He could have learned of this from messages being sent by United Airlines to the cockpits of its transcontinental flights, including Flight 93, warning of cockpit intrusion and telling of the New York attacks.
( He ( ( could ( have ( ( learned ( of ( this ( from messages ) ) ) ) ( ( ( ( ( being ( ( ( ( sent ( by ( United Airlines ) ) ) ( to ( ( the cockpits ) ( of ( its ( transcontinental flights ) ) ) ) ) ) , ) ( including ( Flight 93 ) ) ) ) , ) ( warning ( of ( cockpit intrusion ) ) ) ) and ) ( telling ( of ( the ( New ( York attacks ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP He)) (VP (MD could) (VP (VB have) (VP (VBN learned) (PP (IN of) (NP (NP (DT this)) (PP (IN from) (NP (NNS messages))))) (S (VP (VP (VBG being) (VP (VBN sent) (PP (IN by) (NP (NNP United) (NNPS Airlines))) (PP (TO to) (NP (NP (DT the) (NNS cockpits)) (PP (IN of) (NP (PRP$ its) (JJ transcontinental) (NNS flights))))) (, ,) (PP (VBG including) (NP (NNP Flight) (CD 93))))) (, ,) (VP (VBG warning) (PP (IN of) (NP (NN cockpit) (NN intrusion)))) (CC and) (VP (VBG telling) (PP (IN of) (NP (DT the) (NNP New) (NNP York) (NNS attacks))))))))) (. .)))
United Airlines sent some messages to the cockpits of transcontinental flights.
( ( United Airlines ) ( ( ( sent ( some messages ) ) ( to ( ( the cockpits ) ( of ( transcontinental flights ) ) ) ) ) . ) )
(ROOT (S (NP (NNP United) (NNPS Airlines)) (VP (VBD sent) (NP (DT some) (NNS messages)) (PP (TO to) (NP (NP (DT the) (NNS cockpits)) (PP (IN of) (NP (JJ transcontinental) (NNS flights)))))) (. .)))