[Federal Register Volume 64, Number 239 (Tuesday, December 14, 1999)] [Notices] [Pages 69812-69813] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 99-32481] ----------------------------------------------------------------------- DEPARTMENT OF TRANSPORTATION Federal Aviation Administration Draft Advisory Circular (AC) 91-XX, Altimeter Errors At Cold Temperatures AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Notice of availability and request for comments. ----------------------------------------------------------------------- [[Page 69813]] SUMMARY: This notice announces the availability of and request for comments on proposed AC 91-XX, which provides information and pilot/ controller guidance about a potentially hazardous situation with altimeters that occurs at extreme temperatures. Now that international standards have matured to a level of confidence, it is important that cold temperature correction procedures be implemented in the national airspace system. This action is being taken to address Controlled Flight Into Terrain (CFIT) issues and support the Administrator's safety agenda. DATES: Comments must be received on or before January 28, 2000. ADDRESSES: Send all comments on the proposed AC to: Howard Swancy, Flight Procedures Standards Branch (AFS-420), Federal Aviation Administration, 800 Independence Avenue, SW., Washington, DC 20591; telephone number: (202) 267-8724. FOR FURTHER INFORMATION CONTACT: Howard Swancy, Flight Procedures Standards Branch (AFS-420), Federal Aviation Administration, 800 Independence Avenue, SW., Washington, DC 20591; telephone number: (202) 267-8724. SUPPLEMENTARY INFORMATION: Comments Invited A copy of the draft AC may be obtained by accessing the FAA's webpage at http://www.faa.gov/avr/arm/nprm/nprm.htm. Interested parties are invited to submit comments on the proposed AC. Commenters must identify AC 91-XX, and submit comments to the address specified above. All communications received on or before the closing date for comments will be considered by the FAA before issuing the final AC. Discussion The effect of cold temperature on altimeters has been the subject of intense study and analysis since the early days of aviation. These study results indicate that a number of aircraft accidents can be attributed solely to pilot failures to set or use the altimeter correctly. Although, there have been no accidents occurring in the Unites States being directly related to a cold altimeter error, studies confirm a number of near tragic events being thwarted in the final seconds. Cold temperatures tend to induce altimeter error that, in turn, could potentially pose a deadly threat to today's aviators worldwide. At extreme temperatures, altimeters may give pilots significantly erroneous readings. The situation is especially dangerous at cold extremes because altimeters may indicate altitudes higher than the aircraft's actual altitude. This error might be as much as 1000 feet or more. A pilot may not maintain an altitude necessary to clear obstructions when relying solely on the altimeter reading and flying in extreme cold temperatures. The subject of cold temperature altimeter errors has been studied, by world experts, and is considered to be a primary factor facilitating CFIT mishaps. In the interest of safety, every pilot must understand and know procedures to make altitude adjustments as appropriate for actual flight conditions. Issued in Washington, DC, on December 9, 1999. L. Nicholas Lacey, Director, Flight Standards Service. [FR Doc. 99-32481 Filed 12-13-99; 8:45 am] BILLING CODE 4910-13-M