Q400 DH vs. MDA

[srmj71 0]

 I'm about six months into my sim career, so please give this noob a little altitude... something I haven't had much luck resolving with research, is DH/MDA, and how to properly use this. My question is do you use both of these, or just one? On approach plates, you get two minimum altitudes take KMDT ILS LOC RWY 31, you have both 558/50 and 250/(300-1).

Can someone give me a quick rundown on the intended usage? I'd really appreciate the help.

[BrianW 124]

Use MDA (barometric) for a CAT I ILS, or any non-precision approach.  Use DH (radar altitude) for CAT II approaches. You’ll see RA listed in the minimums as a reminder to use DH, KMDT ILS 13 CAT II & III for example.

[mikealpha 266]

 generally a good explanation regarding the subject : How to get the correct approach minimum :

 

 

[srmj71 0]

Ok, a little follow up, the landing category you are in is determined by your Vref, which in turn is determined in part by the aircraft's weight. Roughly speaking, unless you are in an aircraft with some pretty wildly varying performance characteristics, you will always be in the same landing category. Am I on the right path?

 

Thank you for your help with this.

[mikealpha 266]

1 hour ago, srmj71 said:

Roughly speaking, unless you are in an aircraft with some pretty wildly varying performance characteristics, you will always be in the same landing category. Am I on the right path ?

Theoretically yes, but the speed border between two categories can be just near the middle of your Vref range. E.g. the border between Category B and C is a strict 121 kt. If you look at the Dash-8 speed cards, you`ll find that border depending on weight for every Flap setting. 

Mike

[DaveCT2003 1,820]

Interestingly enough, I just posted this to another user!  Must be something in the water!  LOL!!!

I've provided a link to a PDF that I created from an AVSIM discussion on about Decision Height vs. Decision Altitude a few years ago and some additional information I had added. I gave this to new pilots who would come fly with us.

I think/hope it will be helpful to you.

Decision Height vs. Decision Altitude PDF Download

 

Best wishes!

 

[srmj71 0]

I really appreciate the time you guys took to help me out with this. I'm so badly hooked on the sim, that when I can't figure something out, it eats at me... something fierce. Take care,

Steve 

[DaveCT2003 1,820]

2 hours ago, srmj71 said:

when I can't figure something out, it eats at me... something fierce.

Proof we have the makings of a great and knowledgeable flight simmer right here in front of us!  Nice.  Very nice indeed!