I was stuck in the basement at JFK for two hours because the bar code readers at passport control went down. As more flights arrived it became a crowded sweaty mess. Of course, no phones allowed.
This was shortly after swiping passports became de riguer for returning citizens. The agents were not allowed to process passengers as they had done just the year before. No swipe, no go.
Without an analog backup, electronic systems are a major pita when they go down, as they inevitably will.