# Is this an accurate method to showing how the correct Decision Altitude/Height for an approach has been determined?

Here's my method of summarising how the decision altitude/height for an approach was determined:

DH/A =
The highest base altitude/height from the list below +
Altimeter Pressure error +
Altimeter Temperature Error +


Base altitude/height:

1. OCA/H
2. System Minima e.g. ILS 200ft, VOR/DME 250
3. OCA/H per aircraft category
4. (Otherwise) Published approach DA/H
5. Minimum A/H to which the approach aid can be used
6. Minimum A/H in the Aircraft Flight Manual

Instrument Rated pilots will need an understanding of how the DA was determined, they may be examined on it in theory tests and skills proficiency tests - though whilst actually flying the approach they will use the plate DA.

Is this summary correct, or how would you alter it?

• The correct method is to hire a mechanic to fix all that error in your altimeter. Then set it to the local airport pressure setting. I don't know where you are flying but around here we don't have unverified approach navaids or published terminal procedures without a listed DA/MDA. Without a published procedure it is either a standard VFR approach or your company has developed its own approach which will be verified and have a DA or MDA. Why or how would an aircraft manual have procedure altitudes? – Max Power Sep 2 '20 at 9:53
• Generic system minima is used by the engineer designing an approach, it really has no common use for pilots, all systems will have a published approach with listed minima. IMC flight below MOCA requires a published approach. A visual approach has no DA/MDA. – Max Power Sep 2 '20 at 10:09
• @MichaelHall flying – ob318 Sep 3 '20 at 9:16
• @MaxPower Instrument rated pilots need to understand how the DA on a plate is determined (not just unknowingly accept it without comprehending how it is determined). This formula was my attempt to remember. – ob318 Sep 3 '20 at 9:17
• @ob318, while I agree it is useful to understand why certain things are the way they are, when you are flying an approach to mins you don’t need to “determine” the DA, it has already been determined, and published. If you are designing an approach that’s a different story. In that case the published is irrelevant because you haven’t determined what it should be yet. Right? You are mixing things in a confusing way and I am going to vote to close this until you can clarify the question. – Michael Hall Sep 3 '20 at 15:53