Chapter 5: Atmosphere And Speed Flashcards
What is the aviation definition of height ?
Height is the measured distance above the ground ie. QFE
What is the aviation definition of altitude?
Altitude is the measured distance above the local pressure setting (QNH) or altitude above mean sea level
What is the aviation definition of flight level?
Flight level is the measured pressure level about the 1013hPa datum
What does ISA stand for?
International standard atmosphere
What are the ICAO ISA conditions at sea level?
Temp 15 degrees Celsius. Pressure 1013hPa. Density 1225g/m3
What is air pressure?
Air pressure is the weight of a column of air or the gravity force of air molecules. It is influenced by gravity and proportional to density. Air pressure decreases with altitude. Measured in hPa p, force per unit area.
How many feet are in a hectopascal?
It is variable as the rate that pressure changes with height is variable . It is more rapid near the earths surface and less so at higher altitudes. You can use below equation to calculate:
96X(273+actual temperature)/altitude pressure.
It is common to use 30ft per hPa until 5000ft
How many inches of mercury to a hectopascal?
0.0295 inches of mercury
What is pressure altitude?
Pressure altitude is the international standard atmosphere height above the 1013 datum at which the pressure value experienced represents that if the level under consideration
How do you calculate pressure altitudes actual height?
First calculate difference between regional QNH and the 1013hPa datum. Convert the pressure difference into height. Then add or subtract height.
Why do you need to calculate the actual height of a pressure altitude?
A difference between actual mean sea level pressure from the ISA atmosphere will give rise to a difference between pressure altitude and actual altitude.
- Ground clearance
- Calculating performance capabilities of aircraft
What pressure altitude error is commonly experienced?
Barometric pressure error.
This is the effect of flying into an area with a different sea level pressure, giving rise to an incorrect altimeter reading.
High to low beware below.
Describe OAT
OAT is the ambient outside air temperature
Describe SAT?
SAT is the ambient static air temperature. Just a different name for outside air temperature.
Describe TAT?
Total air temperature. Product of the static air temperature SAT and the adiabatic compression (ram) rise in temperature experienced on the temperature probe. TAT will be higher when there is an airflow into the temperature probe. Often referred to as heating error.
