obstacle clearance on a circling approach

[bLizZuE]

I know the radii, but I can't find anywhere in the FARs or the AIM about how MUCH obstacle clearance is guaranteed for each catagory!

Help...

[surreal1221]

I should know this. . .but. . .

http://whitts.alioth.net/Pageg35%20A...20Mimimums.htm

This website says it provides 300' obstruction clearence within the radius.

Originally Posted by linked website

The MDA of a circling approach gives an obstacle clearance of 300'

No source listed.

[taseal]

look at the inst app procedures book and look at the circle to land section, it says there 300 obs clearance is provided

Edit: I'm so nice, I went down to my car, got my book and looked for ya

go to 5-7, its above the Radii figure.

I believe its 300 due to

75 feet altimeter error
100 feet pilot deviation
125 transponder pres alt error

thats worst case scenario if everything was on the negative side

correct me if I'm wrong

[B767Driver]

Yep. 300'.

[tgrayson]

Originally Posted by taseal

I believe its 300 due to

75 feet altimeter error
100 feet pilot deviation
125 transponder pres alt error

thats worst case scenario if everything was on the negative side

Unless you read that somewhere, I suspect you're trying to ascribe too much logic to an arbitrarily derived figure. The transponder figure alone is irrelevant, since it plays no role in obstacle clearance. While the 75 feet altimeter error is used in pilot literature as a gauge of altimeter system reliability, I've never seen that figure used in TERPS related documentation. And to allow only a 100 feet of pilot-induced error before the pilot hits something would be very alarming.

But, as others said, 300 feet is the correct number.

[bLizZuE]

Does it change for each category? I'm thinking no...

Thanks for your help guys. I knew it was 300, but I couldn't put my finger on a source!

[taseal]

Originally Posted by surreal1221

I should know this. . .but. . .

http://whitts.alioth.net/Pageg35%20A...20Mimimums.htm

This website says it provides 300' obstruction clearence within the radius.



No source listed.

Originally Posted by tgrayson

Unless you read that somewhere, I suspect you're trying to ascribe too much logic to an arbitrarily derived figure. The transponder figure alone is irrelevant, since it plays no role in obstacle clearance. While the 75 feet altimeter error is used in pilot literature as a gauge of altimeter system reliability, I've never seen that figure used in TERPS related documentation. And to allow only a 100 feet of pilot-induced error before the pilot hits something would be very alarming.

But, as others said, 300 feet is the correct number.

I mentioned transponder because ya know when you're low the controller goes 'low alt alert, check alt immediately etc etc'

I kinda just made that up as to why it might be 300, thats why I said 300, so maybe right, maybe wrong heh...

[tgrayson]

I kinda just made that up as to why it might be 300

So I figured. However, you probably convinced some readers, since your numbers added up.

[taseal]

Originally Posted by tgrayson

So I figured. However, you probably convinced some readers, since your numbers added up.

maybe it is 300 because of that?

now i'm actually curious haha

[tgrayson]

Originally Posted by bLizZuE

Does it change for each category? I'm thinking no...

Thanks for your help guys. I knew it was 300, but I couldn't put my finger on a source!

Hmmmmm...You didn't read the articles I gave you.


http://www.terps.com/ifrr/jan96.pdf

[bLizZuE]

Originally Posted by tgrayson

Hmmmmm...You didn't read the articles I gave you.


http://www.terps.com/ifrr/jan96.pdf

I have to be honest, I thought to myself when I was first posed the questions..."I wonder if they're in those .pdfs I have..."

I thought...NAAAA



lol

[Hacker15e]

Originally Posted by taseal

I mentioned transponder because ya know when you're low the controller goes 'low alt alert, check alt immediately etc etc'

I've never had a controller say this when I'm inside the FAF or have all ready commenced the circle.

Is that normal?? Are they even watching your mode C hit when you're circling??

[surreal1221]

Originally Posted by Hacker15e

I've never had a controller say this when I'm inside the FAF or have all ready commenced the circle.

Is that normal?? Are they even watching your mode C hit when you're circling??

No, because you're on a segment of an already established approach.

Low altitude alerts will occur (traditionally) in areas where an MVA is being penetrated by a pilot that failed to maintain his/her latest altitude assignment that was say AT the MVA, or slightly above it.

[averyrm]

The system for low altitude alerts (in the NE at least) predicts your descent rate and if it sees you'll hit the specified altitude (mda) before a fix (map), say on a localizer approach, it'll ring the bell.

I got one every single time I shot the LDA into Hartford, CT.

[tgrayson]

Originally Posted by surreal1221

No, because you're on a segment of an already established approach.

You can still get them in this situation. I've heard our local tower relay a warning to an aircraft on a circling approach. I have the impression that each facility can program its MSAW as it desires.

The 7110.65 contains language warning a pilot of what MDA/DH is, so it's obviously not limited to MVA. You can also get them with a high rate of descent on a non-precision approach (The MSAW software looks at your trend and freaks.)

[surreal1221]

touche. . .

But I wouldn't consider it a normal thing.

[taseal]

Originally Posted by surreal1221

No, because you're on a segment of an already established approach.

Low altitude alerts will occur (traditionally) in areas where an MVA is being penetrated by a pilot that failed to maintain his/her latest altitude assignment that was say AT the MVA, or slightly above it.

i was told this while shooting a LOC into FXE, we were about 500 agl i'd say...