( ( ( ( ( A decrease ) ( in density ) ) ( of ( ( air results ) ( in decrease ) ) ) ) ( in ( both ( aircraft ( and ( Engine performance ) ) ) ) ) ) . )
(ROOT (NP (NP (DT A) (NN decrease)) (PP (IN in) (NP (NN density))) (PP (IN of) (NP (NP (NN air) (NNS results)) (PP (IN in) (NP (NN decrease))))) (PP (IN in) (NP (DT both) (NN aircraft) (CC and) (NN Engine) (NN performance))) (. .)))
A decrease in density of air results in decrease in both aircraft and Engine performance.
(ROOT (S (SBAR (IN As) (S (NP (DT the) (NN altitude)) (VP (VBZ decreases)))) (, ,) (NP (NP (DT the) (NN density)) (PP (IN of) (NP (NN air)))) (VP (VBZ decreases)) (. .)))