Flashcards in Pressure Deck (47)
The atmosphere is composed of a variety of gases these are....
Carbon Dioxide (0.04%)
What is atmospheric pressure defined as?
Combined weight of gases exerting force in all directions
What is used to measure atmospheric pressure?
What is pressure expressed as?
Inches or Millibars of Mercury
A hectopascal is equal to...
100 newtons per square metre
What is an isobar?
The line on the map to indicate locations of the same pressure
What happens to pressure as you increase altitude?
What is the ISA pressure at sea level?
In HPA, Hg and lb/sq.in
What is QNE (Question Nil Elevation)?
Setting 1013 on aircraft subscale
QNE is a pressure setting of 29.92 inches or 1013 hPa that will produce a standard atmosphere altitude and provides the basis for flight levels.
With QNE set on the altimeter, the main scale will indicate?
Height above or below 1013 HPA Pressure level
(Pressure height or Pressure Altitude)
At low level, the pressure reduces at a rate of...
1 HPA / 30ft of altitude increase in the troposphere
=1 Hg / 1000ft
Air density refers to....
Mass of air occupying a given volume
What 3 factors does air density depend on?
Decreased Pressure= .... Density
Does high density give better or worse aircraft performance?
Why do variations in pressure occur?
- The movement of pressure systems
- Changing the intensity of pressure systems
- Semi diurnal Pressure variation
What is semi-diurnal variation?
Rhythmic variation in pressure over 12 hour period
Where is semi-diurnal variation the greatest?
Can change up to 5 HPA
What is standard pressure?
What is the actual mean sea level pressure referred to as?
When QNH is set on altimeter it will read...
Altitude (Height above mean sea level)
What is local QNH?
Actual sea level pressure for a particular location
Where is Local QNH available?
Control tower or ATIS
If you set the airfield elevation on your altimeter what will it read?
Approx. Local QNH
What is area QNH?
Predicted average sea level pressure
Who forecasts area QNH?
Bureau of Meteorology
How often is area QNH updated?
Every 3 hours