FAA Aviation Mechanic Airframe (AMA)Airframe Electrical and InstrumentsMedium
A pilot preparing for a flight above 18,000 feet MSL sets the Kollsman window on the altimeter to 29.92 inches of mercury. What does this setting represent?
- AThe standard sea-level pressure reference used to display pressure altitude
- BThe current local station pressure at the departure airport
- CThe true altitude above mean sea level, corrected for temperature
- DA correction factor for density altitude at the current temperature
Show answer & explanationAnswer & explanation
Correct answer: A. The standard sea-level pressure reference used to display pressure altitude
29.92 in Hg is the standard atmospheric pressure at sea level. Setting the Kollsman window to this value causes the altimeter to display pressure altitude, which is required above the transition altitude (18,000 feet MSL in the U.S.) so all aircraft reference a common pressure datum.
Why the other options are wrong
- B. Local station pressure is used below 18,000 feet, set from ATIS/ATC, not 29.92 fixed.
- C. True altitude requires temperature correction beyond the barometric setting.
- D. Density altitude requires a separate calculation involving temperature, not a Kollsman setting.
Kollsman Window / Pressure Altitude
The altimeter setting window; setting it to 29.92 in Hg standard pressure causes the altimeter to indicate pressure altitude, used above 18,000 ft MSL.
- 29.92 in Hg is standard sea-level pressure
- Used above 18,000 ft MSL for common altitude reference
- Local altimeter setting is used below 18,000 ft MSL
Memory trick: 29.92 = the standard 'reset button' above 18,000 feet