(S (S (BASENP (DT This)) (VP (VBZ is) (VP (VBN said) (S (VP (TO to) (VP (VB be) (NP (NP (BASENP (NNP Russia) (POS 's)) (BASENP (JJS worst) (JJ commercial) (NN air) (NN disaster))) (PP (IN since) (NP (BASENP (NNP August) (NN 2006)) (SBAR (WHADVP (WRB when)) (S (S (BASENP (NN 170) (NNS people)) (VP (VBD died))) (SBAR (IN after) (S (NP (NP (BASENP (DT a) (NNP Tupolev) (NNP Tu-154) (NN passenger) (NN jet)) (COMMA ,) (BASENP (NN flight) (NN 612))) (PRN (COMMA ,) (VP (VBN owned) (PP (IN by) (BASENP (ADJP (JJ St.) (JJ Petersburg-based)) (NNP Pulkovo) (NNPS Airlines)))) (COMMA ,))) (VP (VBD crashed) (PP (IN in) (BASENP (DT the) (NNP Ukraine))))))))))))))))) (PERIOD .))