I've managed to force it again, but only once, and I'm unsure of what the conditions were, because what I tested after I ran into it again (trying to get interceptors to run low on fuel as research completed) never caused it to occur again. I'm not even sure how I managed to get the interceptor to engage the UFO in my original post, because I distinctively remember the buttons being disabled after it ran out of operational fuel. I'll keep trying to see if I have better luck.