Alert Height

[gatbusdriver]

From the BFCTM 757

Alert heights are normally used for fail operational CAT III Ops. It is a height above the runway, above which a CAT III approach must be discontinued if a specified failure occurs.

I understand that NO LAND 3 is inhibited below alert height, NO AUTOLAND is not.

Is Alert Height 200'RA?

Cheers

Ex - gatbusdriver!!!

[qwertyuiop]

Yes. Alert height is 200' RA.

[extreme P]

In my experiences "Alert Height" is a term only associated with CAT III approaches. Typically 100' or lower RA.

http://en.wikipedia.org/wiki/Precision_approach#Low_visibility_approaches

[78deg]

On our B757 and B767 UK operator, Alert ht is 200ft RA, below this ht the ASA can only change to No Autoland, which will result in an Autopilot disconnect.

[gatbusdriver]

Thanks All

[411A]

In actual fact, alert heights can be as low as <75 feet RH, in some circumstances, especially with advanced aircraft at specific locations, using CATIIIB...Lockheed Tristar, is one example.
'Tis true.
Boeing, for many years, simply couldn't come close.

Not that anyone is surprised, I expect.:ugh:

[flyboyike]

In actual fact, alert heights can be as low as <75 feet RH, in some circumstances, especially with advanced aircraft at specific locations, using CATIIIB...Lockheed Tristar, is one example.
'Tis true.
Boeing, for many years, simply couldn't come close.

Not that anyone is surprised, I expect.:ugh:


No, absolutely no one is surprised that you made yet another post glorifying the -1011.

[Check Airman]

What can you say?

The guy loves his airplane:)

[yoyonow]

You could say that he is as out of date as his beloved airoplane.

Given that a definition of AH generally states that "if a failure affecting the fail-operational criteria occurs below the AH, it would be ignored and the approach continued (except if AUTOLAND warning is triggered)". Failure above this height would normaly lead to a go around.

Then it obviously follows that the more capable sytem is one with a higher AH....

[extreme P]

Then it obviously follows that the more capable sytem is one with a higher AH....

But we want to get down and CAT III approaches are LOW...

[gatbusdriver]

The point being (I think), with a higher alert height, you will not have to revert to LAND 2, therefore improving your chances of getting in.

[411A]

No chance of going around, gatbusdriver, with the good 'ole TriStar, it lands anyway.
Fail operational, in all respects.
Nothing finer.
Of course it is old, but then so are the pilots who fly it....now.:E

[yoyonow]

Gents, I realise that this is a rumour network but the Tech section is not realy the place for it.
411A, if the mighty Tri* is fail op in all respects then why does it have an AH. And lets not get confused with CAT III and Auto land.......
Extreme P read my post and think about it before you start SHOUTING at me, thank you.

[extreme P]

Prior to Alert Height
Immediately after recognizing the fault from the Crew Alerting System,
instrument flags, or engine indications, check autoland status annunciation.
• if the autoland status annunciation has not changed, and the equipment is
not required for the approach or can be switched, (e.g., flight director),
continue the approach
• if the autoland status annunciation has changed, or the equipment is
required for the approach, adjust to the appropriate higher minimums or
go-around.

Perhaps we are using "Alert Height" with different definitions?

Based on this bit from the BFCTM I would suggest that a lower alert height is better.

[yoyonow]

extreme P

thanks for that, have forgotten some of the Boeing speak. My point would still be (as backed up by your quote) that below alert height any failures are efectively ignored by a fail Op system and becomes fail passive. On the bus the autoland warning is the only limitation below AH.

Hence, an Eng fail above AH would require a go-around but no below. IMHO it would seem better to have a higher AH and make the "land" desicion higher rather than lower.

[767-300ER]

Yoyonow is correct...the higher the alert height the better...

I believe that the max you will find is 200'. The higher the alert height the more time there is for a failure, therefore the autoland/autopilot system has to be more capable.

Lower alert height = less capable.