(S (S (BASENP (DT The) (NNP United) (NNPS States)) (VP (VBZ is) (VP (VBG replacing) (NP (BASENP (JJ emergency) (NN oxygen) (NNS handles)) (PP (IN on) (BASENP (PRPD its) (NN 170) (NN jet) (NNS fighters))))))) (PERIOD .))