According to contemporaneous notes, at 9:55 the Vice President was still on the phone with the President advising that three planes were missing and one had hit the Pentagon.
( ( According ( to ( contemporaneous notes ) ) ) ( , ( ( ( ( ( at 9:55 ) ( ( the ( Vice President ) ) ( ( ( was still ) ( on ( ( the phone ) ( with ( the President ) ) ) ) ) ( advising ( that ( ( three planes ) ( were missing ) ) ) ) ) ) ) and ) ( one ( had ( hit ( the Pentagon ) ) ) ) ) . ) ) )
(ROOT (S (PP (VBG According) (PP (TO to) (NP (JJ contemporaneous) (NNS notes)))) (, ,) (S (PP (IN at) (NP (CD 9:55))) (NP (DT the) (NNP Vice) (NNP President)) (VP (VBD was) (ADVP (RB still)) (PP (IN on) (NP (NP (DT the) (NN phone)) (PP (IN with) (NP (DT the) (NNP President))))) (S (VP (VBG advising) (SBAR (IN that) (S (NP (CD three) (NNS planes)) (VP (VBD were) (ADJP (VBG missing))))))))) (CC and) (S (NP (PRP one)) (VP (VBD had) (VP (VBN hit) (NP (DT the) (NNP Pentagon))))) (. .)))
The Vice President was informing the President.
( ( The ( Vice President ) ) ( ( was ( informing ( the President ) ) ) . ) )
(ROOT (S (NP (DT The) (NNP Vice) (NNP President)) (VP (VBD was) (VP (VBG informing) (NP (DT the) (NNP President)))) (. .)))