In the U.S., airline schedules are challenging even on good weather days. When bad weather limits the capacities of airports and airspace, U.S. Federal Aviation Administration (FAA) Traffic Flow Management (TFM) specialists at the Air Traffic Control System Command Center (ATCSCC) may institute various TFM initiatives to manage excess demand. These actions are undertaken as part of a collaborative decision-making (CDM) process involving the FAA and major airlines. FAA TFM actions can be divided into strategic actions, which are typically taken at least 2 hours before weather is expected to affect operations and tactical actions, which are taken within 2 hours of weather. Strategic TFM actions include ground delay programs (GDPs), which reduce the demand to a given airport by spreading out the original schedule over time, and playbook actions, which reroute large blocks of traffic around regions of en-route airspace according to predefined plans. Tactical TFM actions include ground stops (GSs), which stop flight on the ground that are due to arrive later at given airport, coded departure routes (CDRs), which reroutes specific flights from a given airport, and reroutes around the weather. In addition, airlines may respond to weather or forecast weather with flight cancellations and, if necessary, diversions. Strategic TFM decision making may take place in the context of significant uncertainty with respect to both demand and weather information. With the advent of CDM, there has been an overall improvement in the extent and quality of information exchanged regarding departure times and cancellations.2. As a type of TFM actions, tactical actions are taken（ ）.