CAT 3 B with DH
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CAT 3 B with DH
Anyone who could shed light into my question under which conditions we would actually fly a CAT 3B approach with DH ? Is it only a legal requirement for the SIM or are there cases where application of a DH during CAT 3B is imperative ?
Thank you !
Thank you !
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Thanks for your answer JammedStab !
So it's because of minima established for certain airports not able to offer a NO DH CAT 3B approach ?
What is the actual reason for Paris, that I'am obvously not aware of ?
Thanks !
So it's because of minima established for certain airports not able to offer a NO DH CAT 3B approach ?
What is the actual reason for Paris, that I'am obvously not aware of ?
Thanks !
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It's twelve years since i've flown a 3B aircraft but in our company it used to be a blanket 15ft/125m for France and 0/75m for the rest. I always got the impression that it was a French rule.
It's also an 'American thing'.
A quick look through a major EASA airline's manuals reveals that Los Angeles LAX, Chicago ORD and New York JFK do not allow Cat3B No DH, whereas they do allow Cat3B with a DH.
However, Denver DEN does allow it!
A quick look through a major EASA airline's manuals reveals that Los Angeles LAX, Chicago ORD and New York JFK do not allow Cat3B No DH, whereas they do allow Cat3B with a DH.
However, Denver DEN does allow it!
Was told years ago that the French (perhaps it was the pilot unions) just couldn't accept that zero DH operations were acceptable or possible so they insisted on having a number to work to and its stuck, no idea if its true but sounds plausible. Would you actually fly to it or land anyway is another matter, think I know what I would do.
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A CATIIIb designation may have no decision height, or may have a decision-height that is 50ft or below. A CATIIIc designation has no decision height and no visbility requirements.
It is the individual carrier's OpSpecs and on-board equipment that determines approach capability, (a, b or c), not the regulator or ATC. Essentially there is no difference in ground equipment or runway holding position between CATIII a, b or c approaches.
It is the individual carrier's OpSpecs and on-board equipment that determines approach capability, (a, b or c), not the regulator or ATC. Essentially there is no difference in ground equipment or runway holding position between CATIII a, b or c approaches.
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In the States, runways are certified as either Category III or not. The aircraft systems and operator programs are certified as either fail passive or fail operational, and are limited to some point on a ladder of decreasing RVR values as the program develops. While there is a definition of CAT IIIA and IIIB still in the advisory material, the only people really still using this terminology are the Jeppesen folks...over here, at any rate.
The only technical reason for a DH, on any approach, is the requirement to use visual references. For CAT II approaches, this means that the lighting must be adequate to manually maneuver the aircraft into the touchdown zone. I realize that few operators allow manual CAT II landings anymore, but that is what the visual references are predicated on. Note that in the States, we now have waivers allowing CAT II approaches with diminished lighting as long as we autoland...which sort of restates the preceding point.
For CAT III fail passive approaches, the visual references are only necessary to confirm the aircraft's position in space at 50 feet. This provides the redundancy required for an autolanding that is otherwise unavailable because you are only using two autopilots, or two channels of one autopilot. Essentially, you need to see green TDZ lights on the left and green TDZ lights on the right.
I have no clue why the French require a visual reference at 14 feet; I see that Airbus recognizes this in the document of theirs I found on Skybrary. They say for such low DHs, you only need to see one centerline light. Presumably it needs to be right in front of you, and hopefully it is a centerline light!
However, silly as it may seem, one would have to investigate the construction and maintenance of their ground-based systems, i.e., localizer, system monitors, protections from interference, etc..before drawing any conclusions. The FAA AC 120-28D defines it thus:
The only technical reason for a DH, on any approach, is the requirement to use visual references. For CAT II approaches, this means that the lighting must be adequate to manually maneuver the aircraft into the touchdown zone. I realize that few operators allow manual CAT II landings anymore, but that is what the visual references are predicated on. Note that in the States, we now have waivers allowing CAT II approaches with diminished lighting as long as we autoland...which sort of restates the preceding point.
For CAT III fail passive approaches, the visual references are only necessary to confirm the aircraft's position in space at 50 feet. This provides the redundancy required for an autolanding that is otherwise unavailable because you are only using two autopilots, or two channels of one autopilot. Essentially, you need to see green TDZ lights on the left and green TDZ lights on the right.
I have no clue why the French require a visual reference at 14 feet; I see that Airbus recognizes this in the document of theirs I found on Skybrary. They say for such low DHs, you only need to see one centerline light. Presumably it needs to be right in front of you, and hopefully it is a centerline light!
However, silly as it may seem, one would have to investigate the construction and maintenance of their ground-based systems, i.e., localizer, system monitors, protections from interference, etc..before drawing any conclusions. The FAA AC 120-28D defines it thus:
A Decision Height is applied to all Fail Passive operations and is specified at certain locations where fail operational minima is authorized. For Category III, a Decision Height is usually based on a specified radio altitude above terrain on the final approach or touchdown zone. The Decision Height is established to assure that prior to passing that point the pilot is able to determine that adequate visual reference exists to allow verification that the aircraft should touch down in the touchdown zone.
I have a recollection that some very low DH "Cat3B" operations used a DH purely for confirmation of sufficient visibility to control the aircraft laterally after touchdown, in the event of roll-out guidance (either autopilot or with the "barber's pole" glareshield mounted "Para-Visual-display) failure. It was not a DH of the conventional kind requiring assessment of position and rate of change of position. The actual landing had to be automatic. However I can't supply chapter and verse on that.
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It's also an 'American thing'.
A quick look through a major EASA airline's manuals reveals that Los Angeles LAX, Chicago ORD and New York JFK do not allow Cat3B No DH, whereas they do allow Cat3B with a DH.
However, Denver DEN does allow it!
A quick look through a major EASA airline's manuals reveals that Los Angeles LAX, Chicago ORD and New York JFK do not allow Cat3B No DH, whereas they do allow Cat3B with a DH.
However, Denver DEN does allow it!
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I think the idea of having a DH for CAT 3B came about for some XAA's thinking about the approach ban. If the RVR is at or above the required when passing the OM you can continue to DH. If, after OM, the reported RVR falls below minima you can continue to DH for a 'look see'. If there is no DH it means you can land with no decision to be made. I heard some felt uncomfortable with not having to make a decision. Having said that, a DH of 14' gives no time to decide. By the time you've thought about it the wheels have made contact and the speed brakes are out. But for a lawyer there was a point to make a decision. Fudge, fudge.
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If, after OM, the reported RVR falls below minima you can continue to DH for a 'look see'. If there is no DH it means you can land with no decision to be made.
Not sure where you looked, but I just looked at the CAT II/III plated for LAX and ORD, and none of them had a DH associated with any of the CAT III approaches.
It must be an opspecs thing. I live in Denver and have been based here and LAX well as flying into ORD hundreds of times in A320, 767, and 757. We used an Alert Height of 50 feet for Cat III approaches. It was not a decision height and there was no requirement to see anything prior to touchdown.
Last edited by Rick777; 21st Feb 2016 at 03:30.
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Answers are in FAA AC120-28D
The answers to virtually all these Cat III, Cat IIIA and Cat IIIB, and DH and No-DH questions are contained in FAA AC120-28D. There are some more recent minor exceptions and subtle twists, per issuance of more recent Op-Specs, such as for Alaska Airlines' Hybrid Cat III Ops, using both autoland, and the HUD AIII Mode to monitor the AP.
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"It must be an opspecs thing."
Yes, it is indeed Ops-Specs. ATC cannot issue a clearance for a "CATIIIb" approach; "CATIII" approaches are being conducted, period. The a, b or c level is an individual carrier specification.
Yes, it is indeed Ops-Specs. ATC cannot issue a clearance for a "CATIIIb" approach; "CATIII" approaches are being conducted, period. The a, b or c level is an individual carrier specification.
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Very nice thread guys...
Let me ask you something. For B-737 Ng, the FCTM states that, for fail operational autoland approaches, above Alert Height if a mode change occurs e.g. from Land 3 to Land 2 or to No Autoland, set new minima or go-around. At least I understand it that way.
Pretend that, for a CatIII B approach after self test Land 3 announciated but above 200' AH it changed to LAND 2, shall we set a new minima e.g. CAT III A minima of 50' ?
Thank you veryu much indeed.
Let me ask you something. For B-737 Ng, the FCTM states that, for fail operational autoland approaches, above Alert Height if a mode change occurs e.g. from Land 3 to Land 2 or to No Autoland, set new minima or go-around. At least I understand it that way.
Pretend that, for a CatIII B approach after self test Land 3 announciated but above 200' AH it changed to LAND 2, shall we set a new minima e.g. CAT III A minima of 50' ?
Thank you veryu much indeed.
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Sundown,
In a purely technical world you could do that. However, I would almost guarantee that your company procedures or authority approvals, whatever form that might be in, will disapprove. The last thing anybody wants you doing at 500 feet is changing bugs, etc. Further, a fail-passive approach has different ground equipment requirements, in terms of touchdown zone lighting, RVR values, etc. It is certainly possible that all of those criteria are satisfied, and you could in theory brief the approach for the contingency you have suggested...but everyone I have worked with prefers the idea that when it drops out of LAND 3, you go around, assess, re-brief, and fly the fail-passive approach with LAND 2.
Assuming of course that you have enough gas and that the guy having the heart attack says he can last another 20 minutes...
In a purely technical world you could do that. However, I would almost guarantee that your company procedures or authority approvals, whatever form that might be in, will disapprove. The last thing anybody wants you doing at 500 feet is changing bugs, etc. Further, a fail-passive approach has different ground equipment requirements, in terms of touchdown zone lighting, RVR values, etc. It is certainly possible that all of those criteria are satisfied, and you could in theory brief the approach for the contingency you have suggested...but everyone I have worked with prefers the idea that when it drops out of LAND 3, you go around, assess, re-brief, and fly the fail-passive approach with LAND 2.
Assuming of course that you have enough gas and that the guy having the heart attack says he can last another 20 minutes...
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LAND 3 to LAND 2 reversion response
The answer depends both on company policy and Op-Spec approval.
That is the reason why some operators elect to simply set the RA bug at 50' HAT (or equivalent, for the specific SIAP, underlying terrain, and TDZ) and then for a LAND 3 Reversion to LAND 2 simply convert use of a (pre-briefed) Alert height of 50', instead to a revised DH of 50', with no need for any bug changing, ...and only the RVR limits being adjusted, as needed for the new minima (which is also pre-briefed).
That technique and procedure facilitates the ability to continue the approach, when WX may be deteriorating, and avoid an unnecessary MAP and ~15 minutes of more flying, while snow is accumulating and mu is decreasing, or the fog is getting worse.
Bottom line is that it is what the operator's policy is, that sets the response. It depends on what the operator is training to, and what have they applied for, and what do their Op-Specs permit.
Again see FAA AC120-28D (for Cat III) and AC120-29A for similar issues with Cat I and Cat II use of LAND 3 and LAND 2 modes.
Note: Similar questions can arise for various aspects of using AIII mode with a HUD, particularly with respect to known momentary anomaly annunciations due to confirmed temporary ILS beam anomalies (also note with GLS there are virtually NO beam anomalies ever.... GLS is simply amazing to see how much better it is than using an ILS for approach).
That is the reason why some operators elect to simply set the RA bug at 50' HAT (or equivalent, for the specific SIAP, underlying terrain, and TDZ) and then for a LAND 3 Reversion to LAND 2 simply convert use of a (pre-briefed) Alert height of 50', instead to a revised DH of 50', with no need for any bug changing, ...and only the RVR limits being adjusted, as needed for the new minima (which is also pre-briefed).
That technique and procedure facilitates the ability to continue the approach, when WX may be deteriorating, and avoid an unnecessary MAP and ~15 minutes of more flying, while snow is accumulating and mu is decreasing, or the fog is getting worse.
Bottom line is that it is what the operator's policy is, that sets the response. It depends on what the operator is training to, and what have they applied for, and what do their Op-Specs permit.
Again see FAA AC120-28D (for Cat III) and AC120-29A for similar issues with Cat I and Cat II use of LAND 3 and LAND 2 modes.
Note: Similar questions can arise for various aspects of using AIII mode with a HUD, particularly with respect to known momentary anomaly annunciations due to confirmed temporary ILS beam anomalies (also note with GLS there are virtually NO beam anomalies ever.... GLS is simply amazing to see how much better it is than using an ILS for approach).