(S (S (S (BASENP (NNS Investigators)) (VP (VP (ADVP (RB initially)) (VP (VBD struggled) (S (VP (TO to) (VP (VP (VB produce) (BASENP (JJ enough) (NN ice))) (PP (IN under) (BASENP (NN test) (NNS conditions)))))))) (CC but) (VP (VBP have) (VP (ADVP (RB now)) (VP (VBN found) (SBAR (IN that) (S (PP (IN at) (BASENP (JJ high) (NN concentration))) (COMMA ,) (S (BASENP (NN fuel)) (VP (MD can) (VP (VP (VP (VB form) (BASENP (NN ice))) (PP (IN at) (BASENP (ADJP (RB very) (JJ low)) (NNS temperatures)))) (PP (IN in) (NP (BASENP (JJ enough) (NN quantity)) (S (VP (TO to) (VP (ADVP (RB seriously)) (VP (VB restrict) (BASENP (NN fuel) (NN flow)))))))))))))))))) (COMMA ,) (PP (VBG according) (PP (TO to) (NP (BASENP (DT a) (JJ new) (JJ interim) (NN report)) (PP (IN by) (BASENP (DT the) (NNP AAIB))))))) (PERIOD .))