For more information, please see the Import/Export Price Indexes frequently asked questions site at http://www.bls.gov/mxp/fact_sheets.htm.
Source: US. Bureau of Labor Statistics
Release: U.S. Import and Export Price Indexes
US. Bureau of Labor Statistics, Services Outbound Index: Outbound Air Freight [IS231], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/IS231/, August 30, 2015.