(S (S (NP (CC Both) (NP (BASENP (DT the) (NNP NTSB)) (CC and) (BASENP (DT the) (NNP AAIB)))) (VP (ADVP (RB also)) (VP (VP (VP (VBD sent) (BASENP (NNS letters))) (PP (TO to) (NP (BASENP (DT the) (NNP US) (NNP Federal) (NNP Aviation) (NNP Administration)) (CC and) (BASENP (DT the) (NNP European) (NNP Aviation) (NNP Safety) (NNP Agency))))) (S (VP (VBG requesting) (SBAR (S (NP (BASENP (DT the) (NN installment)) (PP (IN of) (BASENP (DT the) (VBN modified) (NN component)))) (VP (VB be) (ADJP (JJ mandatory)))))))))) (PERIOD .))