Flying in an air mass 15°C colder than ISA (ISA-15), the altimeter set to the QFE of a nearby aerodrome at elevation 2000 ft indicates 4500 ft, pressure altitude is 5500 ft. What is the true height of the aircraft overhead the aerodrome?
Refer to figure.
Pressure Altitude: The altimeter indication with standard pressure (1013.2 hPa) set.
Indicated Altitude: The altimeter indication with local QNH set (in this case, QFE).
True altitude: The actual altitude of the aircraft above mean sea level.
To calculate the aircraft’s true height, let's consider the indicated altitude (with QFE set) of 4 500 ft.
First, we need to determine the temperature correction. Given an ISA deviation of ISA -15ºC and using the 4% rule, we calculate the height correction for temperature as follows:
- Height correction for temperature = 4 × (-15) × (4 500/1000) = -270 ft.
Since the ISA deviation is negative, the true height will be lower than the indicated altitude. Therefore, we subtract the temperature correction from the indicated altitude according to the rules, resulting in a true height of 4 230 ft (4 500 ft – 270 ft).
Your Notes (not visible to others)
This question has appeared on the real examination, you can find the related countries below.
-
France3
-
Spain2
-
Germany1
-
Sweden1
-
United Kingdom1
Use Keyboard Shortcuts
