If the altimeter setting drops 0.15 inHg, how much will pressure altitude change?

If the altimeter setting drops 0.15 inHg, how much will pressure altitude change?

• A. 30 feet
• B. 75 feet
• C. 150 feet
• D. 300 feet

Answer: (D)

Pressure altitude shifts in direct proportion to changes in the altimeter setting. Roughly, 1 inHg change equals about 1000 ft. A drop in the altimeter setting of 0.15 inHg means the difference (29.92 − QNH) increases by 0.15, so the pressure altitude increases by 0.15 × 1000 ≈ 150 ft. Using PA = Elevation + (29.92 − QNH) × 1000 helps see this: lower QNH (the setting) raises the PA by the corresponding amount. A 0.30 inHg change would give about 300 ft, but a 0.15 inHg change yields about 150 ft.

Pressure altitude shifts in direct proportion to changes in the altimeter setting. Roughly, 1 inHg change equals about 1000 ft. A drop in the altimeter setting of 0.15 inHg means the difference (29.92 − QNH) increases by 0.15, so the pressure altitude increases by 0.15 × 1000 ≈ 150 ft.

Using PA = Elevation + (29.92 − QNH) × 1000 helps see this: lower QNH (the setting) raises the PA by the corresponding amount. A 0.30 inHg change would give about 300 ft, but a 0.15 inHg change yields about 150 ft.