Which combination of conditions produces the highest density altitude at a given airport?
- High temperature, high humidity and low pressure
- Low temperature, low humidity and high pressure
- High temperature, low humidity and high pressure
- Low temperature, high humidity and low pressure
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A. High temperature, high humidity and low pressure
Air is least dense when it is hot, moist and at low pressure. Humid air is lighter than dry air because water vapor weighs less than the air it displaces, which surprises many students.
Reference: FAA-H-8083-25 (PHAK), Chapter 11
An airport's elevation is 2,400 feet and the altimeter setting is 29.42 in. Hg. Using 1,000 feet per inch of mercury, what is the pressure altitude?
Answer in feet.
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2900 feet
Difference from standard = 29.92 - 29.42 = 0.50 in. Hg = 500 feet. The setting is below standard, so add: 2,400 + 500 = 2,900 feet.
Reference: FAA-H-8083-25 (PHAK), Chapter 11
An airport's elevation is 1,150 feet and the altimeter setting is 30.32 in. Hg. Using 1,000 feet per inch of mercury, what is the pressure altitude?
Answer in feet.
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750 feet
Difference from standard = 29.92 - 30.32 = -0.40 in. Hg = -400 feet. The setting is above standard, so subtract: 1,150 - 400 = 750 feet.
Reference: FAA-H-8083-25 (PHAK), Chapter 11