The most recent hijacking that involved U.S. air traffic controllers, FAA management, and military coordination had occurred in 1993.
( ( ( The ( most ( recent hijacking ) ) ) ( that ( involved ( ( ( ( ( ( U.S. ( air ( traffic controllers ) ) ) , ) ( FAA management ) ) , ) and ) ( military coordination ) ) ) ) ) ( ( had ( occurred ( in 1993 ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (RBS most) (JJ recent) (NN hijacking)) (SBAR (WHNP (WDT that)) (S (VP (VBD involved) (NP (NP (NNP U.S.) (NN air) (NN traffic) (NNS controllers)) (, ,) (NP (NNP FAA) (NN management)) (, ,) (CC and) (NP (JJ military) (NN coordination))))))) (VP (VBD had) (VP (VBN occurred) (PP (IN in) (NP (CD 1993))))) (. .)))
The most recent hijacking that involved three air-traffic related organizations had been in 1993.
( ( ( The ( most ( recent hijacking ) ) ) ( that ( involved ( ( three air-traffic ) ( related organizations ) ) ) ) ) ( ( had ( been ( in 1993 ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (RBS most) (JJ recent) (NN hijacking)) (SBAR (WHNP (WDT that)) (S (VP (VBD involved) (NP (NP (CD three) (NN air-traffic)) (VP (VBN related) (NP (NNS organizations)))))))) (VP (VBD had) (VP (VBN been) (PP (IN in) (NP (CD 1993))))) (. .)))