Altimetry Flashcards
What is altimetry?
The determination of our vertical distance from references levels.
What is QFE? What do we get if we set QFE on the subscale?
QFE is the pressure reading taken at the aerodrome/landing location.
Using the QFE will give us the HEIGHT above the aerodrome.
What is QNH? What do we get when setting QNH in the subscale?
QNH is a derived pressure for the mean sea level. Calculated using the QFE - (elevation/27.
Using QNH gives us our ALTITUDE Above MSL.
What is QNE/SPS? What do we get if we use this in the subscale?
QNE is a standard pressure setting used universally in accordance with the ISA. Setting 1013hPa.
QNE gives us our pressure altitude and FLIGHT LEVEL. Based on ISA.
QNE does not factor in temperature variations from ISA.
We use QNE as our altimeters are calibrated to the standard ISA.
What is QFF?
QFF is derived from QFE as the actual pressure at sea level by factoring in temperature deviation from ISA.
basically QNH with temperature correction.
Used by meteorologists to create weather charts.
What happens at the transition altitude?
we switch settings from QNH to 1013 standard.
The transition altitude is always published.
What happens at the transition level?
We switch settings from 1013 standard to QNH for our approach.
The transition level is subject to change due to changes in QNH
What is the transition layer? How is it calculated?
the airspace between the transition ALT/LVL.
Calculate the difference between indicated altitude and true altitude.
if subscale is not changed, what happens when moving to a lower pressure area?
the ALT will over-read. (if maintaining alititude then plane will decent to maintain previous set level) this can be dangerous for terrain clearance
If subscale not changed, what happens when moving to a higher pressure area?
the ALT will under-read. (if maintaining altitude then plane will climb to previous set level)
when changing subscale to a lower pressure, what will happen to the reading?
The indicated altitude will decrease. (the needle will read a lower alt) becuase the distance between altimeter and reference level is decreasing.
When changing subscale to a higher pressure, what will happen to the reading?
The indicated altitude will increase. Becuase the distance between altimeter and reference level is increasing.
How do we calculate true altitude?
edit
How do we calculate QFF?
mass of elevation ‘column’ between seal level and QFE. affected by temperature.
Colder air is dense and warmer air less dense. means QFF will be greater than QNH when colder and vice versa. Reversed when QFE is below sea level.
