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Meeting	ACGS Committee Meeting 93 - Colorado Springs - March 2004
Agenda Location	7 SUBCOMMITTEE C – AVIONICS AND SYSTEM INTEGRATION 7.3 Cold Temperature Effects on Barometric VNAV Performance and Automatic Temperature Compensation
Title	Cold Temperature Effects on Barometric VNAV Performance and Automatic Temperature Compensation
Presenter	Barry Billmann and Lt Col Kris Fortmann
Affiliation	FAA William J. Hughes Technical Center
Available Downloads*	presentation
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Abstract	The Navigation Aids and Avionics Group at the William J. Hughes Technical Center, in Atlantic City, New Jersey, conducted a series of flight tests to quantify the cold temperature effects on barometric VNAV performance. The testing was conducted at Bangor, Maine and Yellowknife, NWT, Canada. The objectives of the testing was to validate entries in the altitude correction tables found in the Aeronautical Information Manual (AIM) and ICAO’s Procedures for Air Navigation Services-Operations, and to quantify the performance of one method of automatic temperature compensation on the final segment of a barometric VNAV procedure. A total of 187 barometric VNAV approaches were flown in temperatures ranging from the international atmospheric standard (ISA) –10oC to ISA -53oC. Test results showed that the tabled altitude correction values were conservative. On the average, automatic temperature compensation worked quite well. However, at these cold temperatures, extreme departures from the standard lapse rate were not infrequent. Some deep inversions were observed which resulted in an over compensation of the altitude error resulting in glide path steeping that increased the glide path angle by more than 12% in some cases. Some operational issues, associated with automatic temperature compensation were also observed during testing.