SEZ GPS Runway 3 approach

C

cptndavis

New Member
Folks:
A question regarding the GPS 3 approach into Sedona, AZ...

http://flightaware.com/resources/airport/SEZ/IAP/GPS+RWY+03/pdf

MDA for this approach is 6140 MSL, which according to the chart is 1348 HAT. If I am interpreting this correctly, than the aircraft will be about 1350 feet above the ground at the MAP which is only 1.3 miles from the threshold. To me this seems like an excessively high altitude to be at so close to the runway. I realize that Sedona is located near some pretty high terrain, and I assume you want to stay high for as long as possible, but is this normal for operating in mountainous terrain? I thought I wanted to avoid high rates of descent on final approach, particularly on non-precision approaches?? I am a fairly new IFR student so I would appreciate some feedback on this

Thanks and happy flying...

Mike
 
cptndavis said:
To me this seems like an excessively high altitude to be at so close to the runway. I realize that Sedona is located near some pretty high terrain, and I assume you want to stay high for as long as possible, but is this normal for operating in mountainous terrain?
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Airports such as this often have 1) high minimums and 2) early MAP due to the protected area and climb gradients required for the missed approach. If you actually drop below MDA and then try to go missed, you might not be able to make it.

Read this:

http://www.terps.com/ifrr/may97.pdf
 
Exactly why computing a visual descent point is important!
 
cptndavis said:
MDA for this approach is 6140 MSL, which according to the chart is 1348 HAT. If I am interpreting this correctly, than the aircraft will be about 1350 feet above the ground at the MAP which is only 1.3 miles from the threshold. To me this seems like an excessively high altitude to be at so close to the runway.
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As Doug said, that's why computing (or at least guestimating) a VDP is important.

(This, BTW, is a random thought that hit me as I was reading an article on this subject, so it may not make much sense. I'm sure someone will let me know if it doesn't :) )

There are a lot of MAPs that are at the end of runway. Some, as in the case of an on-airport navaid, =after= the runway threshold.

Personally, I think there's an error in the way this stuff usually is taught. When we fly practice approaches for training purposes, traffic permitting, we usually fly to the MAP as thought MAP and MDA mean almost the same thing; as though the MAP is like a DA. We end up with the idea that the MAP is where the FAC ends.

Practically speaking, that's not really the case. The MDA is just the lowest altitude we can go without one of the runway references. That's all. And while it may be technically correct that the MAP is where the FAC ends, I think conceptually it is wrong. I think it's more helpful to think of MAP as where the missed approach procedure begins.

Where the FAC really ends is the VDP - a position where, if we see the runway, we can descend with stability and normal maneuvering.

Here's the difference: If you think of the MAP as the end of the FAC, you're still thinking about landing as you approach the MAP and you end up with the concern Mike raised - it seems awfully high. OTOH, if you think of the MAP as the beginning of the missed and use a VDP, then as you pass the VDP, you are already committed to the missed and just waiting to cross the MAP to start it. "Too high" isn't even an issue.
 
MidlifeFlyer said:
As Doug said, that's why computing (or at least guestimating) a VDP is important.

(This, BTW, is a random thought that hit me as I was reading an article on this subject, so it may not make much sense. I'm sure someone will let me know if it doesn't :) )

There are a lot of MAPs that are at the end of runway. Some, as in the case of an on-airport navaid, =after= the runway threshold.

Personally, I think there's an error in the way this stuff usually is taught. When we fly practice approaches for training purposes, traffic permitting, we usually fly to the MAP as thought MAP and MDA mean almost the same thing; as though the MAP is like a DA. We end up with the idea that the MAP is where the FAC ends.

Practically speaking, that's not really the case. The MDA is just the lowest altitude we can go without one of the runway references. That's all. And while it may be technically correct that the MAP is where the FAC ends, I think conceptually it is wrong. I think it's more helpful to think of MAP as where the missed approach procedure begins.

Where the FAC really ends is the VDP - a position where, if we see the runway, we can descend with stability and normal maneuvering.

Here's the difference: If you think of the MAP as the end of the FAC, you're still thinking about landing as you approach the MAP and you end up with the concern Mike raised - it seems awfully high. OTOH, if you think of the MAP as the beginning of the missed and use a VDP, then as you pass the VDP, you are already committed to the missed and just waiting to cross the MAP to start it. "Too high" isn't even an issue.
Click to expand...

I think that makes a lot of sense. What if we take it a step further and suggest that it might be prudent to actually begin the climb portion of the missed approach when passing the VDP with no runway in sight (while waiting to do any turns until reaching the defined MAP)? Altitude is our friend and I can't, off the top of my head, think of a situation where it is dangerous to be too high during a missed approach procedure.

One obvious variation to this theme is when we are allowed (and planning!) to circle-to-land. That is a case where the published MAP (especially when it is located at or beyond the runway threshold) can be thought of as the "last chance" to leave MDA.
 
SteveC said:
I think that makes a lot of sense. What if we take it a step further and suggest that it might be prudent to actually begin the climb portion of the missed approach when passing the VDP with no runway in sight (while waiting to do any turns until reaching the defined MAP)? Altitude is our friend and I can't, off the top of my head, think of a situation where it is dangerous to be too high during a missed approach procedure.
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Special airspace above the final approach course? Like an approach to a smaller airport below a class B where climbing early can put you in the class B while climbing after MAP would not? But I cannot think of a real world example like that.

And Midlife is 100% right, all my approaches during my IFR training were to MAP without trying to land from there, it took me flying a few in real IMC to figure out that you don't land from MAP/MDA, you go missed from there.
 
Steve, I wasn't considering the circling approach, but even when circling there is sort of a VDP issue. If you think about the protected airspace for circling, that creates sort of a "circling VDP". For example, if circling is limited to category B and A, for example, the protected airspace is only 1.5 miles from the threshhold. Tooling along at MDA, planning a circle to land, you might think in terms of 1.5 as your "circling VDP" of "circling decision point" - no runway, plan the missed when you reach the MAP.

Maybe the concept is to think in terms of predetermined "decision points" on an approach that are not ties to the MAP. VDP, itself a relatively new term, is the one that we've beguu to use formally for straight-in nonprecision approaches, is really just one application of the concept.

Just thinking out loud.
 
milski said:
Special airspace above the final approach course? Like an approach to a smaller airport below a class B where climbing early can put you in the class B while climbing after MAP would not? But I cannot think of a real world example like that.
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Lot's of 'em. All around the Memphis Class B, for example. However, a non-issue on an IFR flight plan. Controllers protect up to the missed approach altitude for an early missed and a Class B clearance isn't necessary.
 
Thanks to all for the excellent input. I have a much greater understanding of the issue now. I now see how important it is to have a VDP established.

Last question: Is VDP calculated by dividing altitude to lose by 3? This results in point to begin 3 degree glideslope descent which takes you down 300 feet per NM??

Am I correct on this??
 
if not published on the approach plate itself as a 'vdp', you can use either the dme method if available or the '10% of published' method of say, hat for example. if hat is 600' ft and the time for that approach is 4:30 Your VDP will be at 3:30 on the approach. 10% of 600' = 60 seconds, subtract that from 4:30 and you get 3:30.
 
cptndavis said:
Thanks to all for the excellent input. I have a much greater understanding of the issue now. I now see how important it is to have a VDP established.

Last question: Is VDP is calculated by dividing altitude to lose by 3? This results in point to begin 3 degree glideslope descent which takes you down 300 feet per NM??

Am I correct on this??
Click to expand...
Yep. The two most common methods for calculating a personal VDP result in a 3° glideslope:

alt to lose divided by 300 equals the VDP in nautical miles
alt to lose divided by 10 equals the VDP in seconds.
 
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