I have absolutely no idea!
I set up the mission to be a simple intercept of the Airbus (actually the 'real' mission was to intercept a Tu-95 on a recon run off the North Sea coast but I set up a couple of F-15Cs out of Lakenheath to take care of that). The story was that the airliner's navigation equipment had gone down and we would form up on it and lead it down through the clouds and onto the runway.
I was as surprised as anyone when I got in visual range, and the flyby to check over the airliner was real. I re-wrote the story in my head on the fly as I tracked the Airbus down and over London until it landed.
Funny thing is I've flown the mission a few more times since then because I thought I had set something wrong, maybe with the airliner dropping below stall speed, and it has been absolutely fine...
Maybe TK programmed in a secret setting - RandomCatastrophicMishap=TRUE