Actually it is almost exactly 1 in 1000.
The aircraft will be within plus or minus 100 ft both vertically and laterally. That is 40,000 square feet. The engine has an area of about 20 square feet. Two engines equal 40 square feet. If the UAV doesn’t move, the random odds of hitting an engine is 1/1000. I just did the math for fun.
Cubic feet three dimension. Add time and reality since a perfectly unmoving UAV isn’t reality.