At 8:21, American 11 turned off its transponder, immediately degrading the information available about the aircraft.
( ( At 8:21 ) ( , ( ( American 11 ) ( ( ( ( ( turned off ) ( its transponder ) ) , ) ( immediately ( degrading ( ( the information ) ( available ( about ( the aircraft ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN At) (NP (CD 8:21))) (, ,) (NP (NNP American) (CD 11)) (VP (VBD turned) (PRT (RP off)) (NP (PRP$ its) (NN transponder)) (, ,) (S (ADVP (RB immediately)) (VP (VBG degrading) (S (NP (DT the) (NN information)) (ADJP (JJ available) (PP (IN about) (NP (DT the) (NN aircraft)))))))) (. .)))
American 11 turned kept its transponder on during the entire flight providing full information on the horrific tragedy of 9/11. 
( ( ( American 11 ) turned ) ( ( ( kept ( its transponder ) ) ( on ( during ( ( the ( entire flight ) ) ( ( providing ( full information ) ) ( on ( ( the ( horrific tragedy ) ) ( of 9/11 ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP American) (CD 11)) (VP (VBN turned))) (VP (VBD kept) (NP (PRP$ its) (NN transponder)) (PP (IN on) (IN during) (NP (NP (DT the) (JJ entire) (NN flight)) (VP (VBG providing) (NP (JJ full) (NN information)) (PP (IN on) (NP (NP (DT the) (JJ horrific) (NN tragedy)) (PP (IN of) (NP (CD 9/11))))))))) (. .)))