they might be but not at not at the human factors level
( they ( might ( be ( ( but ( ( not ( at not ) ) ( at ( the ( human factors ) ) ) ) ) level ) ) ) )
(ROOT (S (NP (PRP they)) (VP (MD might) (VP (VB be) (ADJP (PRN (CC but) (ADVP (RB not) (IN at) (RB not)) (PP (IN at) (NP (DT the) (JJ human) (NNS factors)))) (JJ level))))))
They're not at the human factors level. 
( They ( ( ( 're not ) ( at ( the ( human ( factors level ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP 're) (RB not) (PP (IN at) (NP (DT the) (JJ human) (NNS factors) (NN level)))) (. .)))