Federal Aviation Regulations Title 14, Chapter I, Subchapter E, §71.31, §71.33
faa.gov
faa.gov
"Instrument Flying Handbook"(PDF), Instrument Flight Rules (defined), Oklahoma City, Oklahoma: Federal Aviation Administration, 2008, pp. G–9
"Aeronautical Information Manual"(PDF), Instrument Flight Rules (defined), Oklahoma City, Oklahoma: Federal Aviation Administration, 11 February 2010, pp. PCG I−4
Keel, Byron; Stancil, Charles; Eckert, Clifford; Brown, Susan (June 2000). "Aviation Weather Information Requirements Recommendations". Aviation Weather Information Requirements Study. Hampton, Virginia: NASA Langley Research Center. pp. 40–41. CiteSeerX10.1.1.32.1842. {{cite book}}: |work= ignored (help)