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Old June 3rd, 2012, 05:11 PM   #1
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TDZE changed to THRE

Hi folks,

I'm an instrument student ready for my check ride, and couldn't get a good answer to this question today.

I noticed with the latest approach plates that in addition to a slew of changes to the RNAV 17 at JYO, the TDZE has now become THRE, which is 5 feet lower. LPV minimums are still 250' AGL so as a result the MSL minimum is 5 feet lower. Same for the ILS. Flipping through the book I noticed a lot of airports now have THRE instead of TDZE. I get that the new number is just measured at the threshold instead of the TD zone, but I'm trying to understand why they'd change it. Is this an ongoing change the FAA is now making? Will I be able to go down to 100' above THRE if I have approach lights in sight, or is that option now gone?

Thanks
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Old June 3rd, 2012, 05:55 PM
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Re: TDZE changed to THRE

From what I have gathered it is an ICAO thing. ICAO measures from the threshold and not touchdown. So the FAA is just replacing the numbers with the "correct" ICAO measurement system. I haven't found anything about if the 100' above TDZE is gone or not. I would think you can still descend down to 100' above THRE. I think its a gray area right now. 91.175 (3)(c)(i) still states 100' above TDZE.

Here is the TERPS change eff 12/07/07 FAA wants to "harmonize" with European standards.

http://fsims.faa.gov/wdocs/orders/8260_3b-ch20.htm
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Old June 3rd, 2012, 06:33 PM
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Re: TDZE changed to THRE

It also appears that straight-in DH/MDA is referenced to Height above Threshold (HAT). I found this on page 8-27 of my Instrument Flying Handbook. You would think that since 91.175 (c) states:

(c) Operation below DA/ DH or MDA. Except as provided in paragraph (l) of this section, where a DA/DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, below the authorized MDA or continue an approach below the authorized DA/DH unless—

that you can still descend below DH/MDA.

However I just got of the phone with my CFI-I and he said it sounds like a huge gray area. So I don't have a clear cut answer on that question. If it was me I would try to get a hold of your local FSDO and ask them for there view.

Addition: I will be calling my local FSDO tomorrow. I just saw that the charting office also just added THRE to our local plates.
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Old June 3rd, 2012, 06:52 PM
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Re: TDZE changed to THRE

Quote:
Originally Posted by dukeblue219 View Post
Hi folks,

I'm an instrument student ready for my check ride, and couldn't get a good answer to this question today.

I noticed with the latest approach plates that in addition to a slew of changes to the RNAV 17 at JYO, the TDZE has now become THRE, which is 5 feet lower. LPV minimums are still 250' AGL so as a result the MSL minimum is 5 feet lower. Same for the ILS. Flipping through the book I noticed a lot of airports now have THRE instead of TDZE. I get that the new number is just measured at the threshold instead of the TD zone, but I'm trying to understand why they'd change it. Is this an ongoing change the FAA is now making? Will I be able to go down to 100' above THRE if I have approach lights in sight, or is that option now gone?

Thanks
The TERPs term is HATh for Height Above Threshold. Like another poster stated, it is a change to harmonize with the ICAO way of doing things.

Of course, 91.175 should now read "above TDZ or HATh as appropriate." But, it doesn't.

If your FSDO has the definitive answer ask for it in writing.
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Old June 3rd, 2012, 08:26 PM
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This "Europization" of U.S. Aviation is stupid. Only big iron pilots had to remember the differences before, and they have specialized training and coursework plus time in two-pilot crews to sort it all out.

It's not adding to safety or helping anyone else one iota here who has 20-30 years of the U.S. systems memorized and understood.

There's no logical argument FAA can make (because "standardization" isn't a logical argument) for safety on this stuff. Airline and corporate crews already had ways to teach this stuff. The rest of us are just confused by it all. Confusion isn't adding to safety, it's a detractor.
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Old June 3rd, 2012, 09:03 PM   #6
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Re: TDZE changed to THRE

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Originally Posted by denverpilot View Post
This "Europization" of U.S. Aviation is stupid. Only big iron pilots had to remember the differences before, and they have specialized training and coursework plus time in two-pilot crews to sort it all out.

It's not adding to safety or helping anyone else one iota here who has 20-30 years of the U.S. systems memorized and understood.

There's no logical argument FAA can make (because "standardization" isn't a logical argument) for safety on this stuff. Airline and corporate crews already had ways to teach this stuff. The rest of us are just confused by it all. Confusion isn't adding to safety, it's a detractor.
Submitting to ICAO is the way of the U.S. Government. Keep in mind the FAA is a small fifdom under a very insiginificant cabinet member.

I remember how p***d I was when they went from sequence reports to that ICAO cr*p.

Getting older, I recently had two hospital stays where all the equipment was in metrics. None of the nurses could read metric.

On the flip side, the Ruskies used meters for eons for altitude. They recently changed to feet. If meters (excuse me, metres) are so great why doesn't all of ICAO use meters for altitude and airspeed?

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Old June 3rd, 2012, 09:24 PM
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Quote:
Originally Posted by aterpster View Post
Submitting to ICAO is the way of the U.S. Government. Keep in mind the FAA is a small fifdom under a very insiginificant cabinet member.
That seems to insinuate that there were "orders from above" to FAA to submit. I've seen no evidence of that.

I see a bunch of people changing things for the sake of change without thinking about it, more than I see directives to behave like Europe.

Did Congress or a definable Administration appointee say FAA needed to do it? I can't find that document anywhere.

I also can't imagine my particular elected officials defending it or requesting it in Washington.

I'm going with "stupid is as stupid does" unless there's evidence to the contrary in this particular case. Who's pushing for it, and why?
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Old June 4th, 2012, 02:47 AM   #8
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Re: TDZE changed to THRE

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Originally Posted by denverpilot View Post
That seems to insinuate that there were "orders from above" to FAA to submit. I've seen no evidence of that.
This harmonization effort for approach minimums has been underway for probably 15 years, or so. I believe the State Department is the department of protocol for the U.S.

That may be implicit rather than explicit. I do know the FAA receives formal written invitation froms ICAO headquarters on a regular basis. That is the practical working-level basis.

When the FAA desires to non-concur with an ICAO specification, such as MVA charts for pilots, they must file a formal exception through the State Dept.
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Old June 4th, 2012, 10:33 AM
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Re: TDZE changed to THRE

Quote:
Here is the TERPS change eff 12/07/07 FAA wants to "harmonize" with European standards.
ICAO isn't a "European" standard. It's an international standard.

Quote:
On the flip side, the Ruskies used meters for eons for altitude. They recently changed to feet. If meters (excuse me, metres) are so great why doesn't all of ICAO use meters for altitude and airspeed?
The Russians still issue meters, but not for everything. Russian ATC also (in some places) issues meters down to lower altitudes in the terminal area, then issues in feet once below the transition level. They also still use QFE, rather than QNH for altimeter, but will usually issue QNH if specifically requested.
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Old June 4th, 2012, 10:53 AM
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Re: TDZE changed to THRE

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Originally Posted by DouglasBader View Post
The Russians still issue meters, but not for everything. Russian ATC also (in some places) issues meters down to lower altitudes in the terminal area, then issues in feet once below the transition level. They also still use QFE, rather than QNH for altimeter, but will usually issue QNH if specifically requested.
Well, actually, Russia just converted to feet, at least in the flight levels, a couple of months, or so, ago. Not sure what they do below the transition level. I will have to remember to look next time I go to work.
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Old June 4th, 2012, 11:22 AM
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Re: TDZE changed to THRE

We can only hope that the FAA doesn't decide to "harmonize" the medical standards with Europe....
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Old June 4th, 2012, 12:15 PM   #12
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Re: TDZE changed to THRE

Quote:
Originally Posted by denverpilot View Post
This "Europization" of U.S. Aviation is stupid. Only big iron pilots had to remember the differences before, and they have specialized training and coursework plus time in two-pilot crews to sort it all out.

It's not adding to safety or helping anyone else one iota here who has 20-30 years of the U.S. systems memorized and understood.

There's no logical argument FAA can make (because "standardization" isn't a logical argument) for safety on this stuff. Airline and corporate crews already had ways to teach this stuff. The rest of us are just confused by it all. Confusion isn't adding to safety, it's a detractor.
The 'I' in ICAO stands for 'International' ie one world standard as we should have, quit your bitching, the language could have been French and then you'd have to learn another language to fly out of the country.
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Old June 4th, 2012, 12:44 PM
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Re: TDZE changed to THRE

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Originally Posted by Henning View Post
The 'I' in ICAO stands for 'International' ie one world standard as we should have, quit your bitching, the language could have been French and then you'd have to learn another language to fly out of the country.
To take that to completion the FAA should not be allowed to file exceptions, in which case we would have MVA charts in our manual like we do for many other countries. There wouldn't be TERPs criteria, either.
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Old June 4th, 2012, 01:14 PM
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Old June 4th, 2012, 03:12 PM
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Re: TDZE changed to THRE

I still have not found the answer to your question. I have called AeroNav, AOPA and our local FSDO. Both AOPA and the FSDO referred me back to AeroNav which makes sense. Go to the source to get the information.

AeroNav said they will get back to me in a few days with their answer.
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Old June 5th, 2012, 03:01 PM
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Re: TDZE changed to THRE

Quote:
Originally Posted by ARFlyer View Post
I still have not found the answer to your question. I have called AeroNav, AOPA and our local FSDO. Both AOPA and the FSDO referred me back to AeroNav which makes sense. Go to the source to get the information.

AeroNav said they will get back to me in a few days with their answer.
Hmm, thanks for checking into it. Much appreciated...
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Old June 6th, 2012, 10:06 AM   #17
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Re: TDZE changed to THRE

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Originally Posted by denverpilot View Post
Did Congress or a definable Administration appointee say FAA needed to do it? I can't find that document anywhere.

I also can't imagine my particular elected officials defending it or requesting it in Washington.

I'm going with "stupid is as stupid does" unless there's evidence to the contrary in this particular case. Who's pushing for it, and why?
People in the government who need to justify their jobs. If they're not being kept busy with the ever-underfunded NextGen mandate, they'd better find something else to do, lest they get cut. Where do you think all the TSA nonsense comes from?
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Old June 12th, 2012, 01:56 PM
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Re: TDZE changed to THRE

Quote:
Originally Posted by ARFlyer View Post
I still have not found the answer to your question. I have called AeroNav, AOPA and our local FSDO. Both AOPA and the FSDO referred me back to AeroNav which makes sense. Go to the source to get the information.

AeroNav said they will get back to me in a few days with their answer.
Anything yet?
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Old June 19th, 2012, 06:19 PM
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Re: TDZE changed to THRE

Oops did not see your reply. Well AeroNav basically said

Andrew,

THRE is threshold elevation and TDZE is touchdown zone elevation - which is the highest elevation in the first 3000 feet.

This is a criteria change that we are now using threshold elevation in determining the HAT versus touchdown zone elevation. This change is not related to the 91.175.

Thanks,
AeroNav


Our local FSDO said that they think its interchangeable, but it is in no way an official statement from the FSDO or the FAA. The FSDO said the FAA has never come out with any statements or memos about the change. So it was a one pilot to another type answer.

Does that answer your question?
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Old June 20th, 2012, 01:57 AM
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