Title from PDF file caption (viewed Nov. 14, 2008).
Mode of access: Internet at the FAA web site. Address as of 11/14/08: http://www.airweb.faa.gov/Regulatory%5Fand%5FGuidance%5FLibrary/rgAdvisoryCircular.nsf/0/e20d54750c6ab76586256f320049b44f/$FILE/AC23-21.pdf; current access available via PURL.