Notes data listed below are preliminary. Flight hours and departures are compiled and estimated by the Federal Aviation Administration (FAA). On-Demand Part 135 and General Aviation flight hours are estimated by the FAA's General Aviation and Air Taxi Activity and Avionics (GAATAA) Survey. This survey is conducted and made available in the year following the target year, but is not available at the time when NTSB prepares these annual summary statistics. 

For the purposes of these data, the FAA provides a preliminary estimate of flight activity based on previous year's survey data and trends in tower counts. Departure information for On-Demand Part 135 operations and general aviation is not available. Accidents and fatalities in the categories do not necessarily sum to the figures in U.S. civil aviation because of collisions involving aircraft in different categories.                     

U.S. air carriers operating under 14 CFR Part 135 were as previously referred to as Scheduled and Nonscheduled Services. Current tables now refer to these same air carriers as Commuter Operations and On-Demand Operations, respectively, in order to be consistent with definitions in 14 CFR 119.3 and terminology used in 14 CFR 135.1. On-Demand Part 135 operations encompass charters, air taxis, air tours, or medical services (when a patient is on board).