We're told that one aircraft is down but we do not have a pilot report that did it.
( ( ( ( We ( 're ( told ( that ( ( one aircraft ) ( is down ) ) ) ) ) ) but ) ( we ( ( do not ) ( have ( ( a ( pilot report ) ) ( that ( did it ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (PRP We)) (VP (VBP 're) (VP (VBN told) (SBAR (IN that) (S (NP (CD one) (NN aircraft)) (VP (VBZ is) (ADJP (RP down)))))))) (CC but) (S (NP (PRP we)) (VP (VBP do) (RB not) (VP (VB have) (NP (NP (DT a) (NN pilot) (NN report)) (SBAR (WHNP (WDT that)) (S (VP (VBD did) (NP (PRP it))))))))) (. .)))
We do not have a pilot report that took down the aircraft. 
( We ( ( ( do not ) ( have ( ( a ( pilot report ) ) ( that ( ( took down ) ( the aircraft ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VBP do) (RB not) (VP (VB have) (NP (NP (DT a) (NN pilot) (NN report)) (SBAR (WHNP (WDT that)) (S (VP (VBD took) (PRT (RP down)) (NP (DT the) (NN aircraft)))))))) (. .)))