[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]


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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.

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[[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