Crisis managers at the FAA and the airlines did not yet act to warn other aircraft.
( ( ( Crisis managers ) ( at ( ( ( the FAA ) and ) ( the airlines ) ) ) ) ( ( ( ( did not ) yet ) ( act ( to ( warn ( other aircraft ) ) ) ) ) . ) )
(ROOT (S (NP (NP (JJ Crisis) (NNS managers)) (PP (IN at) (NP (NP (DT the) (NNP FAA)) (CC and) (NP (DT the) (NNS airlines))))) (VP (VBD did) (RB not) (ADVP (RB yet)) (VP (VB act) (S (VP (TO to) (VP (VB warn) (NP (JJ other) (NN aircraft))))))) (. .)))
Crisis managers had failed to warn aircraft until now.
( ( Crisis managers ) ( ( had ( failed ( to ( ( warn aircraft ) ( until now ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Crisis) (NNS managers)) (VP (VBD had) (VP (VBN failed) (S (VP (TO to) (VP (VB warn) (NP (NN aircraft)) (PP (IN until) (NP (RB now)))))))) (. .)))