101-3 Pressure & Altimetry Flashcards
Two types of barometers
- Mercurial
- Aneroid
QFE
Station Pressure
Actual pressure @ field elevation or wx station
QNH
Altimeter Setting
Sea-level pressure value to which the scale of the altitude is set
Pressure Variation
Pressure lapse rate is 1” hg / 1000’
Only up to 10K, slows past that point
Pressure drops faster in cold air (i.e. faster than 1”/1000’
True Altitude
(TA)
actual altitude above MSL
I.e. Field elevation of airport
Absolute Altitude
Actual altitude above terrain
Indicated altitude
Altitude above MSL as indicated on the altimeter when using the local altimeter setting (below 18,000)
Altimetry Rule 1
When flying HIGH to LOW = Look out below
*the aircraft is lower than the altimeter says
TA < IA
Altimetry Rule 2
When flying LOW to HIGH = reach for the sky
*aircraft is higher than altimeter says
TA > IA
Flying at 14000 @ 29.72
Land at airport w/ elevation of 3000’ @ 29.52 (QNH)
What is IA after landing?
3200 IA
DA relation to PA
- If the atmosphere is warmer than std = DA > PA
-if the atmosphere is colder than std = DA < PA
Pressure Altitude
Altitude indicated on the altimeter when using 29.92” hg as the setting
Density Altitude
Pressure altitude corrected for non-standard temperature
Characteristics of High Density Altitude
Low air density
Decreased performance
Decreased climb rate
Increased take off roll/ray
*Less Dense
*found at high elevation airports
*not good
*High Temp & Low Pressure
Characteristics of Low Density Altitude
High Air density (more dense)
Increased performance
Increased climb rate
Decreased take off roll/RWG
*Low temp + High Pressure
Isobars
Lines of equal pressure (surface wx charts)
Isotachs
Lines of equal wind speed (aloft chart)
Isotherm
Line of equal temp (aloft charts)
Contour
Line of equal height (aloft)
Wind flows parallel to contours
Wind speed increases as contour line spacing decreases
Low pressure systems
Center of pressure surrounded by relatively higher pressure
*associated w/ poor weather (tropical storm or blizzard)
Counterclockwise
Inward and upward
Trough
(TROF)
Elongation of low pressure area
*turbulent
High pressure system
Center of pressure surrounded by low pressure
*better weather
Clockwise winds
Outward and downward
Ridge
Elongation of high pressure areas
*turbulent
Departs w/ 29.60”
Elevation of landing airport 3000’ @ 30.10
What is the IA?
2500
How to calculate pressure altitude
Ex. 500’ elevation airport w/ current altimeter setting of 29.62
29.92 - 29.62 (atl. Setting at airport) = .30
.30 x 1000 = +300 adjustment
500 + 300 = 800 PA
