AoG Emergencies happen all the time, here is just one recent example.
London Gatwick Airport and a Jumbo jet has a component failure whilst the ground handling team are doing the turn around checks. At the gate very shortly will be several hundred passengers. The cost implications of a delayed or cancelled flight can be horrendous and so a courier was despatched to a large aircraft spares company at Hurn Airport to collect the replacement part. The courier made good time, the passengers had only a short wait whilst the engineers fitted the part and the plane continued safely to it's destination.