Chapter 3 - Pressure Flashcards
Why are we interested in Px
Because A/C can base their height on it, to aid with traffic and terrain avoidance
How do we measure Px on the ground
Mercury barometer using formula P = Force/Area
How do we measure Px on A/C
Using a simple Aneroid Barometer
Air moves because of
Px differences
Elongated bars are called what for High and Low Px
Ridge/wedge
Troughs
In the northern hemisphere which way does the wind move round high and low Px
Clockwise round Hpx
Anti clockwise round Lpx
Low Px air is moving how
Convergent - asending air - adiabatic cooling
High Px air is moving how
Diverging - descending air - adiabatic warming
Describe the effect of temperature on Px in column of air
colder it will over read for the true height - a/c believes to be higher than actual
warmer it will under read for the true height - a/c believes to be lower than actual
constant pressure charts can be display what and are measured in
Isohypes (Contour) lines of equal Px above the surface
Metres x 10 = decometres/DAMS
Which air falls more quickly out of hot and cold
cold
What does QFE =
Field Elevation - usually measure accurately
What does QNH =
Nautical Height - calculated using QFE - ISA Lapse rate
What does QFF =
calculated using QFE - actual pressure lapse rate for the day
What does SPS =
Standard Pressure Setting = 1013.25H Pa Mainly used in commercial a/c
What is the Lapse rate of pressure
27 ft / H Pa - 8 m / H Pa
What are regional pressure settings? (RPS)
When flying below transition altitude, pilots can use RPS which is valid for an hour in that region
If you wind on Px on the Altimeter
It increases the indicated height
How is Transition Altitude calculated? And what do we do?
It is published
Swap to SPS
How do we calculate Transition Level? And what do we do?
It is calculated for that day.
Swap to QNH
What happens in Cold to Warm air
Indicated Altitude will be higher = safer
What happens to Warm to Cold air
Indicated Altitude will be lower = dangerous
what is the calculation for working out temp correction
for every 10 degrees - apply 4%
Temp calculation only applies where?
Air is
Valleys do what to altimeters?
convergent duct so Px goes down so altimeter will read higher
