (SBAR (IN that) (S (NP (DT another) (NN aircraft)) (VP (VBD was) (VP (VBN hijacked)))))) (. .)))