Based on the leaked video, the first word that came to mind was "linebacker" (for those behind)... that guy was totally focused on what was in front of him... looked like a good opportunity for a strip-sack for an aware person behind him. However, my first commitment is do what is necessary to protect my family, which includes surviving to continue to provide for them, since they don't need direct protection from this immediate threat.
So, realistically, probably run like hell... Second choice is to dive for cover. Whatever seems like it will give the best opportunity of survival at the time. Hard to say without being in the moment...
Let those who volunteer and get paid to deal with such situations (they are there to protect me, since the governments for whom they work decided I should be defenseless, right?) take care of the bad guy.
Along those lines, here's a perspective most likely haven't seen expressed very widely, if at all: https://www.lewrockwell.com/lrc-blog/cops-form-perimeter-mass-murderer-goes-business/
Personally, I'm a fan of breaking the bystander effect. Im there, and the cops arent. If I had been in that chair instead of the old man and saw him walking away from me popping off shots oblivious to his 6, damn right I'm going linebacker. Cops that are minutes away?
I'd be doing the fastest and quietest sprint I could do. I'm no hero. If it were somebody not so focused on moving away from me and oblivious I would duck and cover first to reset the OODA loop. Not gonna lie. But I'm sick of the lay down and wait sheeple mentality.
As to the perimeter failure, this has been an issue since Columbine, but I know many departments are working to fix it by authorizing officers to team up and penetrate and start the sweep asap while their brothers setup the perimeter as they arrive to fill the hole the heroes leave as they head into the belly of the beast. I couldnt do it, thank you for those of you that do. You are appreciated.
Though I wonder how much psychological factor the airport property had on this. I could easily see "crap! This could be a large terrorist attack. Do we have the manpower to go? Should we wait for SWAT so we arent outgunned by Achmed?" (fog of war and all)