The meltdown of airline transportation in the Northeastern US caused by the New York and Boston airport closures during the December 26-27th blizzard, and the cancellation of over 10,000 flights, is a prime example of propagating failures. Occurring during the peak travel season of the year, it seemed as if the stars aligned for the worst possible scenario. We are now hearing that it will take almost another week until all the passengers originally scheduled to fly during that period will arrive at their destinations (lucky are those who were able to opt for other modes of transportation, where available and feasible).
In trying to determine the causes, and the possible solutions for the future, this natural event, in the form of a blizzard, happened at what was to be the peak travel week. With Christmas and New Year's Day both occurring on Saturdays in 2010, thus allowing many to take December 24th off, many traveled for the holiday. On the 26th , travelers were either scheduled to return home or to begin a post Christmas vacation, with plans to return to their destinations by January 2nd. Because of such timings of these holidays, the load factor for flights was already sky high.
While the weather was the cause that ultimately brought the system to a standstill, the root causes that led to this failure are really decisions made by the airline industry which were ultimately driven by the economy. With the uncertainty in today's economy, airlines have cut their schedules to the bare minimum. Thus, while capacity is consistent with demand, under normal circumstances, and the best scenario, a shock caused the sudden change in capacity which could not be absorbed by the airline system. Moreover, demands got altered at various nodes as people tried to rebook.
Horrific “survival” stories abounded (and continue in this prolonged nightmare) with passengers on five Cathay Pacific flights being kept on the tarmac at JFK airport from 4 to 11 hours and this was after their already lengthy flights!
Moreover, for those trapped in airports, since the number of airline call centers have been cut, also due to economic pressures, many passengers with hopes of rebooking spent hours dialing and redialing at airports, only to be cut-off, whereas a human at the other end may have been able to assist. Even the Internet was not that helpful, since most airline websites have only limited rebooking capabilities. Of course, the airlines do not cancel reservations of those who booked early, so, for example, someone who had a confirmed reservation to fly out of Boston today will have his/her seat today, while someone who had a reservation on the same flight on Monday might still be waiting to be rebooked (and transported).
This blizzard (with the 6th worst recorded snowfall in NYC history) also disrupted train travel and even stopped subways in NYC with passengers being trapped for upwards of 8 hours (and even being treated afterwards for frost-bite). It also affected emergency vehicle transport with numerous ambulances stuck.
In a recent paper of ours, "A Bi-Criteria Measure to Assess Supply Chain Network Performance for Critical Needs Under Demand and Capacity Disruptions," we developed a model of network performance under capacity and demand disruptions. Also, a recent study of ours, "Fragile Networks: Identifying Vulnerabilities and Synergies in an Uncertain Age," provides even measures for robustness of transportation networks (clearly, robustness was severely lacking this past week in the Northeast in our airline infrastructure). I hope that transportation officials and airlines will pay attention to the research.
Personally, our travel plans to NYC were also disrupted by the blizzard as were those of friends' who were hoping to fly in so that we could reconnect.
The timing of the Transportation Research Board panel on Disaster Recovery and Mitigation Planning and Resilience next month could not be better timed.