How do you set the altimeter for the local field before takeoff?

• A. Set the local altimeter setting (QNH) on the altimeter's Kollsman window as provided by ATC or METAR.
• B. Set the airspeed indicator to standard.
• C. Set the altimeter to sea level.
• D. Leave it as is.

Answer: (A)

Setting the local altimeter pressure in the Kollsman window (QNH) to the value from ATC or the METAR is the way to make your altitude read correctly for that field. This calibrates the altimeter to the actual surface pressure at the location, so the altitude you see reflects your true height above mean sea level. On the ground, with the correct QNH, the altimeter should read roughly the field elevation, giving you a reliable reference for takeoff and climb.

If you set the altimeter to sea level, the instrument would indicate altitude relative to a zero pressure reference, not the local conditions, causing your readings to be off by the field’s elevation. Leaving the setting unchanged or using an outdated/incorrect value also risks inaccurate altitude readings. Changing the airspeed indicator to standard or any setting for the altimeter won’t affect the altimeter reading, since that instrument’s purpose is pressure-based altitude, not airspeed.