Questions about approaches

[Mark Meeker]

I am new to this site, and like it very much. I am preparing to take my Practical FAA examination for an Aircraft Dispatchers Certificate. I have passed the ATP already.
I have a question, that has always confused me about approaches. Can someone explain in plain language the differance between a Decision Height (DH) and Decision Altitude (DH). From what I understand, DH is height AGL and DA is MSL or am I confusing these, or off clue completely. Thanks
Mark

[CMN]

Height is always with reference to the ground (AGL)
Altitude is always with reference to MSL.

So a category I ILS to a runway at 150 feet above mean sea level can have a DH of 200 feet and a DA of 350 feet.

[mad_jock]

Its dates back to mainly a UK thing and these days purely a UK Military SOP

A decsion height is one which you would use when you fly the approach using QFE on your Alt which is the airfield pressure to give 0 ft on the threshold.

A decsion Altitude is used on an approach which is flown with the QNH set on the alt.

[Mark Meeker]

Thanks, I appreciate it

[Wirbelsturm]

Whilst only for the Military in the UK, some foreign fields still use QFE for the approach (Russia!) thus requiring the conversion of QNH to QFE in flight for the calculation of minima often leading to EGPWS pull up warnings when the correction is applied in the wrong direction!!!!

Moscow anyone!