Cold Weather Altitude Correction is a tool for calculating temperature corrected altitudes.
Conventional tools are only calculating a list of altitudes. This tool is designed more closely to a real approach. It is showing the corrected altitudes in a graphical interface:
Corrected values are always blue. With only temperature and elevation you can move the yellow dot along a vertical profile to show the corrected value for any desired altitude .
In addition you may enter values for MSA, DA/MDA and GPA to calculate their corrected values and have a visual impression of the approach.
An additional altitude, distance to threshold or DME value may be displayed as green line and/or a green dot on the profile.
But the real sophisticated part is the Distance - Altitude Table:
A table with distances and corrected altitudes will be calculated.
The distances may be distances to threshold or distances to a user defined DME station. The DME station must be on or close to the centerline.
Calculation Methods
According ICAO PANS OPS Doc 8168 Volume I Part III. Section 1. Chapter 4.3 Temperature corrections, 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 settings for temperatures above -15°C.
For temperatures of -15°C and below a more accurate correction should be obtained from a given equation, producing results that are within 5 per cent of the accurate correction for altimeter setting sources up to 3.000 m (10.000 ft) and with minimum heights up to 1.500 m (5.000 ft) above that source.
Both methods provide margins to the accurate correction, but the margin of the standard altitude correction of 4% will decrease with falling temperature. Both are based on the ICAO standard atmosphere with a linear temperature profile, but the real atmosphere may have a different temperature profile.
The app is using the mentioned equation recommended for temperatures of -15°C or below for all calculations.
Accuracy
The displayed values are not an exact reflection of the reality.
Horizontal and vertical resolution are quite different:
Horizontal 0.1 nm, vertical 10 ft.
At 3° GPA ± 0.1 nm equals to ± 32 ft.
That results in a vertical accuracy of ± 20 ft.
