▁vest ib ular ▁system ▁are ▁most ▁likely ▁under ▁conditions ▁with ▁un re li able ▁or ▁un available ▁external ▁visual ▁references . ▁ ▁In version ▁ ▁An ▁ab rupt ▁change ▁from ▁clim b ▁to ▁straight - and - level ▁flight ▁can ▁stim ulate ▁the ▁ot ol ith ▁org ans ▁enough ▁to ▁create ▁the ▁ill usion ▁of ▁t umb ling ▁backwards , ▁or ▁in version ▁ill usion . ▁The ▁dis orient ed ▁pilot ▁may ▁push ▁the ▁aircraft ▁ab rupt ly ▁into ▁a ▁nose - low ▁attitude , ▁possibly ▁intens ifying ▁this ▁ill usion . ▁ ▁Head - up ▁ ▁The ▁head - up ▁ill usion ▁involves ▁a ▁sudden ▁forward ▁linear ▁acceleration ▁during ▁level ▁flight ▁where ▁the ▁pilot ▁perce ives ▁the ▁ill usion ▁that ▁the ▁nose ▁of ▁the ▁aircraft ▁is ▁pitch ing ▁up . ▁The ▁pilot ' s ▁response ▁to ▁this ▁ill usion ▁would ▁be ▁to ▁push ▁the ▁y oke ▁or ▁the ▁stick ▁forward ▁to ▁pitch ▁the ▁nose ▁of ▁the ▁aircraft ▁down . ▁A ▁night ▁take - off ▁from ▁a ▁well - lit ▁air port ▁into ▁a ▁totally ▁dark ▁sky ▁( black ▁hole ) ▁or ▁a ▁cat ap ult ▁take - off ▁from ▁an ▁aircraft ▁car rier ▁can ▁also ▁lead ▁to ▁this ▁ill usion , ▁and ▁could ▁result ▁in ▁a ▁crash . ▁ ▁Head - down ▁ ▁The ▁head - down ▁ill usion ▁involves ▁a ▁sudden ▁linear ▁dec eler ation ▁( air ▁bra king , ▁lower ing ▁f laps , ▁decre asing ▁engine ▁power ) ▁during ▁level ▁flight ▁where ▁the ▁pilot ▁perce ives ▁the ▁ill usion