Yet another one: Autoland malfunction

[Guest TheJones]

Here is another tricky challenge:You are on final, autoland CAT3b approach without any visual cue.when descending through 110 feet, you get the "NO LAND3" warning.what will you do?

[Guest Mark McG]

Perform a go around - Even though you may touchdown breifly while executing this manouever.

[Guest HPSOV]

Lets see if I can stuff another one up ;-)For a CatIIIb approach we use an alert height of 100ft. Above alert height you are able to go-around. However, if LAND 2 were still displayed (as it would be if NO LAND 3 was displayed) you have the option of continuing the approach but reverting to CatII minima. CatII minima being not less than 100ft, and being at 110ft you are basically in the position that if you are visual you can continue, if you are not visual you go-around.For a failure below alert height (100ft) you continue the approach regardless. The only thing you go-around for below 100ft is a NO AUTOLAND indication.However am I correct in thinking that the NO LAND 3 indication is inhibited below 200ft anyway? so the above situation wouldn't be possible?

[Guest Mark McG]

if you were to go around from the approach at 100ft, would the mains contact the runway?

[Guest HPSOV]

Fairly unlikely unless you copped a bad gust of wind or the autopilot was asleep (assuming its an auto-coupled go-around).There is a table in the performance manual that lists the expected altitude loss after an automatic go-around. From 50ft they say you will drop 39ft. From 10ft you'll drop 9ft. So by that even at 10ft you wouldn't touch the runway! However this would have been done by test pilots under ideal conditions I imagine. Its not something I've ever experienced, but my guess would be once you're below about 50ft youd have a chance of touching the runway.

[Guest Mark McG]

Thanks HPSOV - Wasn't sure if that became a factor or not.I have j/seated on a BA757 during CATIII ops at EGLL before 09/11.Really amazing to watch the computer land the a/c.For anyone interested in finding out more about Autoland, right click on this link to download the documennt.http://www.smartcockpit.com/b767/CAT2_3%20OPS.PDF

[Guest TheJones]

>>However am I correct in thinking that the NO LAND 3 indication>is inhibited below 200ft anyway? so the above situation>wouldn't be possible?yep, that was the catch - you got it pretty quick.The above situation I described is impossible, since NO LAND3 and AUTOLAND2 advisories are inhibited below 200ft. The reason: LAND3 take in account one spare system. If you lose one system above 200ft, you can either continue using land2 or go around. Below 200' Mrs. Boeing decided that it is not important anymore, since autoland is to be continued.Actually land3 means the level of redundancy is such "that the occurance of any single fault would not prevent the autopilot from making an automatic landing (fail operational)".Land2 means the level of redundancy is such "that any single fault does not cause a significant deviation from the flight path (fail passive)".If you get a second fault after land3 (or a first fault after land2), you will get the NO AUTOLAND light which is never inhibited.

[Guest TheJones]

EDITED for correct answer, wrong thread.Well what the heck... BUMP!

[Guest Mark McG]

bump