The controller checked to see if American Airlines could establish communication with American 11.
( ( The controller ) ( ( checked ( to ( see ( if ( ( American Airlines ) ( could ( ( establish communication ) ( with ( American 11 ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN controller)) (VP (VBD checked) (S (VP (TO to) (VP (VB see) (SBAR (IN if) (S (NP (NNP American) (NNPS Airlines)) (VP (MD could) (VP (VB establish) (NP (NN communication)) (PP (IN with) (NP (NNP American) (CD 11))))))))))) (. .)))
The controller checked several different frequencies and signals to find American 11.
( ( The controller ) ( ( ( ( checked ( several ( different frequencies ) ) ) and ) ( signals ( to ( find ( American 11 ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN controller)) (VP (VP (VBD checked) (NP (JJ several) (JJ different) (NNS frequencies))) (CC and) (VP (VBZ signals) (S (VP (TO to) (VP (VB find) (NP (NNP American) (CD 11))))))) (. .)))