The flight did not respond.
( ( The flight ) ( ( ( did not ) respond ) . ) )
(ROOT (S (NP (DT The) (NN flight)) (VP (VBD did) (RB not) (VP (VB respond))) (. .)))
The flight did not respond because it had crashed.  
( ( The flight ) ( ( ( did not ) ( respond ( because ( it ( had crashed ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN flight)) (VP (VBD did) (RB not) (VP (VB respond) (SBAR (IN because) (S (NP (PRP it)) (VP (VBD had) (VP (VBD crashed))))))) (. .)))