mandag 13. januar 2020

Temperatur korreksjon av barometriske høydemålere - Eurocontrol

I samme slengen burde en tatt med vindkorreksjon av MSA enroute. CFD (Computational Fluid Dynamics) Norway, Report 109.1989. (Red.)

Welcome to the January 2020 edition of SKYlight - "Safety Intelligence as a Service". This is a month of global contrast as we see extreme temperature events in both the Northern and Southern hemispheres, with record high temperatures in Australia and predictions of a polar vortex event in North America. This month we take a look at temperature error correction - something which continues to be a contributory factor in CFIT events. We also have several new articles prepared by members of our editorial team.

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Altimeter Temperature Error Correction

What is Altimeter Temperature Error
Altimeter Temperature Error Correction is applied to altimeters to compensate for error caused by deviation from ISA conditions. Pressure altimeters are calibrated to ISA conditions. Any deviation from ISA will result in error proportional to ISA deviation and to the height of the aircraft above the aerodrome pressure datum. According to ICAO PANS OPS (Doc 8168) "The calculated minimum safe altitudes/heights must be adjusted when the ambient temperature on the surface is much lower than that predicted by the standard atmosphere. In such conditions, an approximate correction is 4 per cent height increase for every 10°C below standard temperature as measured at the altimeter setting source. This is safe for all altimeter setting source altitudes for temperatures above –15°C. For colder temperatures, a more accurate correction should be obtained according to the guidance provided in section 4.3 "Temperature corrections". When temperature is LESS than ISA an aircraft will be LOWER than the altimeter reading. For example, if the OAT is - 40 °C then for a 2000 ft indicated altitude the true altitude is 1520 ft thus resulting in a lower than anticipated terrain separation and a potential obstacle-clearance hazard.

When To Apply Corrections
When the aerodrome temperature is 0°C or colder, the temperature error correction must be added to:

DH/DA or MDH/MDA and step-down fixes inside the final approach fix (FAF).
All low altitude approach procedure altitudes in mountainous regions (terrain of 3000 ft AMSL or higher)

According to ICAO PANS OPS Chapter 4 "Altimeter Corrections", the pilot-in-command is responsible for the safety of the operation and the safety of the aeroplane and of all persons on board during flight time (Annex 6, 4.5.1). This includes responsibility for obstacle clearance, except when an IFR flight is being vectored by ATC. When pilots intend to apply corrections to the FAF crossing altitude, procedure turn or missed approach altitude, they must advise ATC of their intention and the correction to be applied. Pilots may refuse IFR assigned altitudes if altitmeter temperature error will reduce obstacle clearance below acceptable minima. However, once an assigned altitude has been accepted, it must not subsequently be adjusted to compensate for temperature error.