Standard atmosphere - Answers Sea level temp + 15 degrees C (59 degrees F)
29.92 Hg (atmospheric pressure) or 1013 mb
0% Relative Humidity
Pressure altitude - Answers The height above the standard datum plane (SPD is theoretical level at
which the pressure of the atmosphere is 29.93 Hg and weight of air is 14.7 psi)
Important as a basis for determining aircraft performance and assigning for levels to aircraft operating at
or > 18000 ft
Can be determined by
1.) setting the barometric scale of the altimeter to 29.92 Hg and reading indicated alt
2. Applying a correction factor to the indicated altitude according to the reported "altimeter setting"
3. By using a flight computer
Density altitude - Answers Pressure altitude corrected for variation from standard temperature
Deviation from standard change density altitude
When temp is > standard. DA > PA
When temp is < standard, DA < PA
, As air density decreases (Higher density altitude) aircraft performance decreases- thin air - result of high
elevations, low atmospheric pressures; high temps, high humidity, or combo
As density of air increases (lower density altitude) aircraft performance increases - dense air-result of
low elevations, high atmospheric pressure, low temps, low humidity
Vertical distance above sea level in the standard atmosphere at which a given density is to be found
Effects of humidity (moisture) on densiry - Answers Water vapor is lighter than air; moist air lighter than
dry air, as water content increases, air becomes less dense, increasing DA and reducing performance
Humidity refers to amount of water vapor contained in atmosphere and is expressed as a percentage of
the max amount of water vapor air can hold- amount varies with temp- warm air holds more water
vapor and cold air holds less
Expect a decrease in overall performance on high humidity conditions
Density altitude factors - Answers Humidity- increase in humidity raises the density altitude effects
Altitude - air has reduced density at higher alt
Temperature - increase or decrease in temp increases or decreases DA respectively
Decreasing air density = higher density altitude
Primary responsible for aircraft performance
As air becomes less dense it reduces - Answers Power- engine takes in less air
Thrust- propellor less efficient in thin air