Cabin service would have begun.
( ( Cabin service ) ( ( would ( have begun ) ) . ) )
(ROOT (S (NP (NN Cabin) (NN service)) (VP (MD would) (VP (VB have) (VP (VBN begun)))) (. .)))
They were about to start cabin service.
( They ( ( were ( about ( to ( start ( cabin service ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBD were) (VP (IN about) (S (VP (TO to) (VP (VB start) (NP (NN cabin) (NN service))))))) (. .)))