Hi,

 

the title says it all: When would I use minima as altimeter, and when as height? The Approach Plates indicate barometric minima in bold letters and radio minima in brackets behind and I always ask myself, "what do I use now", and usually I end up using barometric minima. How is it done correctly?

 

Thank you very much!

Precision Approach = Decision Height = Radio

Non-Precision Approach = Minimum Descent Altitude = Baro

 

The brackets figure on Baro minimums is just your equivalent height AGL.

MDA is "don't go below unless visual"

DH is lowest height to commence go round if visibility does not satisfy minimums

Generally you would want to use baro unless noted on the chart.  Usually CAT II and III approaches will use RA because you’ll already be over the runway environment by the time you reach the minimums.  

 

Using RA on a CAT I has the potential to have you descend lower than what’s safe if the airport sits on a plateau or has terrain that sits much lower on approach than the airport.

Using RA on a CAT I has the potential to have you descend lower than what’s safe if the airport sits on a plateau or has terrain that sits much lower on approach than the airport.

 

Can you give such an example? A Cat 1 ILS is a precision approach and uses RA

Here are two approaches for my home airport.

 

CAT I BARO

https://skyvector.com/files/tpp/1612/pdf/00142IZLDZ16R.PDF

 

CAT II RA

https://skyvector.com/files/tpp/1612/pdf/00142IZ16RSAC2.PDF

 

 

Both are pretty popular approaches for 777's  :wink:

Can you give such an example? A Cat 1 ILS is a precision approach and uses RA

 

It doesn't, actually.

 

You only use RA where the approach plate states "RA."

 

While this approach provides an "RA-like metric" in the "200," it's simply letting you know that the min of 512 happens to be 200 AGL:

http://155.178.201.160/d-tpp/1612/05100IL1R.PDF

 

This approach, on the other hand, specifies RA in the metric, so you use radio alt. Note that in this case, DA is provided to let you know that the DH of 94 will put you at 412 MSL. Note the variation of 6' between the DA, and reference DH vs TDZE. This iswhy you do not substitute them for each other. While in this case the variance is only 6', imagine the variance between the runway data plane (based off of the TDZE) and the reading somewhere like KSEZ, which is on a plateau. If it had an ILS, and you flew it to RA mins...

"Tonight! At 11..."

 

http://155.178.201.160/d-tpp/1612/05100I1RC2_3.PDF

(Note the "RA" clearly stated.)

I always thought that the number in brackets would be RA! But now I know it's AGL.

 

So it's either RA, and then it is explicitly stated, and if not, it is Baro. Thank you very much for your insights.

 

 

So it's either RA, and then it is explicitly stated, and if not, it is Baro. Thank you very much for your insights.

 

Welcome!

Very informative post.

Thanks !