I am a longtime subscriber to Aviation Safety and recommend your publication to my clients as the best aviation magazine out there. However, in your August issue, the article on IFR GPS had what I believe were a few errors in an otherwise informative article. The author describes DH (decision height) as a height above sea level and DA (decision altitude) as “above runway.” This explanation is likely to confuse people trying to understand this concept because it is the opposite of the correct definition. 288
Decisions, Decisions
I am a longtime subscriber to Aviation Safety and recommend your publication to my clients as the best aviation magazine out there. However, in your August issue, the article on IFR GPS had what I believe were a few errors in an otherwise informative article. The author describes DH (decision height) as a height above sea level and DA (decision altitude) as "above runway." This explanation is likely to confuse people trying to understand this concept because it is the opposite of the correct definition. Instead, DH is an agl altitude and DA based on msl. The FAA describes it similarly, using a few more words, as follows: "Decision Altitude/Height (DA/H): A specified altitude or height (A/H) in the precision approach at which a missed approach must be initiated if the required visual reference to continue the approach has not been established. Note 1: Decision altitude (DA) is referenced to mean sea level (MSL) and decision height (DH) is referenced to the threshold elevation." The other statement with the potential to cause confusion was, "a WAAS box will automatically suspend when you pass the missed approach point," which might lead one to think that a non-WAAS GPS will not. In fact both non-WAAS and WAAS GPS navigators suspend when passing the MAP.
Key Takeaways:
- The magazine issued corrections regarding IFR GPS information, clarifying that Decision Height (DH) is an AGL altitude while Decision Altitude (DA) is an MSL altitude for precision approaches.
- It was also clarified that both WAAS and non-WAAS GPS navigators automatically suspend upon passing the missed approach point (MAP).
- A reader critiqued "zero-zero departures," emphasizing that safety primarily involves preventing difficult situations rather than relying on training and equipment to resolve self-created predicaments.
- The same reader also expressed preferences for traditional traffic pattern entries over straight-in approaches.
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