attila20

Radio/Baro Altitude Mins /STD Baro

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Hallo from a beginner

concerning about this themes I read the Manuals and the Forum, but I can't understand some Details:
Please help me with not too technical Terms.

1. I read, that the Radio/Baro Minimums are required by the Airport
Default Radio=50, Baro is 200)
Tutorial 1 suggests to turn tha value to 100.
In all other extern flight-examples nothing is mentioned regarding this item.
QUESTION: What are the consequences, if the value is too high or low ?
Is the altitude-calculating below this Minimum wrong ?
I read "Radio" is used for Category II and III approaches (A/P and ILS).
And what is "Baro" good for ?

2. The second question refers to the Switch from local Baro to STD and retour.
(HPA in Europe, IN in USA   1013/29.92)
I think over Transition Level the calculation of altitude is the same for every Region all over the world (STD).
But beyond this Level the calculation depends on the Region where you are.
But In no examples (e.g. a book from Tim Rommen) it is recommended to Change this values.
Why ?
Could it be, that These values under Transition Level are the same all over the world ?
Also if you press the "B"-button, nothing happens.
Or is this theme ignored by the Simulation ?

Thank you for every Statement.

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The answer to your first question is on the approach chart.  All instrument approaches have minimums, and there are various minimums but that is a different question.  The standard MDA or DH for a CAT I ILS is 200 ft AGL but it varies, you cannot use a standard value. You must use values from the chart.  ILS CATII & III usually provided minimums as a radar altimeter reading, RA, and again there is no standard.  In fact the RA value may vary from the height above landing threshold if there is sloping terrain under the approach.  Again, use values from the chart.  The basic bottom line rule is that you must go around at the minimums unless you have the runway environment in sight (unless you are authorized for CAT III zero-zero approach).  The runway environment is a FAA term, I'm not sure about other authorities but rules vary.  The runway environment can mean that you can land if at minimums you see the approach lights but not yet is the runway visible, this is exactly what you'll see when at 200 ft AGL and 1/4 mile visibility.

Every nation or authority as in Europe has it's own Transition Altitude, there is no standard.  The STD setting is an option in your PMDG Aircraft Options and is default 18000 (N Amer). The difference between TA and TL is a different quesiton, but Transition Level is often set by ATC depending on barometric pressure.  Again , use the charts for this information.  You switch from local to STD climbing at TA, switch from STD to local descending at TL. The TL value is entered on the descent forecast page in the CDU, the TA is set on the VNAV climb page.

The B key command shortcut only sets local baro.  I have the toggle between local and STD assigned to Ctrl+B using the PMDG Options Keycommand menu (EFIS).

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Hi,

To add to Dan's comprehensive answer:

3 hours ago, attila20 said:

QUESTION: What are the consequences, if the value is too high or low ?
Is the altitude-calculating below this Minimum wrong ?

You have two types of altimeters on an airliner:

_ baro altimeter which basically measures the pressure and compares it to the value you enter using the altimeter to give you an altitude.

_ radio altimeter which measure the heigh above the ground with a radar (usually from 2500ft and below) and is not affected by the altimeter setting.

None of them are affected by the value you enter as baro (DA=Decision Altitude) / radio (DH=Decision Height). These values are for pilot reference only.

The consequences are:

_ If you set the DA/DH too high, then it is conservative, you may go-around earlier than required by the charts. It is safer because your margin is higher but commercially speaking it is not really good because you may create some additional burden at the airport for unjustified go-around and delay at arrival for your passengers.

_ If you set it lower than the chart= Danger! The DA/DH is

calculated to give you enough margin during the go-around to fly over obstacles on the missed approach trajectory. Go around below that value and you may end up in the terrain... in the worst scenario. 

 

3 hours ago, attila20 said:

I think over Transition Level the calculation of altitude is the same for every Region all over the world (STD).
But beyond this Level the calculation depends on the Region where you are.

Basically, above the TL you fly with 1013/29.92 altimeter setting, and below the TA you fly with QNH altimeter settings given by the ATIS/ATC.

You are not allowed to fly in between these altitudes (only climb up or down through the transition layer).

So when at latest you pass through the TA climbing up you will set your altimeters to the standard pressure setting 1013hpa/29.92in (modern airliners have the STD setting for that) and when at latest you descent through the TL you will set your altimeters to the local QNH (you may have to set it earlier but it is another story).

I'm not sure of what you mean by:

3 hours ago, attila20 said:

But In no examples (e.g. a book from Tim Rommen) it is recommended to Change this values.

I cannot remember any situation where you would be allowed to fly with the standard pressure setting below the TA (except of course if the local QNH is the same as the standard pressure).

It is extremely important to set the local QNH because the difference may be up to a few hundreds feet!

 

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Both excellent answers above this one.

Because it's such a comprehensive topic and you indicated you are just starting to learn this stuff, 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!

 

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4 hours ago, attila20 said:

Thank you for every Statement.

A little trivia from back in the mid '70s.  When landing we would set one altimeter to QNH (pilot flying) and one to QFE (pilot monitoring).  

Don't read too much into this it's just trivia. :smile:

blaustern 

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Thank you all for your competent explanations.
@Budbud:
My question was, if I have to Change the value 1013 hPA
to a value depending on the Airport.
and I think now, the answer is "Yes".
The value is to be read in the Charts.

But in all of my flight-trainings there was no hint to do this.
You only can read:
After descend under Trans.Level Change to local pressure
in pressing the "STD" button.
And on the Screen you see 1013 again.
But in real life I think you should Change the value depending on the charts.

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27 minutes ago, attila20 said:

The value is to be read in the Charts.

The TA and sometimes the TL are indicated on the charts but the local QNH (altimeter setting you set instead of the standard 1013) is given by the ATIS and/or ATC and is not a constant value for a specific place but is the corrected atmospheric pressure of the moment and the place.

So it chages from one place to another and changes also with the weather conditions.

For info, the local QNH of an airport is the atmospheric pressure you would read on a barometer at this airport if it was at the level of the main sea level. The value that you can read on barometer at the altitude of the airport is called the QFE. Since the atmospheric pressure decreases with altitude, the higher the airport the higher the difference. So the atmospheric pressure read at the airport is corrected for the altitude of the airport to give you the QNH. (For info, all the altitudes indicated on the charts are referenced the main sea level, hence the need to have the atmospheric pressure based on the same reference to set your altimeters to indicate the same reference based altitude.)

If you follow the tutorial, the local QNH will be 1013 because it is said to fly without weather engine with default conditions. Also your flight trainings may be with default sim weather conditions with the atmospheric pressure set everywhere to the standard.

Also, if you don't use ATIS or ATC, you can use the B key to set the local QNH automatically as a default function of the sim.

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On 13.2.2018 at 5:04 PM, attila20 said:

Also if you press the "B"-button, nothing happens

Because FSX and P3D use the US system with a standard transition altitude of 18000ft all around the world... I believe you can change this somewhere but this change would be global again. 

To add some confusion :D... when you use millibars the phraseology is „QNH“ while flying in the US using inches HG it is „altimeter“... nevermind...

And I believe PMDG have made the function to pre-set the QNH/altimeter with the first use of „B“, the second time sets the value. Not sure on the 737 but I think it works like this on the later addons...

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