This is a good example of what is possible with low cost and low risk systems disruption. Some additional thinking:
Cost of drones: ~ $100. Disruption value: ~$40-60 million (110,000 x $400 per ticket). ROI = $500,000 for every $ invested
Method of attack: simple runway/terminal overflights. Easiest to plan/accomplish.
Timing of overflights maximized impact. Initial flurry of overflights demonstrated it was a serious threat. Infrequent but constant overflights showed the threat was still present. No rapid return to business as usual possible.