Decision Height - one for Clanad perhaps?!!

[brachiopod]

Just been reading the AAIB report into the 'crash' landing of the TNT 737 Cargo plane at Birmingham airport in 2006. Not knowing what a "CAT III a" landing was, I looked it up. But what is meant by 'decision heights' referred to in the various ILS landing categories?

[wee willie]

clanad may be (Six O'Clock- Tea-time) lol

[kempie]

Shw mae brachi

I have spotted Clanad on the Recent posts list but if he doesn't spot this thread I shall interject with this:

http://en.wikipedia.org/wiki/Instrument_approa ch#Decision_Height_or_Altitude

[Clanad]

Glad to be of assistance, brachiopod (still classifying fossils is Scotland?)

The Instrument Landing System (ILS) that electronically guides an appropriately equipped aircraft to a specific runway during inclement weather consists of several components, but to simplify the discussion, one needs to only consider the lateral (left and right) guidance called the localizer and the vertical guidance called the glide slope. The aircrat instruments presents this information in the form of a "cross hair" device (for the pedantic, yes I know the flight director is involved.)
In the Category III (actually there's IIIA, IIIb and IIIC as well as Cat I and Cat II), each with succedingly lower allowances for descent. The highest CAT I, has a Decision Height (DH = height above ground level at the runway threshold, usually) of 200 feet, down to essentially zero for CAT IIIC. Technically speaking, CAT IIIC has no DH since it's an autoland procedure, utiliizing an approved auto pilot. CAT IIIA allows descent to 100 feet at which time the pilot must have the runway environment in sight (let me tell you from experience, it happens really, really fast at about 130 knots airspeed or so). CAT III B allows DH of 50 feet...
If the runway environment isn't in sight a "missed approach" must be executed. It isn't uncommon for the main gear wheels to actually touch down during the missed approach procedure from CAT III of any class.
Most airports are not equipped for CAT III landings other than the major airports. Most are CAT I or at best CAT II...
These all are precision approaches but there are still non-precision approaches in use that use Minimum Descent Altitude (MDA) as the descent limits. These are usually around 500 feet or so and also require a minimum reported visibility, usually 1/2 mile... More thanyou ever wanted to know, I'm sure
Thanks for asking!

[brachiopod]

Hi all! And thanks for your replies (Diolch, kempie !).

Well, Clanad, now I have two nektonic 'pod larvae - I just don't have much time for anything these days!

So, are we saying that all ILS landings ultimately rely on a visual reference at some point prior to touchdown or else it's a go-around?

[Clanad]

Yes, with the exception of CAT IIIC, which is conducted entirely with the auto--land authorized autopilot. The aircraft si required to be equipped with selectable auto-brakes as well. All others require visual identification of the runway... by the way, here's a pretty good depiction of a Boeing 737-800 CATIIIBlanding, however the weather conditions appear to be well above 50 feet...

https://www.youtube.com/watch?v=M3wnl1Ut--o

The state of the art is rapidly changing, however with the advent of GPS and syntheticl vision technology...

By the way, brachiopod I hope to go back to Hell Creek this summer for an excavation of an Orectolobid shark (Brachaelurus estesi). There's a plethora of bivalves... Granocardium, Hiatella, Leptosolen. et al... common as sagebrush in the formation... I'll be thinking of you in cool England when it's 100 degrees F in the outback of Montana...

[brachiopod]

I think the link illustrates it pretty well !

As for the dig, the closest I'm going to get is building the kids' sandcastles on the beach! Fancy swapping Hell Creek for a wet week in Wales?

[Clanad]

Hmmm... let me think about that one... it does have it's charm, though... good talking to you again!

[brachiopod]

Likewise ! Catch up soon.


pod.

[wee willie]

what the heck doe's pod mean?

[figure]

Clanad, you must have a very, very interesting and exciting career. Love to read your posts - always something to learn from them.

[Clanad]

Any of various marine invertebrate animals of the phylum Brachiopoda that resemble clams. Brachiopods have paired upper and lower shells attached to a usually stationary stalk and hollow tentacles covered with cilia that sweep food particles into the mouth. Brachiopods are probably related to the phoronids and bryozoans, and were extremely abundant throughout the Paleozoic Era. Shortened to pod by the host of this thread...

[Clanad]

Why, thanks, figure although in most cases it was being in the right place at the right time... you're much kinder than Mrs. C who simply states that I'm a walking compendium of absolutely useless facts...But, she makes great sourdough pancakes from starter that's at least 50 years old... so I'll keep her around...

[Panic Button]

That TNT 737 sat at Birmingham on supports for months, probably while insurance companies argued.

Then I saw it being broken up and carted away.

I expect all the servicible bits were removed for re-use. as there is a considerable market for that.

[Toureman]

I liked your utube video, good job the passengers don't have access to a front view when landing under a Cat 3.