ADI DH REF

[dreamboxlouisville]

Ok dumb question maybe but where/what chart do I find the ADI references to set the height.

[Broeselmappe]

Any Instrument appproach charts. Unually a table at the bottom.

[Fabio Pittol]

Source: https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dtpp/search/results/?cycle=1606&ident=JFK

Look at the line S-ILS 4L.

• 223/40 means: Decision Altitude (Baro) =  223ft / RVR * 100 = 40ft
• 210 means: Decision Height (Radio) = 210ft
• (310-3/4) means: Military-only

This is for the FAA-style charts, that are available through their website.

A lot of other sources only list as: DA(H) - 223 (200), which would mean Altitude (Baro) and Height (Radio).

As the other guys said, it's always at the bottom of the approach charts.

[Litjan]

All correct, but not relevant to the question - this is the barometric decision height used in a CAT I approaches and will never be set on the ADI DH window. That window is exclusively for radar altitude decision heights, and those are only used for CAT II and CAT IIIa approaches. For the 737 the DH is around 100 feet for CATII (you can find the value on the charts) and always 50´ for CAT IIIa approaches.

So you need to dial that value to -20 for most approaches (that way it blanks and doesn´t call minimum), UNLESS you do a low-visibility CAT II or CAT IIIa approach.

Jan

 

[dreamboxlouisville]

Thanks for the info guys. Really helps out !!

[jailer]

On 6/3/2016 at 7:19 PM, Litjan said:

All correct, but not relevant to the question - this is the barometric decision height used in a CAT I approaches and will never be set on the ADI DH window. That window is exclusively for radar altitude decision heights, and those are only used for CAT II and CAT IIIa approaches. For the 737 the DH is around 100 feet for CATII (you can find the value on the charts) and always 50´ for CAT IIIa approaches.

So you need to dial that value to -20 for most approaches (that way it blanks and doesn´t call minimum), UNLESS you do a low-visibility CAT II or CAT IIIa approach.

Jan

 

I've been watching a lot of 737 cl videos on youtube, and it seems quite a few times I've seen pilots use the RA DH and brief during the approach briefing that it was for (I don't remember exact phrasing) but either situational awareness or advisory purposes only.  Is this a company SOP thing, bad habit, or just quirk to that flight crew?  It seems like it's handy.  Perhaps +50 from the indicated AGL for safety factor?  I just like hearing "minimums" but that's just because I think it's cool. 

[Litjan]

I don´t think there is any rule agains using it for situational awareness - but if you set it to "200" and use it to alert you of the MDA you might bust your limit if there is a valley or gorge in front of the runway. To use the DH for a minimum you need to have the ground charted and measured - thats why the 100 feet for a CAT II is often stated as a slightly different value. The mapping team will take the highest spot within a certain perimeter of where the plane is when it is 100 feet above the runway threshhold. If that is a small mound of say 5 feet, the resultant DH will be 95.

The CAT IIIa is always 50 because you will be over the runway when it sounds - and that is usually flat.

You can set the DH for anything else you like (although I would consider it bad airmanship - don´t use an alert for anything else, it will loose it´s significance in your mind).

Jan

 

[Iain]

Holy thread resurrection Batman!  I'm currently flying a TUI 737 from Humberside to Corfu, flaps 15 takeoff, used the full length but got 35ft over the end easy!

 

Anyway, LGKR chart is a VOR approach, minimums at 2000ft, how would you set this up in the IXEG, or simply can not be done due to only having 3 digits.  Is this the same story in real life for the -300?  Long time since I flew PMDG so can't remember if it has 4 digits.

Cheers

[Litjan]

Hi Ian,

at the risk of repeating myself - you will NOT use the DH for a Non-Precision (VOR, LOC, NDB,...)  or ILS CAT I approach. It is ONLY for CAT II or CAT IIIa approaches. These approaches have a DH of ca. (depending on the elevation around that spot) 100 feet RA and 50 feet (always exactly 50 feet because that is over the runway) RA.

For all other approaches you will use the orange "minimum" bug on the altimeter. Set it to the desired minimum (so for 2000 feet set it at the 12 o clock position) - you have to remember the "thousands"... in example the position of the bug would be at the same position for minima of 690feet, 1690 feet, 2690 feet... remember you are flying a Boeing, come cerebral activity is required and expected .

Cheers, Jan

Edited November 11, 2019 by Litjan

[Iain]

Got it! Thanks for the explanation.

[hawabaz]

Dear I want to ask for a query. It is said that do not set DH on the EADI for non precision approach.  I have observed few pilots who set MDH on the radio Altimeter on the EADI and they are comfortable doing it. Pls explain why it is not recommended?

 

Thanks!  

[Litjan]

It is not recommended (and even against regulations) because the radio altimeter will say "minimums" when it measures 200 feet radio altitude. But since the terrain in front of the runway may be a hill or a valley, this may not really be "200" feet above the threshold - as it is required for a CAT I minimum.

If the terrain in front of the runway is very flat, this will work. But legally it is required to reference a DA (decision altitude) with regard to MSL - not a decision height with regard to radar altitude, like you would on a CAT II or CAT III approach.

Even on a CAT II approach you will often not set your DH to 100 feet - but to 98 feet or to 102 feet or so - to allow for undulating terrain in front of the runway threshold.

[AngelOfAttack]

IRL you'll have PM to call out the DA\MDA on baro-altimeter. However most of us in sim don't have that luxury,  so when flying 733(with 757/767/A310 etc..)I‘ll set RA to DH on chart for automatic callout, and still double check the baro altitude for sure if it's near limit.

Most of the time with real weather you'll see the runway like at least 1000' AFE so it doesn't matter that much...

[Litjan]

@AngelOfAttack That is certainly viable - and I know some airlines also use the DH to provide some sort of terrain awareness. However, you still get the automatic radio altimeter callouts, so if your minimum is 200 feet above the threshold, the automatic "200" callout will double as a (close) reminder.

When approaching in considerably better than minimum weather conditions we used to be just brief "minimum is visual" but that was later reversed as sometimes weather was surprisingly worse than expected and no minimum was set that the crew could refer to as the plane got closer to the runway but could not pick it up visually.