Because Ballinger was still responsible for his other flights as well as Flight 175, his warning message was not transmitted to Flight 93 until 9:23.
( ( Because ( Ballinger ( ( was still ) ( responsible ( for ( ( ( his ( other flights ) ) ( as ( well as ) ) ) ( Flight 175 ) ) ) ) ) ) ) ( , ( ( his ( warning message ) ) ( ( ( was not ) ( ( transmitted ( to ( Flight 93 ) ) ) ( until 9:23 ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN Because) (S (NP (NNP Ballinger)) (VP (VBD was) (ADVP (RB still)) (ADJP (JJ responsible) (PP (IN for) (NP (NP (PRP$ his) (JJ other) (NNS flights)) (CONJP (RB as) (RB well) (IN as)) (NP (NNP Flight) (CD 175)))))))) (, ,) (NP (PRP$ his) (NN warning) (NN message)) (VP (VBD was) (RB not) (VP (VBN transmitted) (PP (TO to) (NP (NNP Flight) (CD 93))) (PP (IN until) (NP (CD 9:23))))) (. .)))
Someone was trying to warn the plane about a highjacking.
( Someone ( ( was ( trying ( to ( warn ( ( the plane ) ( about ( a highjacking ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NN Someone)) (VP (VBD was) (VP (VBG trying) (S (VP (TO to) (VP (VB warn) (NP (NP (DT the) (NN plane)) (PP (IN about) (NP (DT a) (NN highjacking))))))))) (. .)))