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Michael Moe

RVR and DH

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Another question i cant decode via wiki.

 

If the ATC for a given approach requires CATIIIB and the ILS Chart say CATIIIB avaible. What is the DH? Maybe the METAR says 100m RVR. How do i count those 100m and what has first priority during the FA? DH or RVR.

 

How do i know what to set the Radio altimeter to?

 

Thanks

 

Michael

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CATIII approaches do not have decision heights. As far as I know they are autolands and CATIIIC do not have minimums associated with them.

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RVR and DH are two different things. For simulation purposes, if published RVR conditions exist, you can fly with published DH minimums.

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Cat III approaches do not have decision heights--they are intended for a fully automatic landing where the pilot may not even see the runway environment before touchdown.  Cat IIIA and IIIB will have visibility minimums, and Cat IIIC is legal down to zero-zero, so no published mins there.  Which one you can fly will depend on the aircraft (certification and operating equipment vs MEL requirements) and the crew's certification level (driven by training and experience level).

 

Regards

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Well you are all wrong. Only fail operationel does not have DH and RVR on a autoland CATIII A or B. Ralph has a very good video training on that. Thats called alertheight btw. But how do i measure RVR from the cockpit?

And what about the DH determination? From a fail passive point of view. Typically this would be in between 0-50 feet but who is calling 37 for instance?

 

Michael

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Well you are all wrong.

My My, I'm willing to bet you'll get a LOT more helpful responses in the future.

 

In any case, you happen to be wrong yourself. Alert Height and Decision Height are not the same thing.

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What do you mean "how do you measure RVR from the cockpit"? 

 

RVR is runway visual range and it is given in the METAR. You don't measure this with a "broom stick" from the cockpit.

 

ILS Cat 3b -fail operational: DH 0ft 

ILS Cat 3b - fail passive:  DH 50ft 

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Well you are all wrong. Only fail operationel does not have DH and RVR on a autoland CATIII A or B. Ralph has a very good video training on that. Thats called alertheight btw. But how do i measure RVR from the cockpit?

And what about the DH determination? From a fail passive point of view. Typically this would be in between 0-50 feet but who is calling 37 for instance?

 

Michael

 

Well, no we're not all wrong.  There's a difference between minima imposed by the procedure itself, and restrictions imposed by company policy or the AOM.  Fail passive ops restrictions, in particular, are limitations imposed by policy or AOM due to partially inoperative equipment, not by the IAP itself.  Many operators also have more restrictive standing operational limits of their own, some for all crews, some for certain aircraft, and some based on the experience level of the crew.

 

DH and AH are not even close to the same thing, either.  The AH is used to make a final evaluation of system status for a decision on continuing the Cat III approach and autoland.  The DH is the latest point where a land/no-land decision is made based on visual contact with the runway.

 

RVR is measured by light transmissometer readings made by instruments located near the approach end of the landing runway, and is reported by ATIS and/or ATC.

 

Regards

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Guys sorry if the words was wrong choosen. I did not try to be a beast :-) i know DH and AH is different. I was just under the impression that the pilot has to make visual reference on fail passive and since the DH is 0-50 feet i am just lost. I thought you would or should count the lights or sonething. And secondly. Why would i choose a DH37 aand not just 0 or 50?

 

No hard feelings my fellow sinmers:-)

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Concerning fail-passive systems the decision height is 50 ft. 

 

FAA:

(AC 120-28D)

"Category IIIb operations based on fail passive landing systems meeting provisions of Appendix 3 of this

AC, or equivalent, must use a decision height not less than 50 ft. HAT." 

 

EU:

(CS-AWO 304)

"For decision heights below 15 m (50 ft), 

a fail-operational landing system (automatic or 
hybrid) must be provided which, when 
appropriate, includes provision for control of the 
aeroplane along the runway during the ground 
roll down to a safe speed for taxying. "

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Guys sorry if the words was wrong choosen. I did not try to be a beast :-)

 

Try a bit harder, it will do you well.

 

 

 


I was just under the impression that the pilot has to make visual reference on fail passive and since the DH is 0-50 feet i am just lost. I thought you would or should count the lights or sonething.

 

Yes he has. There are guidelines of what you have to see. For example a regulatory document (manual, FAR etc.) could say that you need to see three bars of the approach light system.

 

 

 


And secondly. Why would i choose a DH37 aand not just 0 or 50?

 

Na-ah. YOU don't choose nothing. You do what you are told - these values are chosen by someone for reasons. If they come to a value of 37, it has probably something to do with runway shape/slope, obstacles etc.

 

Also noted fail-passive is not (generally speaking) CAT IIIb level, rather CAT IIIa level (barring exceptions, such as noted in Daniels post, outlined in Appendix 3 of the relevant document)

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Thanks but if i am not choosing the DH will it be reported by ATC then?

 

Those lights i might count would be a control of the equipment for RVR i guess. If the RVR changes midway a Weather update?

 

Thanks Michael

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DH is not reported by ATC, it is published on the chart for the approach in question...

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Also, any significant RVR change during the approach is reported by ATC (in the realworld) until the aircraft has landed.

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For what it's worth, ATC-wise, RVR will be reported on frequency if it changes.  This is the same as when controllers say "attention all aircraft on frequency, information Echo now current: [changes in weather from info Delta]."

 

This may also be optionally added by the controller when clearing aircraft for the approach or landing.  It's not standard (though the 7110.65 3-10-1 lists it as "any supplementary information" as part of standard landing information), but some controllers do it just to ensure pilots have the most up-to-date information.  This is the same as when controllers say "wind 020 at 9, Runway 1R, cleared to land."  They would just add the RVR between the wind and the landing clearance.

 

Additionally, the controller does have access to all of the charts (to include company-specific procedures) at their console.  Depending on the facility, a controller will have some sort of tool to pull up all kinds of info.  Potomac Approach (PCT) has theirs up above the radar console, and it is able to display basic aircraft information, all charts for relevant airports, and even menus for local restaurants (PCT is in the middle of nowhere so they generally have to order in, and order early if it's going to get there by the time they take a break - even local restaurants that don't do delivery have worked out an agreement with them to help them out).

 

So, just in case you drop your coffee on your chart and ruin it, you could ask them ahead of time to verify the info and they could do it.

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DH is not reported by ATC, it is published on the chart for the approach in question...

Could not understand that either. That why i in the originale post mention that my ils charts always just state CATIIIB avaible or CATIIIA.

 

Thanks

 

Michael

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That why i in the originale post mention that my ils charts always just state CATIIIB avaible or CATIIIA.

 

...and at the bottom, there will be the requirements.  What it seems that you're not understanding is that CAT III approaches are approaches that were created for and are certified for zero vertical visibility.  As such, there's no DH (for CAT II, it's listed as RA here: http://155.178.201.160/d-tpp/1405/05100I1LC2_3.PDF; for CAT IIIa and IIIb, it only lists RVR - 700 and 600 feet, respectively).

 

In order to understand how to read charts, I suggest having a look at this:

http://www.vatusa.net/training/tiki-index.php?page=reading_instrument_approach_plates

 

If it says "CAT IIIb available" without any mention of RVR, chances are, it's on another chart and you're looking at the wrong one.

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what has first priority during the FA? DH or RVR.

Both have "priority" when you have both.

 

Generally speaking, Three requirements need to be fulfilled to descend below DH / DA / MDA

 

• Flight Visibility (e.g. reported as RVR not below mins)

• Visual Reference to the Runway* (see below links as too long to list here)

• Continuously in a position to make a normal descent to landing (135/121 have an extra requirement)

 

§91.175 covers the specifics, particularly what visual references are acceptable.

 

§91.189 covers the specifics applicable to Cat II & Cat III approaches.

 

There's also mention in 91.189 regarding "operating an aircraft using a Category III approach without decision height" which goes right back to Col. Scott has previously covered.

 

 

That why i in the originale post mention that my ils charts always just state CATIIIB avaible or CATIIIA.

 

I am a bit curious which charts you are referring to.

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I am a bit curious which charts you are referring to.

 

Yeah, same.  It really shouldn't be this hard if it's the charts I'm used to.

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Guy should probably go watch Ralphs video as well.

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Yeah, same.  It really shouldn't be this hard if it's the charts I'm used to.

 

 

Hmm thanks . I use Navigraph charts and i dont see RVR under CATIII

 

ils22_L.jpg

Both have "priority" when you have both.

 

Generally speaking, Three requirements need to be fulfilled to descend below DH / DA / MDA

 

• Flight Visibility (e.g. reported as RVR not below mins)

 

 

 

 

So i am wrong when i say its up to captain to deside whether the RVR as stated by ATC is as it should be and i can continue my approach if at my DH i believe so ?

 

Some peoble her say i am not in charge of RVR measurement but if i am afterall (responsiblity) i need tor learn to measure the lights or whatever the airport is using from the pilot side.

 

Sorry for my stupid Questions . I do love your answers though. Much apreciated fellow simmers :-)

 

Michael

Guy should probably go watch Ralphs video as well.

 

 

I did twice :-) Can you explain me the DH he maid in the GOAround video and why? He was performing an Autoland in the Go/Around video

 

Thanks

Michael

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So i am wrong when i say its up to captain to deside whether the RVR as stated by ATC is as it should be and i can continue my approach if at my DH i believe so ?

 

For this CAT III Part 121 stuff, I have no clue.  We need an adult to step in (RSR... Col. Scott...).  I do believe there is some requirement that reported visibility (e.g. RVR) has to be at or above the required visibility minimum on the approach chart in use to legally fly the approach.

 

Under U.S. Part 91 (basically "non-commercial" i.e. not charter and not airline) if the reported visibility is less than what is required on the approach chart, you can attempt the approach (iirc!) but if you land and there is a reported RVR of less than 2400' (and this referring to a CAT I ILS approach*) one is going to have a very difficult time demonstrating to the FAA the flight visibility was 1/2sm or better.  (Turn on that GoPro before the middle marker and have a good attorney  :lol:  ).  

 

 

Also, with respect to your chart, there should be one for the CAT III approach @ EKCH.  I found a Jeppesen that has the CAT II with minima the same as the Navigraph (although it did list a DA / DH also).  As an example, here is a link to a U.S. Government chart (pdf) for the Indianapolis (KIND) ILS RWY 5R (CAT II & III).

 

Google CAT IIIB EKCH and you should be able to find at least a Jeppesen pdf that includes the CAT II approach (I could not find the CAT III).  

 

Your questions are not stupid... some of this stuff can be quite complicated and it definitely going to vary on the type of operation.

 

-------------

*Not referring to the CAT I ILS to 1800'RVR

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Hmm thanks . I use Navigraph charts and i dont see RVR under CATIII

 

While my family is part Danish, they still confuse me from time to time.  There should be RVR listed in that block that says "available."  My guess is that it's on another chart that has "CAT III" as part of the title.

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