Decision Altitude is expressed in which datum?

Decision Altitude is expressed in which datum?

• A. AGL
• B. MSL
• C. No altitude unit
• D. Both AGL and MSL

Answer: (B)

Decision altitude is tied to mean sea level. This reference keeps the published minima consistent across airports with different elevations and terrain, so a pilot can interpret the same DA value anywhere. If you used height above ground (AGL), the same DA would correspond to very different altitudes at different airports, causing confusion. The altimeter is set to the local pressure (QNH) so the reading reflects altitude above sea level, which is why the standard datum for DA is MSL. Therefore, it is not expressed in AGL, nor is it given with no unit, and it is not a mix of both.

Decision altitude is tied to mean sea level. This reference keeps the published minima consistent across airports with different elevations and terrain, so a pilot can interpret the same DA value anywhere. If you used height above ground (AGL), the same DA would correspond to very different altitudes at different airports, causing confusion. The altimeter is set to the local pressure (QNH) so the reading reflects altitude above sea level, which is why the standard datum for DA is MSL. Therefore, it is not expressed in AGL, nor is it given with no unit, and it is not a mix of both.