Procedure Turn Profile View

Areeda

Pattern Altitude
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Aug 21, 2005
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Areeda
After the excellent thread Ron started on the 1D2 VOR-A procedure turn altitudes, I decided to look at a lot of profile views. For those interested this meant fixing my database of NACO plates, it is on-line again at poa.areeda.com.

Here's a summary. I'm looking for more. I realize I could use more resolution in the images but they are readable as is. I did it as an html page to make it easier to edit than a post.

Most of them I understand, please don't make fun of my questions.

There are two examples KBIH VOR/GPS-A and KERY VOR/GPS RWY11 where an intersection is defined on a descent with no altitudes, turns or other discernible actions and no indication how to identify them with minimum equipment, at least by me. Are these there for situational awareness? If so what do they offer beyond DME distance.

On the KDLO VOR-RWY32 there is a non-precision descent angle of 2.94° to the VDP, does this a suggested, min or maximum angle?

Joe
 
The VDP is defined by the intersection of the the stated glide angle up from the touchdown zone with the MDA. Normally it's 3.00 degrees, but may vary for reasons that are no doubt buried somewhere in TERPS. What it's telling you is that if you descend from MDA prior to the VDP, you may be using less than a "normal rate of descent" and in an extreme case, may not clear all obstacles; if you start down after that, you may have to use more than a "normal rate of descent" to reach the runway touchdown zone. See 91.175(c)(a) for the implications of leaving MDA from a position requiring more or less than a "normal rate of descent."

BTW, the angle you see on the profile view is the angle your WAAS GPS will use on a GPS approach with vertical guidance.

And to expand on Scott's discussion of the phantom waypoints (and they are GPS waypoints, not VOR intersections), the GPS needs two points to define a straight line such as the final approach course. When the navaid is on the field, there is no other point on the approach to use to define the final approach course line, so they throw in a phantom waypoint that is computed to be on the final approach course. That way, your GPS can draw the line from the airport out the final approach course to provide guidance through the entire approach without going into OBS mode.
 
BTW, the angle you see on the profile view is the angle your WAAS GPS will use on a GPS approach with vertical guidance.

Ron,
I agree that the angle is what a WAAS GPS would use, however you would not see that angle symbol on a GPS approach with LPV minimums. The angle (for LPV) would be indicated with e.g. "GS2.97[FONT=&quot]º[/FONT]" shown above the TCH. The Vertical Descent Angle (VDA) angle symbol (right angle symbol)(sorry, don't know how to show it here), is actually provided for people who have no vertical navigation information. As the AIM explains, it is used along with groundspeed and a "rate of descent table" to estimate a rate of descent that will help to provide a stabilized descent.

AIM 5-4-5 i.3.Pilots may use the published angle and estimated/actual groundspeed to find a target rate of descent from the rate of descent table published in the back of the U.S. Terminal Procedures Publication. This rate of descent can be flown with the Vertical Velocity Indicator (VVI) in order to use the VDA as an aid to flying a stabilized descent. No special equipment is required.

WAAS GPS uses the same method as used for the VDA to determine the angle, but I guess my point is that the angle shown really is not the GPS angle, but an angle for use if you have no other means to establish a stabilized descent. The answer is the same, but a slightly different purpose and different symbology.

gary

 
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The VDP is defined by the intersection of the the stated glide angle up from the touchdown zone with the MDA. Normally it's 3.00 degrees, but may vary for reasons that are no doubt buried somewhere in TERPS. What it's telling you is that if you descend from MDA prior to the VDP, you may be using less than a "normal rate of descent" and in an extreme case, may not clear all obstacles; if you start down after that, you may have to use more than a "normal rate of descent" to reach the runway touchdown zone. See 91.175(c)(a) for the implications of leaving MDA from a position requiring more or less than a "normal rate of descent."

BTW, the angle you see on the profile view is the angle your WAAS GPS will use on a GPS approach with vertical guidance.

And to expand on Scott's discussion of the phantom waypoints (and they are GPS waypoints, not VOR intersections), the GPS needs two points to define a straight line such as the final approach course. When the navaid is on the field, there is no other point on the approach to use to define the final approach course line, so they throw in a phantom waypoint that is computed to be on the final approach course. That way, your GPS can draw the line from the airport out the final approach course to provide guidance through the entire approach without going into OBS mode.

I'm curious why two fixes are required to create a course leg given that (with TSO C146a navigators) one of the 23 supported leg types is "course to a fix". Course to fix only requires one waypoint plus an angle.
 
I'm curious why two fixes are required to create a course leg given that (with TSO C146a navigators) one of the 23 supported leg types is "course to a fix". Course to fix only requires one waypoint plus an angle.
Not all GPS's are 146a-certified. 129 boxes must have that extra waypoint, and all the approaches must be usable by the 129 boxes.
 
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