That aircraft was United 93.
( ( That aircraft ) ( ( was ( United 93 ) ) . ) )
(ROOT (S (NP (DT That) (NN aircraft)) (VP (VBD was) (NP (NNP United) (CD 93))) (. .)))
The plane was United 11.
( ( The plane ) ( ( was ( United 11 ) ) . ) )
(ROOT (S (NP (DT The) (NN plane)) (VP (VBD was) (NP (NNP United) (CD 11))) (. .)))