Prior to 9/11, it was understood that an order to shoot down a commercial aircraft would have to be issued by the National Command Authority (a phrase used to describe the president and secretary of defense).
( ( Prior ( to 9/11 ) ) ( , ( it ( ( was ( understood ( that ( ( an ( order ( to ( ( shoot down ) ( a ( commercial aircraft ) ) ) ) ) ) ( would ( have ( to ( be ( issued ( by ( ( the ( National ( Command Authority ) ) ) ( -LRB- ( ( ( a phrase ) ( used ( to ( describe ( ( the ( ( president and ) secretary ) ) ( of defense ) ) ) ) ) ) -RRB- ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (RB Prior) (PP (TO to) (NP (CD 9/11)))) (, ,) (NP (PRP it)) (VP (VBD was) (VP (VBN understood) (SBAR (IN that) (S (NP (DT an) (NN order) (S (VP (TO to) (VP (VB shoot) (PRT (RP down)) (NP (DT a) (JJ commercial) (NN aircraft)))))) (VP (MD would) (VP (VB have) (S (VP (TO to) (VP (VB be) (VP (VBN issued) (PP (IN by) (NP (NP (DT the) (NNP National) (NNP Command) (NNP Authority)) (PRN (-LRB- -LRB-) (NP (NP (DT a) (NN phrase)) (VP (VBN used) (S (VP (TO to) (VP (VB describe) (NP (NP (DT the) (NN president) (CC and) (NN secretary)) (PP (IN of) (NP (NN defense))))))))) (-RRB- -RRB-)))))))))))))) (. .)))
Now you can shoot any aircraft you want. 
( Now ( you ( ( can ( shoot ( ( any aircraft ) ( you want ) ) ) ) . ) ) )
(ROOT (S (ADVP (RB Now)) (NP (PRP you)) (VP (MD can) (VP (VB shoot) (NP (NP (DT any) (NN aircraft)) (SBAR (S (NP (PRP you)) (VP (VBP want))))))) (. .)))