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Old 10th Jun 2010, 16:09   #1 (permalink)
 
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CATlll "Fail Passive" approach

I'm looking at this statement and having trouble with the accuaracy. (B777)

If the NO LAND 3 message appears before the LAND 3 is annunciated on the PFD, it is an Advisory message. The aircrew should anticipate a LAND 2 fail passive approach and should adjust minimums accordingly. The minimums for a fail passive Category lll approach are typically set to a 50 foot Decision Height (DH) on the radio altimeter.

If anything I would imagine restting the RA upwards to say 100'?

What do make of this? Maybe I'm having a problem wrapping my head
around the CATlll "Fail Passive" concept. Seems like if you had aLAND 2 showing you would simply move up to CATll mins?
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Old 10th Jun 2010, 16:15   #2 (permalink)
 
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Unless I've got the wrong end of the stick here....
No LAND 3 refers to the number of autopilots...not the CAT of approach that you are attempting.
Therefore, LAND 2 means that you have 2 autopilots remaining, and can carry out a Cat 3A approach. ie 50 feet DH
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Old 10th Jun 2010, 16:42   #3 (permalink)
 
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Pretty much spot on, hunterboy, though it can indicate other failures than just one Autopilot channel inop. Land 2 means the aircraft is CatIIIA (typically a 50' DH) rather than CatIIIB (Anything down to NO DH.).

No Autoland is actually a reverttion to Cat I. There is NO failure of aircraft system that causes a revertion to Cat II.
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Old 10th Jun 2010, 18:11   #4 (permalink)
 
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What does fail passive mean?
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Old 10th Jun 2010, 18:27   #5 (permalink)
 
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In simple terms

Fail operational, you have redundancy

Fail passive you don't
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Old 10th Jun 2010, 18:31   #6 (permalink)
 
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Wizofoz' explanation btw. covers the 737 as well Only 2 autopilots so the NO LAND 3 message just means LAND 3 is not available, nothing about the autopilots available.
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Old 10th Jun 2010, 21:46   #7 (permalink)
 
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A previous post I added to another thread on this may be of use:

CAT3B fail passive
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Old 13th Jun 2010, 06:48   #8 (permalink)
 
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Of course, all this one channel failed business with triplex autoland systems was solved long ago, with a dual/dual fail operational autoflight system, developed by Collins Radio, and fitted to one quite noteworthy widebody jet transport aircraft.
TriStar....dual/dual from the beginning, forty years ago, this year.
Often admired, seldom imitated.
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Old 13th Jun 2010, 09:07   #9 (permalink)
 
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With fail active a single failure, usually below 400 feet, permits continuing the approach.

As to U.S. carriers with fail active you use an Alert Height (AH), which is usually 50 feet. You don't have to see anything at AH, just make sure there are no pertinent displayed warnings.

With fail passive there is typically a 50-foot DA, which means you have to have the required visual references by 50 feet.

The two are significant differences with RVR values near minimums.

These DA or AH authorizations and limitations are handled by Ops Specs, not by the approach chart.

Last edited by aterpster; 13th Jun 2010 at 12:59. Reason: word error
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Old 13th Jun 2010, 09:25   #10 (permalink)

 
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411A, you need to read up on the history of triplex autoland, and it didn't happen in the US.
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Old 13th Jun 2010, 09:29   #11 (permalink)
 
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411:
Quote:
Of course, all this one channel failed business with triplex autoland systems was solved long ago, with a dual/dual fail operational autoflight system, developed by Collins Radio, and fitted to one quite noteworthy widebody jet transport aircraft.
TriStar....dual/dual from the beginning, forty years ago, this year.
Often admired, seldom imitated.
I would agree. I flew the L-1011 as a F/O when it was in service about two years. Then, back to the 727 as captain. Several years later I was an early check-out on the 767-200. Flew it for a couple of years, then back to the L-1011 as captain. I did a lot of auto-lands in both types. And, several minimum RVR landings in the L-1011.

They were both very, very good at fail-active operations and auto-landing. But, my subjective view is that although the L-1011 did not have a guidance/redundancy edge over the 767, it did have a bit more aerodynamic stability because of the direct lift control (DLC).

I understand that Lockeed when to Collins/Lear and say, "Tell us what you want in wing configuration and flight control systems to assure we qualify for fail-active CAT III (Alert Height). Collins/Lear indeed got involved and had a lot to do with DLC being added to the design, as well as the configuration of the wing.
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Old 13th Jun 2010, 10:09   #12 (permalink)
 
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We operate according to 98% source data. The rest of our FCOM’s contain operator exemptions. In this chapter I can’t find any exemptions. From the excerpt below I can only conclude that you need to see LAND 3 for any form of CAT III approach. If you are not LAND 3 but LAND 2 the lowest limits are CAT II.

From FCOM I limitations.
CAT II Operations
• LAND 3 or LAND 2 must be annunciated.
• Prior to commencement of the approach, the EICAS messages SGL
SOURCE DISPLAYS, SGL SOURCE RAD ALT or SGL SOURCE ILS
may not be displayed.

CAT III Operations
• LAND 3 must be annunciated.
• Prior to commencement of the approach, 2 autoland status annunciators
and the autothrottle must be operative, and the EICAS messages SGL
SOURCE DISPLAYS, SGL SOURCE RAD ALT or SGL SOURCE ILS
may not be displayed.
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Old 13th Jun 2010, 15:00   #13 (permalink)
 
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Forget:
Quote:
411A, you need to read up on the history of triplex autoland, and it didn't happen in the US.
Do you have a reference for that history?
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Old 13th Jun 2010, 15:43   #14 (permalink)

 
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Quote:
Do you have a reference for that history?
As it's 'only' Wiki let me know which part of this you disagree with.

Autoland - Wikipedia, the free encyclopedia

Maybe this.

This led to the absurd situation for British Airways that as the launch customer for the Boeing 757 to replace the Trident, the brand new “advanced” aircraft had inferior all weather operations capability compared to the fleet being broken up for scrap. An indication of this philosophical divide is the comment from a senior Boeing Vice President that he could not understand why British Airways were so concerned about the Category 3 certification, as there were only at that time two or three suitable runways in North America on which it could be fully used. It was pointed out that British Airways had some 12 such runways on its domestic network alone, four of them at its main base at Heathrow.
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Old 13th Jun 2010, 16:01   #15 (permalink)
 
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Never underestimate the ability of a "vice president" to make foolishly ignorant remarks. However, I'm pretty sure the 767/757 was designed from the ground up around the CAT III capability, so I would not take this story as representative of Boeing's design philosophy.
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Old 14th Jun 2010, 13:01   #16 (permalink)
 
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"No Autoland is actually a reverttion to Cat I. There is NO failure of aircraft system that causes a revertion to Cat II".



May have misunderstood your statement here but there are numerous mechanical failures within the B777 & 787 that will produce a NO LAND 3 and thus a LAND 2.
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Old 14th Jun 2010, 14:18   #17 (permalink)
 
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LAND 2 just means you cannot fly a fail operational approach, but you can fly a fail passive one which is still CAT III, albeit CAT IIIa now.
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Old 14th Jun 2010, 14:48   #18 (permalink)
 
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With regard to the NO AUTOLAND scenario, the FAA has approved Operations Specifications permitting a manually flown CAT II approach and landing...indeed, that was the way CAT II ops were originally conducted. Hence, a failure leading to a NO AUTOLAND annunciation could "revert" to a CAT II capability. This obviously depends on the operator's certification and procedures, training, etc.
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Old 14th Jun 2010, 19:26   #19 (permalink)
 
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Thanks Guys!
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Old 15th Jun 2010, 13:33   #20 (permalink)
 
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Ok guys,
The thread started with a question about the LAND 2 status in relation to landing minima for a Boeing 777. I quoted from our FCOM.

LAND 3 = CAT 3 (whatever version).
LAND 2 = CAT 2.

Now people are referring to NO AUTOLAND and still being CAT 2. The excerpt below from the Boeing 777 shows that with weather conditions below CAT 1 you need perform an automatic landing.

NO AUTOLAND = CAT 1.

Boeing FCOM 1 – Limitations
Automatic Landing

*The maximum glideslope angle is 3.25 degrees.
*The minimum glideslope angle is 2.5 degrees.
*Automatic landings can be made using flaps 20 or 30, with both engines operative
or one engine inoperative.
*With weather conditions below published CAT I minima, an automatic landing is
compulsory.
*Automatic landing under CAT III weather conditions is not allowed on runways
narrower than 45m in width.

If anybody has other limits in their FCOM’s for the Boeing 777 I am very interested in reading about them.
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