But another aircraft was heading toward Washington, an aircraft about which NORAD had heard  United 93.
( But ( ( another aircraft ) ( ( was ( heading ( toward ( ( Washington , ) ( ( an aircraft ) ( ( about which ) ( NORAD ( had ( heard ( United 93 ) ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (CC But) (NP (DT another) (NN aircraft)) (VP (VBD was) (VP (VBG heading) (PP (IN toward) (NP (NP (NNP Washington)) (, ,) (NP (NP (DT an) (NN aircraft)) (SBAR (WHPP (IN about) (WHNP (WDT which))) (S (NP (NNP NORAD)) (VP (VBD had) (VP (VBN heard) (NP (NNP United) (CD 93))))))))))) (. .)))
There were no further aircrafts heading towards Washington.
( There ( ( were ( ( no ( further aircrafts ) ) ( heading ( towards Washington ) ) ) ) . ) )
(ROOT (S (NP (EX There)) (VP (VBD were) (NP (NP (DT no) (JJ further) (NNS aircrafts)) (VP (VBG heading) (PP (IN towards) (NP (NNP Washington)))))) (. .)))