MDA vs DH /DA

[Farid]

why the pilots usually use MDA instead DA even for ILS approaches?

any replay would be appreciated

[Aynayda Pizaqvick]

None of the pilots I know do. DA/DH (decision altitude/height) is used for Precision Approaches i.e. those with electronic glide path information such as an ILS. Its the height that you decide whether you have the required visual references and if not, carry out your go-around using minimum height loss technique for your aircraft i.e. you will likely fly below your DA/DH.
MDA/MDH (minimum decent altitude/height) are used on non-precision approaches and is the absolute minimum that you can descend to and will have a missed approach point.
Whether you use an altitude or height depends on the airport you are flying at but most these days use QNH so you should be using a DA or MDA. UK Military airfields still use QFE so you fly to a DH/MDH and the altimeter should of course read somewhere close to zero on touchdown.

[charlie83]

Not in the UK airline I fly for...

MDA is used for Cat1 ILS as it's baro referenced.

CAT2/3 is auto land (in my outfit) and Rad Alt based, hence DA is used.

[Capn Bloggs]

MDA is used for Cat1 ILS as it's baro referenced.

I don't think so.

[streetcar driver]

Farid,

I think Aynayda Pizaqvick gave a good explanation.

Nevertheless, on most Airbus aircraft, you can either select a MDA (based on altitude - air data) or a DH (based on height - radio altimeter). Although the terms are not used in accordance with standard JAA phraseology, it works as expected. Select a MDA and your indicated minimum is based on your air data computer, select a DH and your indicated minimum is based on your radio altimeter.

Hope that explanation helps

streetcar driver

[Tmbstory]

Farid:

Would this help you, It is from PAN OPS ICAO.

TMB

[fireflybob]

Other threads have been running on this topic, here is one:-

MDA and all that jazz

[Right Way Up]

As mentioned before this sounds like an Airbus issue where the minima inputted on the FMGC perf page can either be Baro referenced by inputting in the MDA box or radalt referenced by inputting in the DA box. This gives the confliction of suggesting an ILS has an MDA when all it is allowing minima calls based on baro alt. I believe an update to the software will shortly change the items from MDA to BARO and the DA to RADIO.

[charlie83]

^^^^Correct.


Appologies for being vague in the earlier post.

[FlightPathOBN]

This thread also addresses much of the same issues...

http://www.pprune.org/tech-log/44188...cision-da.html

[compressor stall]

An understandable question - WRT to the Airbus FMGC and putting the CAT 1 minima into the MDA box, I remember scratching my head and asking the same question during my endorsement.

[n77]

Originally Posted by streetcar driver

Nevertheless, on most Airbus aircraft, you can either select a MDA (based on altitude - air data) or a DH (based on height - radio altimeter). Although the terms are not used in accordance with standard JAA phraseology, it works as expected.

streetcar driver

In the latest bus fmgc software you have baro/radio instead od mda/dh