(S (S (S (BASENP (DT The) (JJ experienced) (NN 31-year-old)) (VP (VBD was) (PP (IN on) (BASENP (DT a) (NN night) (NN mission))))) (SBAR (WHADVP (WRB when)) (S (BASENP (PRPD his) (NN aircraft)) (VP (VP (VBD crashed) (ADVP (RB nose-down))) (PP (IN among) (BASENP (NNS mountains))))))) (PERIOD .))