TDZE

[c172captain]

Sorry if this is random, but I have it stuck in my head and need it clarified...

TDZE-Touchdown Zone Elevation... just for clarification, does it stand for "the elevation you can descend down to if the approach lights of the runway used for intended landing come into sight once reaching your Decision Altitude (DA) on an Instrument Approach"

That was put into my own words so that I could understand it ; how accurate is that definition?

 

[derg]

Basically the elevation, in MSL, of the touchdown zone of the runway.

 

[c172captain]

Basically the elevation, in MSL, of the touchdown zone of the runway.

Is there a specific elevation that you're allowed to descend down to once you have the approach lights in sight? I remember my Checkride Instructor chewing me out because I couldn't name the specific term, I just kept saying that you descend 100ft :whatever: Maybe I'm getting my scenarios wrong too... can't say I remember all too clearly

 

[derg]

You know, I can't give you the textbook answer so hopefully someone with the textbook answer can chime in!

But yes, you're getting warmer!

 

[Maurus]

(c) Operation below DH or MDA. Where a DH or MDA is
applicable, no pilot may operate an aircraft, except a military
aircraft of the United States, at any airport below the authorized
MDA or continue an approach below the authorized DH unless —
(1) The aircraft is continuously in a position from which a
descent to a landing on the intended runway can be made at a
normal rate of descent using normal maneuvers, and for
operations conducted under Part 121 or Part 135 unless that
descent rate will allow touchdown to occur within the
touchdown zone of the runway of intended landing.
(2) The flight visibility is not less than the visibility prescribed in
the standard instrument approach procedure being used; and
(3) Except for a Category II or Category III approach where any
necessary visual reference requirements are specified by the
Administrator, at least one of the following visual references
for the intended runway is distinctly visible and identifiable
to the pilot:
(i) The approach light system, except that the pilot
may not descend below 100 feet above the touchdown
zone elevation using the approach lights as a
reference unless the red terminating bars or the red
side row bars are also distinctly visible and
identifiable.
(ii) The threshold.
(iii) The threshold markings.
(iv) The threshold lights.
(v) The runway end identifier lights.
(vi) The visual approach slope indicator.
(vii) The touchdown zone or touchdown zone markings.
(viii) The touchdown zone lights.
(ix) The runway or runway markings.
(x) The runway lights.

There is your textbook answer. You may descend to 100 feet above the TDZE if you have the approach lighting system but not the red terminating bars or the red
side row bars in sight.

Notice how it isn't worded to descend 100 ft as a Cat 1 ILS can have a DA higher than 200 feet. So if the DA is 250 feet you can descend 150 feet if you have the approach lighting system but not the red terminating bars.


Also for a definition for TDZE:

Touchdown Zone Elevation (TDZE) – The highest
elevation in the first 3,000 feet of the landing surface.

 

[jake.durham]

If you only have the approach lights in sight you may continue the approach through the DH to a height of 100 feet above the TDZ at which point you must have the remaining elemtents (terminating lights, reils, runway, etc...) to make a normal landing.

Hope this helps.

 

[ajf005]

Is there a specific elevation that you're allowed to descend down to once you have the approach lights in sight? I remember my Checkride Instructor chewing me out because I couldn't name the specific term, I just kept saying that you descend 100ft :whatever: Maybe I'm getting my scenarios wrong too... can't say I remember all too clearly

He was probably chewing you out because if you think you can only descend 100 feet below MDA/DH then you may sell yourself short on say at GPS approach where you're what 500 AGL at MDA? (its been a while since Ive shot one) Then you only go down to 400 AGL with the approach lights in sight instead of down to 100 AGL and have to go missed. Of course this is all hypothetical...ive never not seen the runway once I've gotten the approach lights but it can happen.

 

[surreal1221]

Take a look at 91.175. . .

edit: nevermind, someone already gave you the fish instead of teaching you to fish.

 

[Maurus]

Take a look at 91.175. . .

edit: nevermind, someone already gave you the fish instead of teaching you to fish.

Yes because giving the exact location of the reg is that much better.:crazy:

 

[Clocks]

Damn I was recording an audio file of me reading the reg...

Thanks for ruining it Maurus!

 

[Maurus]

Well you could always shoot an ILS to mins following the reg and post it on Youtube.:nana2:

 

[surreal1221]

Hey, do it on FS98!!1

 

[bdhill1979]

Also for a definition for TDZE: Quote:Originally Posted by Instrument Procedures Handbook
Touchdown Zone Elevation (TDZE) – The highest
elevation in the first 3,000 feet of the landing surface.

Also if a runway is less than 6000 feet long the touchdown zone is the first half of the usable runway.


As was mentioned before the main thing to remember about descending below DA is not that it is just another 100 feet, that assumes that DA is always 200 above TDZE, it isn't always. I have students trying to screw that up constantly even though I spent 20 minutes repeating to them "100 above TDZE, not just another 100 feet....say it with me now....."