People watching a low airplane flying overhead
The people are at an airport.
Airplanes may fly low at any location, not just at an airport.
exists e1 e2 s1 x1 x2 x3 x4 x5.(a_topic(x1) & Theme(e2,x3) & Actor(e2,x2) & v_watch(e2) & Theme(e1,x5) & Actor(e1,x4) & v_fly(e1) & n_overhead(x5) & (x3 = x4) & n_airplane(x3) & a_low(s1) & Theme(s1,x3) & (x1 = x2) & n_people(x1))
exists p1 x1.(n_people(x1) & exists x2.(at(x1,x2) & n_airport(x2)))