DA = above sea level

 

DH = above runway level.

 

Now, I am going to disagree with Ralph a bit, but that might be geographical (I have not dealt with FAA-land).

 

There is no inherent connection of DH and radio altimeter. In fact, it could prove dangerous in some cases.

 

Now, for CAT I approaches, you will typically have a DH of 200. DA therefore is touch down zone elevation + 200ft.

You will want to go barometric on that. Why?

 

Because 200ft ARL is actually quite a bit from the threshold, and the terrain there can be decieving for a radio altimeter.

If the terrain climbs, looking from the runway, you will meet 200RA sooner than 200 ARL. Sometimes even significantly sooner. Sometimes you may find that you might actually be legal, if you flew couple hundred meters further.

If the terrain descends, however... you would find yourself having 200RA alert later than you should. So you might think you are OK but actually bust minimums. That could end bad, if you had an accident or an incident.

 

Going down to CAT II and CAT III, you are getting to the area, where you have reasonable, dependable RA reading, as you are often already over the runway itself. So you would use RADIO mins.

Sometimes, your charted minimums differ a bit. For example. for Stuttgart RW25, there is CAT II minimum of 110ft. But, in the next line in the LIDOs, there is a value, and it states 115RA, so you would set radio minimums at 115. That would mean, that the point where airplane should be at 110ft above touchdown zone is 5ft lower in elevation as actual TDZ. 

Conversely on the other end of the same runway, minima are 100ft, but 90RA is noted.

The runway gains almost 100 feet in elevation between TDZ on either ends, and you can see it goes on for a bit beyond TDZ.

 

FWIW, in CAT I minima, there is 1390 for RW25, which equals 1181ft of TDZ elevation, plus 200ft CAT I minima, plus rounding up to nearest ten feet.

I'd like to eliminate confusion where and if possible.

 

@Fabo is correct. He is speaking from a real world perspective and I was speaking more from a textbook, perfect world, kind of perspective.

 

While a CAT I ILS might have a published 200' AGL DH, instrument pilots will (or should) always know what the MAP (Missed Approach Point) altitude is in MSL. And that's what Peter is saying.

 

I know what he is referring to as I have seen it happen several times. You're on a CAT I (or at least not a CAT II or III) ILS approach and on short final, and the radar altimeter starts to 'slap' around the dial, jumping up to peg at 2500' which is their high limit for some, and then jumping back down to some lower value. It slaps around and then settles down again. What is happening is you're flying over some point of un-even terrain and thus that's the result you see on a radar (or radio) altimeter, be it analog or digital.

 

If this were to happen close to the MAP, you would simply use the MSL altimeter and make your decision on that instrument.

Because 200ft ARL is actually quite a bit from the threshold, and the terrain there can be decieving for a radio altimeter.

 

I'm almost sure the answer to the following question is "no", but I'm asking anyway: Don't the "DH" on the chart precisely takes the surrounding terrain into account? So that when the aircraft is exactly on the glide-path and the radio altimeter indicates "DH", then the aircraft is where it's supposed to be? I'm asking because I *think* (not sure), that I've seen DH's that did not equal to "DA - TDZ elevation", so I thought that might be because of the surrounding terrain and the chart taking that into account. 

 

That or the airport installs a "virtual surface" for the radio altimeter, just like this:

 

 

Poor fella who lives right there... unlucky cat he is...lol

 

 

 

 

If the terrain descends, however... you would find yourself having 200RA alert later than you should. So you might think you are OK but actually bust minimums. That could end bad, if you had an accident or an incident.

 

A very good example of that is landing into runway 30 at Tenerife North, GCXO (the airport where the two 747s collided in 1977). If you fly the ILS, the terrain goes from sea level to 2000 ft in less than 4 nm.

 

 

I'm almost sure the answer to the following question is "no", but I'm asking anyway: Don't the "DH" on the chart precisely takes the surrounding terrain into account?

 

Depends on the charts. I am most familiar with LIDO, they have two values on them (three actually, with RVR or VIS). First line there is nominal DH, usually 50, 100, 200. Under that there is the corrected value you would use. Radio mins values denoted by RA. CAT II value of 108RA or 115RA or so, for example. For lower categories they are BARO mins, rounded up to nearest 10. 1390 for example.

I'll make a comment but I'm sure others be will able to offer their keen insights as well.

 

I will provide two answers. One for the real world and one for us flight simmers.

 

Real world response:

 

Well, being a CAT I ILS approach, that would imply it is a manually flown ILS approach. In this case, I will be doing a FD ILS approach and using A/T to control my speed. I will make my speed adjustments from the A/T knob on the MCP vs manually pulling and pushing the throttles around directly.

 

Reviewing the STAR (Stand Terminal Arrival Route) if there is one, I would try to determine if I am going to be able to fly the standard ILS procedures as called out in the Boeing ILS Flight Crew Training Manual (FCTM). Specifically I am trying to determine if I will be able to be at flaps 5 (and at flaps 5 min maneuvering speed) when I am on my localizer intercept heading. Or, due to the kind of arrival, if things are going to get busy in a hurry, I will opt to intercept the localizer at flaps 15 with my speed set accordingly.

 

Depending on the altitude I am intercepting the localizer at and what the ILS GS intercept altitude is and its fix location, I may elect to put the gear out a little early too. Just depends.

 

At this point, I don't need to press APP on the MCP because this is not an AP flown approach (it could be with an AP disconnect at DH).

 

At localizer capture I will set HDG to the inbound course.

 

(I like to be "all in" on the MCP when I'm on my localizer intercept heading as well. By this I mean I like to be out of LNAV and VNAV and directly on the MCP in HDG sel and ALT hold. It's just my preference. It's perfectly fine to hold on to LNAV for localizer capture, I just prefer to be out of LNAV/VNAV and "all in" on the MCP only).

 

So, back to the approach...so if I hold on the gear drop, I will wait for GS alive to select flaps 15, update the A/T speed accordingly, lower the gear and arm the speed brakes.

 

At GS capture I will select flaps 25, 30 and then 40 and adjust A/T speed for each selection to bleed down to Vref + 5. I like to land at flaps 40 but you may prefer flaps 30. I will then set the missed approach altitude in the MCP altitude window and call for the landing checklist.

 

At this point I will fly down the ILS following my FD command bars and waiting for my DH point (200 feet) to decide to land or execute a miss.

 

You probably have a pretty good handle how to make a manual landing?

 

I should also say I never fly an ILS raw data (no FD) approach...for an ILS I always use the Flight Director. Some carriers forbid flying a raw data ILS.

 

My response in regards to us flight simmers:

 

Since this thread was on CAT III autolands I will say this. I fly my PMDG 737NGX on any kind of CAT ILS there is; I, II or III. It works fine. I'm not sure if that is what you were looking for in an answer.

I'll make a comment but I'm sure others be will able to offer their keen insights as well.

 

I will provide two answers. One for the real world and one for us flight simmers.

 

Real world response:

 

Well, being a CAT I ILS approach, that would imply it is a manually flown ILS approach. In this case, I will be doing a FD ILS approach and using A/T to control my speed. I will make my speed adjustments from the A/T knob on the MCP vs manually pulling and pushing the throttles around directly.

 

Reviewing the STAR (Stand Terminal Arrival Route) if there is one, I would try to determine if I am going to be able to fly the standard ILS procedures as called out in the Boeing ILS Flight Crew Training Manual (FCTM). Specifically I am trying to determine if I will be able to be at flaps 5 (and at flaps 5 min maneuvering speed) when I am on my localizer intercept heading. Or, due to the kind of arrival, if things are going to get busy in a hurry, I will opt to intercept the localizer at flaps 15 with my speed set accordingly.

 

Depending on the altitude I am intercepting the localizer at and what the ILS GS intercept altitude is and its fix location, I may elect to put the gear out a little early too. Just depends.

 

At this point, I don't need to press APP on the MCP because this is not an AP flown approach (it could be with an AP disconnect at DH).

 

At localizer capture I will set HDG to the inbound course.

 

(I like to be "all in" on the MCP when I'm on my localizer intercept heading as well. By this I mean I like to be out of LNAV and VNAV and directly on the MCP in HDG sel and ALT hold. It's just my preference. It's perfectly fine to hold on to LNAV for localizer capture, I just prefer to be out of LNAV/VNAV and "all in" on the MCP only).

 

So, back to the approach...so if I hold on the gear drop, I will wait for GS alive to select flaps 15, update the A/T speed accordingly, lower the gear and arm the speed brakes.

 

At GS capture I will select flaps 25, 30 and then 40 and adjust A/T speed for each selection to bleed down to Vref + 5. I like to land at flaps 40 but you may prefer flaps 30. I will then set the missed approach altitude in the MCP altitude window and call for the landing checklist.

 

At this point I will fly down the ILS following my FD command bars and waiting for my DH point (200 feet) to decide to land or execute a miss.

 

You probably have a pretty good handle how to make a manual landing?

 

I should also say I never fly an ILS raw data (no FD) approach...for an ILS I always use the Flight Director. Some carriers forbid flying a raw data ILS.

 

My response in regards to us flight simmers:

 

Since this thread was on CAT III autolands I will say this. I fly my PMDG 737NGX on any kind of CAT ILS there is; I, II or III. It works fine. I'm not sure if that is what you were looking for in an answer.

Thanks for your time Ralph, much more enlightend now.

 

Cheers

So I the decision to use different categories of landing based on weather? Visibility? I realize it will also depend on what the airport is rated for, but can you make a hand flown CAT I approach on a runway rated for CAT III?

 

Thanks for your knowledge

So I the decision to use different categories of landing based on weather? Visibility? I realize it will also depend on what the airport is rated for, but can you make a hand flown CAT I approach on a runway rated for CAT III?

 

Thanks for your knowledge

 

Yes, it's the actual weather conditions, the airport will call it...meaning if the weather is down to CAT III minimums, they will officially set the airport at that level. This will engage and enforce those CAT III Hold lines on the taxi ways so ground traffic must now hold behind the solid double lines while waiting.

 

What this also means to us is that ONLY aircraft and crews that are qualified and current to do a CAT III autoland (or a CAT IIIa manual landing using the HUD as I've learned from this thread) will be landing until further notice.

 

As for you second question: in VFR conditions you can fly any ILS approach you want. Each approach plate has its own minimums and RVR values, so it really doesn't make sense to say can I fly a CAT I ILS on a CAT III ILS approach? You can just fly the CAT III ILS, period. Just fly it and adhere to its minimums criteria.

 

Now, again, I have to say: if the actual weather is poor and you're flying an ILS approach, then you must pick an ILS where you and your aircraft are legal to fly that ILS approach. All ATC will do is clear you for the approach. It's your responsibility to make sure your approach is legal...that's why they are paying you the big bucks 

I came across this neat video today which shows what Ralph taught us in the ground school course in action on a real 737(although they did a CATII, the same ideas apply). I think the two videos complement each other very nicely!

 

https://www.youtube.com/watch?v=Bm02l989PUw

I came across this neat video today which shows what Ralph taught us in the ground school course in action on a real 737(although they did a CATII, the same ideas apply). I think the two videos complement each other very nicely!

 

https://www.youtube.com/watch?v=Bm02l989PUw

 

Now that I watch that video, full autoland on an ILS CAT II, my question is:

 

When is autoland optional/mandatory/prohibited?

 

Ralph pointed out on his presentation that CAT I and II are manual landing only, while CAT III is autoland only.

 

Matt then said that when using the HGS, they can fly a CAT IIIa manually

 

On this video they do an autoland on CAT II

 

It's still not clear to me...

I came across this neat video today which shows what Ralph taught us in the ground school course in action on a real 737(although they did a CATII, the same ideas apply). I think the two videos complement each other very nicely!

 

https://www.youtube.com/watch?v=Bm02l989PUw

 

Very nice video indeed...!!! Thanks for sharing that...!!!

Now that I watch that video, full autoland on an ILS CAT II, my question is:

 

When is autoland optional/mandatory/prohibited?

 

Ralph pointed out on his presentation that CAT I and II are manual landing only, while CAT III is autoland only.

 

Matt then said that when using the HGS, they can fly a CAT IIIa manually

 

On this video they do an autoland on CAT II

 

It's still not clear to me...

 

Hi Jamie

 

I think the confusion still has to do with what is the weather conditions? Remember, if the weather is clear, you can do an autoland on any ILS and if it's not a CAT III ILS, then you have to carefully monitor the autoland. So, in other words, if the weather is clear, you can autoland using a CAT I or II or III ILS.

 

If the weather is down to actual CAT II or III minimums, then you must use the correct ILS approach plate, the crew must be qualified and current and the aircraft autoland must be certified and operational (no broken components) for the CAT II or III approach.

 

Yes, it is true that CAT I and II ILS approaches are pilot flown (we're talking actual wx minimums here) but don't forget that the FAA can allow carriers to conduct special ops such as Matt's airline: hand flying a CAT IIIa using the HUD. So, that's an exception but since reading that post from him, I've found carriers who can do the same thing. So, there is a standard but there are also exceptions.

 

I thought the video posted by Ryan was really good. I liked it, especially the captions. Since they were autolanding on a CAT II I assume the weather was relatively clear. I also noticed their ILS did not have DME. DME is a critical item for an ILS at low minimums so I'm guessing that the ILS approach they were shooting wasn't really a CAT II ILS but I guess there are always exceptions. I could not tell what kind of ILS that really was. I would need to know the airport and what runway they were landing on.

 

Jamie, I hope this helps.

I'm not sure if the discrep ever got resolved between the ILS CAT question, so I'll add in my input in an effort to put it to bed:

 

All ILS installations (in the United States) are categorized as CAT I, CAT II, or CAT III (to include a/b or SA, as appropriate).  When listed on charts, the "standard" category is CAT I.  As such, the specific verbiage "CAT I" is omitted, unless it is CAT I SA, where that verbiage is specifically appended.  CAT II and CAT III approaches also include the specific CAT II/III(a/b/c) designator as appropriate.  While there are "standard" values for the MDA/DA/MDH/DH for all of the various approaches, this should not be used to determine the category.  These values are adjusted to make the procedure more relevant to the specific airport, based on evaluations of the TERPS surfaces, available equipment, signal reliability/quality, and so on.

 

 

 

As far as "when is it okay to autoland," the answer is "it depends."

 

The basic answer is that it is prohibited (entirely - surprise!) for ILS at any time.  This is determined by the minimum altitude for AP use defined in the regs, which (for ILS) is any altitude below either the published AP max altitude loss plus 50' (IFR); or the higher of the published AP max altitude loss, or 50' (IFR).  The catch mentioned in that same section, however, is that it may be approved via company Ops Specs.  If the Ops Specs do not refer to CATs when setting up autoland conditions, then autolands can be made on an ILS, regardless of CAT.  It all depends on how the Ops Specs are written, which is all related to how clever your legal team is.

 

...welcome to Greyviation™.

 

One thing to remember, though, is that if it's not a CAT III approach, the equipment has not been tested, and is not being monitored, for signal quality or usefulness up to CAT III standards (meaning "signal quality to the ground").  This means that the LOC or glideslope could be inaccurate below a certain altitude (though the charts generally make note of this), among other things.  This could mean the aircraft will not track the signal properly all the way to the ground, which, as you could imagine, could be a big problem.

 

It's not that the equipment at the end of the runway is different.  It's that it's been evaluated to the standards set forth in the requirements for that CAT.  If you had an airport in the middle of an open prairie with an ILS, you could easily get it certified to CAT III standards (if you wanted to).  Start adding towers, trees, terrain, buildings, and anything that causes signal interference* in the area and CAT III certification becomes tougher, on that same equipment.  Because CAT II SA and CAT III are the only CATs where autoland is required (except in special authorizations with HUDS), they're the only ones with signal reliability up to the required standard for an autoland.  As such, if you would like to attempt an autoland on an aircraft that is approved via your company Ops Specs on any other CAT of installation, it is your own prerogative, but you should maintain extra vigilance to ensure the AP is tracking the LOC/GS accurately and appropriately, as the signal quality is not guaranteed for that operation.

 

*This could simply be the makeup of the ground below - ever see "Magnetic Disturbance of as much as X degrees exists at Y altitude in this area?" Check out the area just south of W99.  That's an example of natural interference.

 

 

 

The answer is . . . "BECAUSE WE DIDN'T HAVE THEM ON THE -200, DAGNABBIT! THE -200 WOULD STOP ON A DIME. CLAM SHELLS. . . JT-8D!"
 
Alaska is so good at standardization, we are standardized with planes we don't even have anymore.

 

My co-workers are all starting at me oddly for the random laughter that just came from my direction.  Thanks for that.  Hilarious...

Congrats. A must see!!!

Just thought I'd add this vid, as I liked it, and it's associated.

 

Thanks again Ralph, and please feel free to do a CAT I vid tut, if you have the time spare :-)

 

http://www.youtube.com/watch?v=sRV7f7IKdr4&feature=youtube_gdata_player

A CAT I is just a normal ILS approach, hand flown...so I'm not sure what I could add because there are a ton of those videos out there already...

 

 

A CAT I is just a normal ILS approach, hand flown...

 

Just to clarify, it's a normal ILS approach.  It can be coupled with autopilot down to the minimums specified in my earlier post, if desired.  You're absolutely right that it must be landed by hand, except in the cases mentioned in my earlier post as well.