That message and all subsequent attempts to contact the flight were not acknowledged.
( ( ( ( That message ) and ) ( ( all ( subsequent attempts ) ) ( to ( contact ( the flight ) ) ) ) ) ( ( ( were not ) acknowledged ) . ) )
(ROOT (S (NP (NP (DT That) (NN message)) (CC and) (NP (NP (DT all) (JJ subsequent) (NNS attempts)) (SBAR (S (VP (TO to) (VP (VB contact) (NP (DT the) (NN flight)))))))) (VP (VBD were) (RB not) (VP (VBN acknowledged))) (. .)))
Dozens of attempts were made to contact the flight, but none got a response.
( ( ( ( ( ( Dozens ( of attempts ) ) ( were ( made ( to ( contact ( the flight ) ) ) ) ) ) , ) but ) ( none ( got ( a response ) ) ) ) . )
(ROOT (S (S (NP (NP (NNS Dozens)) (PP (IN of) (NP (NNS attempts)))) (VP (VBD were) (VP (VBN made) (S (VP (TO to) (VP (VB contact) (NP (DT the) (NN flight)))))))) (, ,) (CC but) (S (NP (NN none)) (VP (VBD got) (NP (DT a) (NN response)))) (. .)))