Note to self, don't follow approach plates.

[roncachamp]

The VDP feature of this type of approach assures the pilot that a 34:1 slope from the VDP to the runway threshold is free of obstructions.”

I'm going by this statement and the fact the pilot didn't say anything about the approach not having shading. Like I said I don't have a pre 2008 approach plate so I don't know if it had shading or even if it was used back then.

That's the statement of the insurance company covering the incident aircraft, but what was their source? This shaded area is described in the AIM today, but was it there in 2008? I don't have an AIM from 2008 but I do have one from 2006, this paragraph is part of the description of Vertical Descent Angles on Nonprecision Approaches:

Pilots should be aware that the published angle

is for information only − it is strictly advisory
in nature. There is no implicit additional obstacle
protection below the MDA. Pilots must still
respect the published minimum descent altitude
(MDA) unless the visual cues stated 14 CFR​

Section 91.175 are present. In rare cases, the pub-
lished procedure descent angle will not coincide
with the Visual Glide Slope Indicator (VGSI);
VASI or PAPI. In these cases, the procedure will
be annotated: "VGSI and descent angle not coin-
cident."

The thing is if the VASI was bringing people into the trees I would think the VDP was coinciding with the VASI. Also you have an FAA inspector saying the approach should have had a 47 ft TCH 500 ft down the runway. Based on that statement and the fact the approach was changed, it sure seems like the VDP was in the wrong spot. Either that, or trees grew into the OCL after initial cert.

The initial cert was good, I spoke with the flight check pilot that did it. The trees did grow into the slope later, that's why the VASI was shut down. The plate had erroneous information, but it appears the errors were all in the information that the AIM says is "strictly advisory in nature."

 

[roncachamp]

Well that clears it up. Apparently it used to be obstruction free. I'd say they had a VDP and a VASI that used to work fine until the trees grew. They solved the problem by shuting down the VASI and removing the shaded area. The expensive way would be to displace the threshold, but with houses on the departure end of 5, I'm not sure if that would be doable. Still, without a VASI and a VDP that keeps you clear of obstacles, going in there at night would be a little dicey. I guess you just make sure nothing blocks your view of the runway end identifier lights and land long!

The VASI was shut down in April 2006 because of the tree growth, but the NOTAM probably just said it was out of service without stating the reason. Providing the reason would probably have been helpful; if the VASI is obstructed so is the coincident VDA. A NOTAM stating the VDA was obstructed by trees would probably have been helpful too.

 

[azure]

The VASI was shut down in April 2006 because of the tree growth, but the NOTAM probably just said it was out of service without stating the reason. Providing the reason would probably have been helpful; if the VASI is obstructed so is the coincident VDA. A NOTAM stating the VDA was obstructed by trees would probably have been helpful too.

Then why did the plate from Dec 2007 have the 34:1 clear symbol?

 

[roncachamp]

Then why did the plate from Dec 2007 have the 34:1 clear symbol?

Because it hadn't been removed. From the article attached to the OP:

Two years earlier, in April 2006, one email stated: “FAA flyover inspection shutdown VASI on Runway 05. Flight Inspection Report states, ‘Obstacle clearance unsatisfactory due to trees near threshold.’”

Shutting down a VASI warrants a NOTAM. The article does not state what NOTAMS were in effect at the time of the incident.

 

[Velocity173]

That's the statement of the insurance company covering the incident aircraft, but what was their source? This shaded area is described in the AIM today, but was it there in 2008? I don't have an AIM from 2008 but I do have one from 2006, this paragraph is part of the description of Vertical Descent Angles on Nonprecision Approaches:





The initial cert was good, I spoke with the flight check pilot that did it. The trees did grow into the slope later, that's why the VASI was shut down. The plate had erroneous information, but it appears the errors were all in the information that the AIM says is "strictly advisory in nature."

Yes, their source was the DEC 2007 approach plate. It had shading. Yes we all know it's advisory in nature but if this pilot has an approach plate that shows the 34:1 OCS is suppose to be clear and it's not, well he has a case.

 

[azure]

Because it hadn't been removed.

Ummm... what I was getting at is, why hadn't it been removed? Or is that symbol, like the VDP, only considered "advisory"? I thought it meant a 34:1 slope down to the threshold was assured to be clear?

 

[roncachamp]

Yes, their source was the DEC 2007 approach plate.

Given that it doesn't appear in any other publication directed to pilots that does appear to be the likely source.

It had shading. Yes we all know it's advisory in nature but if this pilot has an approach plate that shows the 34:1 OCS is suppose to be clear and it's not, well he has a case.

I have a problem with the language in the TPP legend and that in the AIM about VDAs. If the published angle is for information only, if it is strictly advisory in nature, if there is no implicit additional obstacle protection below the MDA, as it says in the AIM, then why does the TPP legend say "Visual segment below MDA/DA is clear of obstacles on 34:1 slope" when the shaded area is present?

 

[azure]

I have a problem with the language in the TPP legend and that in the AIM about VDAs. If the published angle is for information only, if it is strictly advisory in nature, if there is no implicit additional obstacle protection below the MDA, as it says in the AIM, then why does the TPP legend say "Visual segment below MDA/DA is clear of obstacles on 34:1 slope" when the shaded area is present?

AIM 5-4-5h.1 says that the published angle provides no implicit obstacle protection below the MDA, but then 5-4-5h.2 goes on to say that:

Additional protection for the visual segment below the MDA is provided if a VDP is published and descent below the MDA is started at or after the VDP.

The mention of the shaded arrowhead indicating that the 34:1 visual surface is clear is in that same paragraph, so to me that says that it implies that additional protection actually is supposed to be present and the symbol is more than advisory. But maybe that's not the way it's intended to be read.

My other question about all of this is about the semantics of the term "34:1 surface". Where is that surface measured from? Is that surface anchored at the point where the descent is allowed to begin (in this case, the VDP), or at the runway threshold at TCH? If the first is correct, then that is a much shallower slope than the one leading from the VDP at MDA to the threshold at TCH and could very well have been clear. I always assumed it was the second, though.

 

[roncachamp]

Ummm... what I was getting at is, why hadn't it been removed?

You don't amend plates for things that may be temporary in nature, you issue a NOTAM. I'd like to know what NOTAMs were in effect at the time of this incident.

Or is that symbol, like the VDP, only considered "advisory"? I thought it meant a 34:1 slope down to the threshold was assured to be clear?

The AIM says strictly advisory in nature, the TPP says clear of obstacles. One of 'em is fibbin'.

 

[roncachamp]

AIM 5-4-5h.1 says that the published angle provides no implicit obstacle protection below the MDA, but then 5-4-5h.2 goes on to say that:

"Additional protection for the visual segment below the MDA is provided if a VDP is published and descent below the MDA is started at or after the VDP."

The AIM didn't go on to say that in 2006, I don't know if it said it in 2008.

 

[Velocity173]

AIM 5-4-5h.1 says that the published angle provides no implicit obstacle protection below the MDA, but then 5-4-5h.2 goes on to say that:

The mention of the shaded arrowhead indicating that the 34:1 visual surface is clear is in that same paragraph, so to me that says that it implies that additional protection actually is supposed to be present and the symbol is more than advisory. But maybe that's not the way it's intended to be read.

My other question about all of this is about the semantics of the term "34:1 surface". Where is that surface measured from? Is that surface anchored at the point where the descent is allowed to begin (in this case, the VDP), or at the runway threshold at TCH? If the first is correct, then that is a much shallower slope than the one leading from the VDP at MDA to the threshold at TCH and could very well have been clear. I always assumed it was the second, though.

You can look up FAA manual 8260.3B Par 251A (1) (C) and see how they go about doing it. The surface area they use for the obstructions is 200 ft from the approach end at THR height. They either use 20:1 for circling or 34:1 for straight OCS. Of course they also use the 34:1 to obtain the VDP. I had a TERPs class in the Instrument Examiner course but they didn't cover VDPs so I'm no expert on how they configure them. Calculating an Emergency Copter GPS Approach I can do. :wink2:

 

[azure]

You can look up FAA manual 8260.3B Par 251A (1) (C) and see how they go about doing it. The surface area they use for the obstructions is 200 ft from the approach end at THR height. They either use 20:1 for circling or 34:1 for straight OCS. Of course they also use the 34:1 to obtain the VDP. I had a TERPs class in the Instrument Examiner course but they didn't cover VDPs so I'm no expert on how they configure them. Calculating an Emergency Copter GPS Approach I can do. :wink2:

Thanks, but I can't seem to find a version of that manual that even has a paragraph 251A (or 251). I downloaded the version with changes 1-25 from the FAA website. It doesn't have a 251A and 251 is still Reserved. Is there a more recent version?

BTW it's been over a week since I checked, but I'm pretty sure that in this case, the VDP is well above the 34:1 surface from the threshold and closer to the 3 degree published VDA.

 

[denverpilot]

I find it kinda interesting that there didn't used to be VDPs and they were touted as "safer" approches to add them...

And of course, like other complex systems I've administered over the years, the added responsibility of handling and correcting MORE data, never truly works out the way intended in the end.

They have more work to do to keep on top of all the VDP data now. More work, smaller budget, smaller staff... think critically about how that's bound to turn out for at least some number of approaches...

Where things like trees are growing and getting taller... and taller... and taller...



(May not be 100% related to this particular case, but there's always this impression that adding MORE DATA, MORE DATA, will fix things in complex systems, and it rarely really does...)

 

[Velocity173]

Thanks, but I can't seem to find a version of that manual that even has a paragraph 251A (or 251). I downloaded the version with changes 1-25 from the FAA website. It doesn't have a 251A and 251 is still Reserved. Is there a more recent version?

BTW it's been over a week since I checked, but I'm pretty sure that in this case, the VDP is well above the 34:1 surface from the threshold and closer to the 3 degree published VDA.

You should be able to find an 8260.3 B CHG 19 online. Not sure if CHG 19 is the newest version, it's just the copy I have.

I should've worded the 34:1 VDP differently. They don't use that to get the VDP, it's used for the OCS. VDPs are mostly 3 degrees so that would be a steeper 19:1 ratio over the 34:1 OCS.

 

[roncachamp]

Thanks, but I can't seem to find a version of that manual that even has a paragraph 251A (or 251). I downloaded the version with changes 1-25 from the FAA website. It doesn't have a 251A and 251 is still Reserved.

And yet "251. Visual Portion of the Final Approach" appears in the Table of Contents. Go figure.

Is there a more recent version?

That appears to be the most recent.