Welcome to another S.O.A.R post, today we will be explaining MDAs, DHs, their differences and practicalities. 

Flying on instruments demands precision and discipline. When weather prevents a clear view of the runway, pilots rely on published approach procedures to guide them safely. Among the most important terms in these procedures are Minimum Descent Altitude (MDA), Decision Height (DH), and Minimums. Although closely related, each of these terms carries a specific meaning that every instrument pilot must master.

Minimum Descent Altitude (MDA)

MDA applies to non-precision approaches, such as VOR, NDB, or Localizer approaches without vertical guidance.

It is the lowest altitude a pilot can descend to on final approach without visual reference to the runway environment. If the required runway cues are seen before reaching the missed approach point, the descent may continue to landing.

If not, the aircraft must stay at or above MDA until the missed approach point, and then the missed approach procedure is flown. Unlike with DH, the pilot may level off and fly at MDA while searching for visual reference.

Decision Height (DH)

DH (sometimes called Decision Altitude, DA) is used in precision approaches such as ILS, or approaches with vertical guidance like RNAV LPV.

It is the exact point on the glide path where the pilot must decide: continue the descent and land, or execute a missed approach.

At DH there is no level-off option. If the runway environment is not in sight at that precise point, the only correct action is to go around immediately.

Reading Minimums on Charts

On an approach plate, the Minimums section usually appears near the bottom. Each line shows:

• The type of approach (e.g., ILS CAT I, LOC, LNAV, LPV).
  
• The minimum altitude (MDA or DA/DH).
  
• The required visibility in statute miles or meters.
  
• Sometimes the Height Above Touchdown (HAT) for clarity.
  

For example, an ILS might list DA(H) 200 ft / ½ SM visibility, while the same runway using Localizer only might require MDA(H) 680 ft / 1 SM visibility.

Approach Categories

The published Minimums also depend on the aircraft’s approach speed. Faster aircraft need larger margins for maneuvering, which translates into higher Minimums.

• Category A: less than 91 knots
  
• Category B: 91–120 knots
  
• Category C: 121–140 knots
  
• Category D: 141–165 knots
  
• Category E: more than 165 knots (rare, usually military or large jets)
  

Charts display Minimums in rows according to these categories. Each pilot must select the correct row based on their aircraft’s approach speed. For example, a Category B aircraft might have an DH of 407 feet, while a Category D aircraft on the same procedure could require a DH of 425 feet.

This will be all for today’s S.O.A.R blog. Thanks for reading and see you next time 🙂