CAT 3 B with DH

[RvB]

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 !

[JammedStab]

Paris, France. CAT IIIB DH=14 feet. Anybody know why.

[RvB]

Paris, France. CAT IIIB DH=14 feet. Anybody know why.

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 !

[Flap40]

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.

[Fursty Ferret]

As Flap40 says, it's a French thing. No idea why.

[eckhard]

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!

[Max Angle]

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.

[FDMII]

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.

[Mansfield]

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:

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.

[slast]

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.

[Check Airman]

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!

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.

[RAT 5]

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.

[Denti]

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.

Apparently there are even weirder interpretations of that rule. The local CAA where i work apparently believes if there is no DH you cannot continue to the DH since it doesn't exist and therefore anytime the RVR drops below 75m after passing the OM or an equivalent fix, a go around is mandatory. For france we used a blanket 20ft DH for airbii and 50ft for Boeings. But apparently the french have changed their way and we can now use the normal no DH.

[eckhard]

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.

I looked at the 'Company Specific' minima page for 24R and 25L. On the actual Lido approach charts it gives minima for Cat1 and Cat2. For Cat3 it says, 'Company' and then you have to refer to the Company Specific page. I guess it's an Ops Specs thing but still curious as to why Cat3B No DH would be allowed in a company's Ops Specs for DEN and not for LAX, given that the capability exists at both airports?

[Rick777]

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.

[7478ti]

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.

[FDMII]

"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.

[_Sundown_]

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.

[Mansfield]

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...

[7478ti]

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).

[JammedStab]

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! 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.

Time to make some clarifications in this thread. The post by Ekhard was not written clearly, but I interpret it as saying that LAX and ORD do not have a CAT III approach with a DH but EASA allows CAT III with DH. But then the same post says that Denver allows CAT III with DH. I checked the Denver charts in my Jeppesen manual and I did not see this at all. However, keep in mind that we do not all get the same approach plates from Jeppesen, so if anybody has different, please post. But, I suspect that the CAT III DH thing is only an EASA thing.

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.

I think this CAT II landing approval without autoland may be what Horizon Air uses on their Dash-8-400 out in Seattle which subject to confirmation, is also, I believe, done with manual throttle. Concerning the requirement for autoland when doing a CAT II reduced visibility approach, this is not accurate. The ops spec I have says that autoland or HUD to touchdown is required.

For france we used a blanket 20ft DH for airbii and 50ft for Boeings. But apparently the french have changed their way and we can now use the normal no DH.

We still have a DH of 14 feet. But, I am reading that from a company manual(which is always subject to being out of date), not official French CAA documentation.

I looked at the 'Company Specific' minima page for 24R and 25L. On the actual Lido approach charts it gives minima for Cat1 and Cat2. For Cat3 it says, 'Company' and then you have to refer to the Company Specific page. I guess it's an Ops Specs thing but still curious as to why Cat3B No DH would be allowed in a company's Ops Specs for DEN and not for LAX, given that the capability exists at both airports?

This appears to be different than Jeppesen charts I have which show CAT IIIA or B minima for airports in the US. In EU, they only show CAT IIIA and in that case, a company specific page has to be referenced to see if there is even CAT III approval and for the CAT IIIB minima.

[quote=Rick777;9276617]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

[JammedStab]

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' ?



We continue. There seems to be different methods on what to do. But 50' RA can be pre-set and blanked on my aircraft type. So, if this happens prior to the FAF, reset the appropriate switches to 50' RA. If it happens beyond the FAF, the captain will simply say something such as "Fail-passive, RA 50, call 100 to minimums and minimums" with no switches being moved.

So all the F/O has to do for this is look at the RA and make the appropriate calls at 150 and 50 feet.

[7478ti]

This is all well explained in FAA AC120-28D (issued 13 June , 1999).

See section 4.3 of the AC in particular, reference use of an AH vs. a DH, for Fail-Op versus Fail-Passive. It also matters whether with or without rollout capability (e.g., note the original triple channel SPZ-1 B747s had FAIL-OP capability, but NO rollout system even installed [thus the Op-Spec visual confirmation requirement before TD], ...until later rollout systems were added via the "rollout special condition" which was used for their initial certifications.

Derek Helmore (UK CAA inspector) and I (for FAA) first sorted out the use of Fail Op and Fail Passive systems for Cat III, with Fail Op using only an alert height [and no need any more for a (low) DH] many decades ago, back when we were negotiating TWA's L1011 minima into the UK, ...versus Concorde minima to be used into KJFK and KIAD... as well as when we later wrote the first drafts of ICAO Doc 9365AN/910 (ICAO Manual of All Wx Ops).

Further we (the FAA/JAA AWO HWG) addressed addressed these subjects again extensively, over the decade of the '90s, before and leading up to issuing the [somewhat] harmonized revised versions of AC120-28D and AC120-29A, when they were published. This was also the period when we [the AWO HWG] globally dropped any further used of the concept of MABH.

Bottom line is that [under US rules] for LAND3 mode [i.e., Fail Op], an alert height is typically used [usually set at either 100' HAT or 50' HAT], and no DA(H) is necessary. For Fail passive systems and ops [i.e., LAND2 or equivalent] a DH is applied (with some minor exceptions for certain specific irregular terrain airports where an IM or DA may still apply), primarily to accommodate the possibility of a fail passive AP disconnect.

A minor special case has evolved recently, using AC120-28D (section 5.8) provisions for a "Hybrid System", by combining use of an autoland system, monitored with a suitable AIII mode capable HUD. Per the AC, this combination can theoretically be considered as a Fail-Op system, and used with an AH [and without a DH] if AP LAND 3 mode is used as baseline, ...or used with a low DH, if the AP mode used is LAND 2 or equivalent. In either case, the AP is backed up by a suitable AIII capable HUD, for the [contingency] continuation case, or balked landing GA case.

[_Sundown_]

Thank you very much for your feedback...

[7478ti]

That's also why we dropped MABH way back in the '80s.

Low DHs below 50' HAT (e.g., 15 ft), where you're below the adjacent taxiway tail heights, and obstacles "fixed by their aeronautical purpose" still make no sense at all. To get below 50' HAT one needs to be sure you're over the TDZ, period. Further, the aircraft are (required) assured to still have safe characteristics in the event of an inadvertent TD in the event of initiation of a low altitude GA.

That's why the AWO HWG long ago agreed that MABH is irrelevant (and JJ LaBlonde, Jacques Rosay, and Gerard Marin were each there for the deliberations), and was not needed. Further, applying any low DH below 50' HAT to any Fail Op A/L was simply an unnecessary distraction at a critical time in flare, ..and that to get below 50' HAT one ought to be Fail-Op or equivalent anyway.

The only few exceptions to this day, were the special cases using a Fail-Op system without a rollout system installed (e.g., some early B747s), which required confirmation of a safe TD and adequate visibility for the initial transition to rollout, ...before committing to a TD,... Or the more recent case of a "Hybrid" Fail-Op system situation, using HUD AIII mode (with reversion rollout capability) to monitor an AP FP autoland as the primary means of control.