For further information, please refer to the US Census Bureau's Annual Services release, online at http://www.census.gov/services/.
Source: US. Bureau of the Census
Release: Annual Services Survey
US. Bureau of the Census, Total Expense for Nonscheduled Chartered Freight Air Transportation, Establishments Subject To Federal Income Tax, Employer Firms [EXPEF481212TAXABL], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/EXPEF481212TAXABL/, August 29, 2015.