(S (S (SBAR (BASENP (NN Three) (NNS days)) (SBAR (IN after) (S (BASENP (DT a) (NNP US) (NNP Navy) (NN helicopter)) (VP (VP (VBD collided) (PP (IN with) (BASENP (DT a) (NNP US) (NNP Coast) (NNP Guard) (NN airplane)))) (PP (IN off) (NP (BASENP (DT the) (NN coast)) (PP (IN of) (BASENP (NNP California))))))))) (COMMA ,) (S (NP (DT a) (NP (BASENP (NN search)) (CC and) (BASENP (NN rescue) (NN mission)))) (VP (VBZ is) (VP (VBG ongoing) (PP (IN for) (NP (BASENP (DT the) (NN nine) (NN crew)) (ADJP (JJ onboard) (BASENP (DT the) (NN two) (NN aircraft))))))))) (PERIOD .))