39 Air Data Measurement

Question 1

CAO Standard Atmosphere

Answer 1

Pressure:
29.92 in HG / 1013.25mb at Mean Sea Level

Temperature:
15ºC at MSL

Lapse Rate:
Atmosphere cools at a rate of 2ºC per 1000ft

Pressure change:
1mb pressure drop = 30 ft
1 inch Hg pressure drop = 1000ft

Question 2

Pressures
Static (P)
Dynamic (Q)
Pitot (H)

Answer 2

Static Pressure (P)
The atmospheric pressure a the aircraft altitude unaffected by the motion of the aircraft
A given static pressure corresponds to a specific altitude in the ISA
Actual static pressure depends on air temperature and density
Dynamic Pressure (q)
The pressure which is due to the motion of the aircraft
It increases with increased speed
Also called differential or ram pressure
Pitot pressure (H)
PITOT or TOTAL pressure is a measure of P + q