CAT III minima

[nick14]

Morning all,

Im getting myself confused with CAT III minima. In my ATPL books i have found numerous references to the legal minima but they differ.

CAT IIIa - DH less than 100' or no DH (in Ace the tech. pilot int it says 50') and 200m

CAT IIIb - DH less than 50' or no DH and less than 200m but more than 75m

CAT IIIc - (never used commercially) No DH and No RVR

Now forgive me for being silly but arnt the IIIa/b a little similar. as you could be operating IIIb with a DH of 75' but you could also be operating IIIa :confused:

is it the RVR that is the deciding factor.
Many thanks
Nick

[nick14]

Just realised that you cannot be operating IIIb with DH of 75'.:O

The rest of my question still stands tho.

Thanks
Nick

[Engineer]

If you need the official definition then look in EU Ops (http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2006:377:0001:0175:EN:pdf) Appendix 1 to OPS 1.430 Aerodrome Operating Minima paragraph (c) Precision approach :D

[Fab66]

Hello Nick,

CAT III A => RVR 200m or greater DH <100ft but >50ft
CAT III B => RVR 75m or greater no DH or DH <50ft

Hope this help

FAB

[nick14]

great stuff thanks guys,

Nick

[BelArgUSA]

While there is NO DH for Cat.III operations you see "Alert Height" sometimes mentioned.
It is not published in CAT.III minimums, It is a "company procedure".
xxx
Right or wrong, I generally say Cat.IIIa has a AH of (about) 50 ft above TDZ.
And for Cat.IIIb, a AH is (about) 35 ft above TDZ.
That is for a 747-200... Some were Cat.IIIa. None were certificated Cat.IIIb.
We discontinued Cat.IIIa... Company only does Cat.II minimums.
xxx
:)
Happy contrails

[Wizofoz]

Bel,

Errr.... No.

CatIIIa most definatley DOES have a DH of not less than 50feet.

Alert height is not a "Company procedure", it is a certification requirement for catIII operation. It is the height below which a fail operational system will continue to a landing if one system fails.

On the 777 it's 200 feet. below this all but a few alerts are inhibited as the aircraft is certified to land after the failure of most single systems.

[BelArgUSA]

Well, it looks like we (again) do things differently...
:)
Happy contrails

[BelArgUSA]

We discontinued Cat.IIIa operations in 2002.
xxx
It required Autopilots A, B and C operating and Autoland.
"Decision" to land or missed approach was made at "Alert Height" 50 ft.
All I recall, is that we needed 200 (or 250?) meters RVR, there was no DH.
The planes were equipped with LRCU as required for Cat.IIIb., but no 747 Classic was ever Cat.IIIb.
xxx
And for Cat.II requires 2 autopilots to operate, for 100' DH.
If only 1 autopilot operating, our Cat.II increased and becomes 150' DH.
:ok:
Happy contrails

[Henry VIII]

is it the RVR that is the deciding factor.In EU-OPSLand yes.
e.g.
rvr 300, OVC 50ft >>> cat 2
rvr 100, OVC 1000 >>> cat 3b

[safetypee]

Historically there have been differences between CS and FAR, but recent efforts have been made to harmonise these regulations (AC 29).
Minima for low visibility operations are (have been) a combination of the aircraft equipment fit and certification, the operational requirements including visibility, and the standard of ground aids / lighting.
The altitude element can be related to the installed equipment and aircraft performance, from which the visibility follows and usually has to consider cockpit cut off angle.

JAR-OPS 1 attempted to rationalise many different European operational interpretations, including those based on the valuable ECAC doc 17 and the UK CAA fog model. The resultant regulations, IMHO, are a collection of the lowest standards which everyone can now subscribe to without much consideration of some of the hazards, e.g. auto Cat2, DH 100, is allowed to continue to 80ft in reduced visibility, but the new regulation fails to address what action to take if the autos fail between 100ft and 80ft – the visibility now being less than that previously agreed for manual landing.
Alternative, successful fuzziness in the regulations is seen in the European Super Fail Passive operation – Cat IIIa 50ft DH, in 150m RVR.
Then there are debates about ‘see to land’ (auto / manual), and ‘see to verify’ (auto Cat IIIb AH).

[Fab66]

Alert Height definition:

An Alert Height is a height above the runway, based on the characteristics of the aeroplane and its fail-operational automatic landing system, above which a category III approach would be discontinued and a missed approach initiated if a failure occured in one of the redundant parts of the automatic landing system, or in the relevant ground equipment (ICAO). :ok:

FAB

[bob21rk]

the only reason why they dont say straight-forwardly that catIIIb is minimum 50' is because it is a jeppessen classification. so you can have an airport fixing its cat IIIb minimum at 40' and it qualifies. however the minima, i feel are the deciding factor because catIIIa is either 100' or no DH at all and the others follow suit.

[Wizofoz]

NO,

CatIIIB less than 50' or no DH

CatIIIA less than 100', not less than 50'

Cat II less than Cat I, not less than 100

Regulaotory, ICAO catagories, nothing to do with Jepps.

[bochos]

please answer me what is the definition of alert height is trying to safegurd. i am trying to figure out the link. what the regulator had in mind when creating the definition. please answer me cause am desperate to know

[JABBARA]

What I know:

Alert height is a result of probability calculations for Fail Operational Approach and Autoland systems.

Simply a mathematical result so that with the redundancy of systems of a particular type of airplane, during the period of time from the time of crossing this height to completing the approach and landing, the subsequent failures of required systems are exteemly remote probability (below a threshold probability value).

That is all.

Below this altitude techinically nothing changes in the plane, however some extra warning systems are armed (or should be already armed -for example AUTOLAND light on AIRBUS-) to alert the pilot for the odd cases which this extreemly remote probability is breached

[bochos]

thank you much sir,
some other peropheral q's:
Alert height only applies when fail operational mode is announced on fma despite you are on cat 3 a approach?
Alert height for a320 is 100ra. is this the lowest possible AH or it could be lowered down to cat 3a minima of not less than 50ft?
Thank you very much for your help

[JABBARA]

Hi Bochos,
Alert height only applies when fail operational mode is announced on fma despite you are on cat 3 a approach?

Answer: Yes, regardless what minima you are flying to (even CAT 3A) if your system is capable to be Fail Operational (for Airbus when CAT 3 DUAL displays on FMA), in fact Alert Height is applicable. For CAT 3A minimum required system is Fail Passive system. However if your airplane is capable to fly Fail Operational, of course it is preferable to fly the same approach with Fail Operational system (that is why we are always engaging 2 A/P for even CAT 3A Approach in Airbus). As doing this, we are using the extra benefit coming with Fail Operational system (like Alert height)

Alert height for A320 is 100 RA is this the lowest possible AH or it could be lowered down to cat 3a minima of not less than 50ft?

For A 320, 100 RA is the maximum available AH, not the minimum. 100 RA is the approved altitude where above this altitude the required probability can not be achieved.

The following is an extract from Getting The Grips with CAT 2-3 (airbus)

The AH is only linked to the probability of failure(s) of the automatic landing system. Operators are free to select an AH lower than the AH indicated in the AFM but not a higher value. Airbus procedures include both AH and DH concepts for all Fail-operational (see later) Category III operations.


Consider like this, as a pilot I would like to sit in the flight deck of an airplane type so that the approved AH is as high as maximum. Because this means, I am sitting in the flight deck of a more reliable airplane. Further explanation: As the AH is higher, the duration passing from AH to completing App and landing is longer, consequently the airplane systems are so reliable, even at this longer period, the failure probability is still below threshold value.

Practically flying CAT 3A (lets say to DH 50 RA) with Fail Ops system and your AH is 100 RA, below 100 RA continue to land unless the designed warning system is triggered (e.g AUTOLAND light for A 320) and provided visual requirements is achieved by the time of reaching 50RA.

[Engineer]

It is interesting how the Atlantic Ocean divides opinions here is the definition taken from FAA CFRs

Category IIIA operations, an ILS approach and landing with no decision height (DH), or a DH below 100 feet (30 meters), and controlling runway visual range not less than 700 feet (200 meters).
Category IIIB operations, an ILS approach and landing with no DH, or with a DH below 50 feet (15 meters), and controlling runway visual range less than 700 feet (200 meters), but not less than 150 feet (50 meters)

EU Ops states
Category III operations are subdivided as follows:
(i) Category IIIA operations. A precision instrument approach and landing using ILS or MLS with:
(A) A decision height lower than 100 ft; and
(B) A runway visual range not less than 200 m.
(ii) Category IIIB operations. A precision instrument approach and landing using ILS or MLS with:
(A) A decision height lower than 50 ft, or no decision height; and
(B) A runway visual range lower than 200 m but not less than 75 m.

Don't you love semantics :{ looks like BelArgUSA was right. Another interesting fact that highlights differences in approach to aviation safety is the slow response time for EASA to implement the extension of ETOPS to 3 and 4 engine aircraft which the FAA did last year

[bochos]

Dear jabbara, saludos...
Many thanks... your words are falling in place in my head with accuracy lighting the dark spots and making things clear in logical manner. They sound more than some of cpts knooww...
Anyways...
AH is applicable whenever Fail Operational is announced regardless of approach. MFGS is frozen at AH thus the Fail operational mode is safegurded by the A/c s ability to cope with any single faileyre.
When is it "armed"? Is it "armed" when dual is announced on fma or at 100ra? What happens if you have fail passive, is fmgs still frozing passing 100ra or is not? from what i understand , sigle operational is not safegurded from AH thus it should not be armed....

As 100ra is the max AH and not the minimum (i now completly understand why) then, why should opperators change it to any lower value? what extra safety could be acheived with fail operational mode? below the nominal AH fmgs is frozen, duall is safegurded, a/c is able to cope with faileure, what else is for operator to lower AH value? Am i missing nything?

I am reading the A320 GTGRIPS manual and thats why all these questions were generated.... am just half way ... am sure more will be to discuss as i read through ... thank you very very much ...
stick around dont desapear now.... : )
bochos

[avionneta]

hi bochos,
you're on the right track. good way to get several thruths right & wrong !
alert height has nothing to do with a kind of mode that would arm and engaged, freezing some devices ... like the land inhibit for some failures, or ILS lock below 700 ft.
it's rather a decison point (sama concept as V1 for take off) that helps the pilot in a CAT III b having a failure at very low height. if it is at or less than 100 ft height, he will disregard the failure until aircraft stopped on the runway since he knows the aircaft will be able to complete the autoland safely (except a second failure affecting automatisms just after (the first being as well in relation to autoland equipements. bad luck !) or the red autoland warning)
see you
cyrille

[cortilla]

I Understand things slightly more operationally in a question of certification. Maybe i'm wrong, but you live and learn.

Cat IIIa 50'/200m so on the roll out the captain can keep the aircraft on the centreline using rudder control as soon as the a/c completes the flare, autopilot has to come out, as there is no rudder control by the autopilot. If you leave it in the autopilot tries to maintain the centreline using aileron, which on the ground is useless

cat IIIb the autopilot can control the rudder and so can maintain the centreline during roll out. Hence lower minima.

cat IIIc the autopilot can complete the roll out and taxi the aircraft to the stand. (which at the moment is impossible as there is no suitable guidance systems). if it's 0/0 you can't see so you can't manually taxi.

I'm willing to be corrected, but this is how i understand the essential differences between the 3 options. I've only ever flown cat IIIa (i really don't like it btw, very unnerving).

[avionneta]

cortilla,
sorry you're wrong
from cat II to CAT III A included you can use or not the roll out capability
for CAT III B, you MUST use it

[bochos]

Dear C, saludos...


AH is applicable whenever Fail Operational is announced regardless of approach. MFGS is frozen at AH thus the Fail operational mode is safegurded by the A/c s ability to cope with any single faileyre.
When is it "armed"? Is it "armed" when dual is announced on fma or at 100ra? What happens if you have fail passive, is fmgs still frozing passing 100ra or is not? from what i understand , sigle operational is not safegurded from AH thus it should not be armed....

As 100ra is the max AH and not the minimum (i now completly understand why) then, why should opperators change it to any lower value? what extra safety could be acheived with fail operational mode? below the nominal AH fmgs is frozen, duall is safegurded, a/c is able to cope with faileure, what else is for operator to lower AH value? Am i missing nything?

I am reading the A320 GTGRIPS manual and thats why all these questions were generated.... am just half way ... am sure more will be to discuss as i read through ,
stick around :ok::ok:... : )
bochos