A helicopter is flying behind a plane that is performing aerobatics.
A helicopter is standing by in case the plane's pilot messes up.
Just because a helicopter is flying behind a plane that is performing aerobatics does not mean that it  is standing by in case the plane's pilot messes up.
exists e2 e1 x1 x2 x3 x4.(behind(e1,x2) & Theme(e2,x4) & Actor(e2,x3) & v_perform(e2) & n_aerobatics(x4) & (x2 = x3) & n_plane(x2) & Actor(e1,x1) & v_fly(e1) & n_helicopter(x1))
exists e1 p1 s1 x1 x2 x3 x4.(n_pilot(x4) & of(x4,x3) & n_plane(x3) & in(e1,x2) & exists e2 s2.(a_up(s2) & Manner(e2,s2) & Actor(e2,x4) & v_mess(e2)) & that(x2,p1) & n_case(x2) & a_by(s1) & Manner(e1,s1) & Actor(e1,x1) & v_stand(e1) & n_helicopter(x1))