KEY: N = data are nonexistent; NPIAS = National Plan of Integrated Airport Systems.
NOTES: See box 2-B on the facing page for definitions of NPIAS and commercial service airports. NPIAS airports data include commercial service airports.
SOURCES: 1997–2003—U.S. Department of Transportation (USDOT), Research and Innovative Technology Administration, Bureau of Transportation Statistics, National Transportation Statistics 2004, table 1-24, available at http://www.bts.gov/, as of January 2005. 2004—USDOT, Federal Aviation Administration, National Planning Division, personal communication, February 2005.