Electronic reproduction. [Washington, D.C.] : Federal Aviation Administration, [1966] Mode of access: World Wide Web. System requirements: PDF reader.
Mode of access: Internet at the FAA web site. Address as of 3/5/09: http://www.airweb.faa.gov/Regulatory%5Fand%5FGuidance%5FLibrary/rgAdvisoryCircular.nsf/0/48617be49343eea1862569bc0057d246/$FILE/ac121-6.pdf; current access available via PURL.