SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/ifr-da-msl

A decision altitude (DA) on an approach chart is measured relative to what?

DA is an MSL altitude.

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  1. Height above the ground (AGL)
  2. Pressure altitude at 29.92
  3. Mean sea level (MSL) ✔

Why: Decision altitude follows the international convention: altitudes are measured from mean sea level and heights are measured above ground level. DA replaced the older term decision height.

Huh, didn't know that: Decision altitude is flown by the barometric altimeter, and a missed approach starts there if the visual references are not in sight.

The dad joke
DA stands for decide already.
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References

Answer: Mean sea level (MSL). Decision altitude follows the international convention: altitudes are measured from mean sea level and heights are measured above ground level. DA replaced the older term decision height.

  1. FAA Aeronautical Information Manual 5-4 Instrument Approach Procedures www.faa.gov/air_traffic/publications/atpubs/aim_html/chap5_section_4.html
    DA conforms to the international convention where altitudes relate to MSL and heights relate to AGL.
    Checked 2026-10-10.

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Test yourself in the game

FlyingUsing only the approach lights as your visual reference, how low may you descend below DA?FlyingThe authorized DA/DH or MDA for an approach is which of the available values?FlyingBelow DA, which condition must you meet to continue to land?

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