Why would an overlay stop being an overlay?

[TMetzinger]

I found something interesting - the VOR-A approach in to KOKV used to be an overlay (VOR/DME or GPS-A) and is now not an overlay (VOR/DME-A). As far as I can see, there haven't been any changes other than the course being 1 degree different - the waypoints are the same so I assume the cours difference is related to the change in variation over time.

So why would this approach be no longer flyable using GPS? Hasn't been re-surveyed?

 

[roncachamp]

I found something interesting - the VOR-A approach in to KOKV used to be an overlay (VOR/DME or GPS-A) and is now not an overlay (VOR/DME-A). As far as I can see, there haven't been any changes other than the course being 1 degree different - the waypoints are the same so I assume the cours difference is related to the change in variation over time.

I've observed overlay approaches being dropped when standalone GPS approaches are published that effectively replace them. Lost three that way at KMNM last cycle. Looks like there are two new straight-in GPS procedures at KOKV, that's probably what led to it. The policy doesn't make a lot of sense. What was gained by removing "or GPS" from the procedure name?

So why would this approach be no longer flyable using GPS? Hasn't been re-surveyed?

It's still flyable using GPS, as long as you have a VOR receiver and MRB VOR/DME is operating. But now the procedure is unavailable if the VOR is out of service even if you have GPS.

 

[wsuffa]

I've observed overlay approaches being dropped when standalone GPS approaches are published that effectively replace them. Lost three that way at KMNM last cycle. Looks like there are two new straight-in GPS procedures at KOKV, that's probably what led to it. The policy doesn't make a lot of sense. What was gained by removing "or GPS" from the procedure name?

I wouldn't call 'em "new", the GPS 14 has been around for a while. They may have added a new waypoint on the North side.

It's still flyable using GPS, as long as you have a VOR receiver and MRB VOR/DME is operating. But now the procedure is unavailable if the VOR is out of service even if you have GPS.

No real reason to have it w/GPS now that there are the straight-in GPS approaches. Saves some flight-checking.

 

[poadeleted20]

What was gained by removing "or GPS" from the procedure name?

The cost of flight checking the GPS portion of the approach.

It's still flyable using GPS, as long as you have a VOR receiver and MRB VOR/DME is operating.

While you can fly most of the approach using the GPS, you have to use the VOR for lateral nav on the final segment.

But now the procedure is unavailable if the VOR is out of service even if you have GPS.

While that's true, I can't think of any reason why someone with an IFR approach GPS would want to fly a circling-only approach when straight-in RNAV(GPS) approaches with lower mins are available to both ends of the only runway at that airport.

 

[TMetzinger]

Since the straight in approaches have been around for a while, cost-savings makes the most sense.

Thanks!

 

[roncachamp]

I wouldn't call 'em "new", the GPS 14 has been around for a while. They may have added a new waypoint on the North side.

"Orig 09239", that's August 27 2009.

No real reason to have it w/GPS now that there are the straight-in GPS approaches. Saves some flight-checking.

Why would it save any flight checking? Are separate flight checks required for the GPS and traditional NAVAID portions of overlay approaches?

 

[roncachamp]

The cost of flight checking the GPS portion of the approach.

Are separate flight checks required for the GPS and traditional NAVAID portions of overlay approaches?

While that's true, I can't think of any reason why someone with an IFR approach GPS would want to fly a circling-only approach when straight-in RNAV(GPS) approaches with lower mins are available to both ends of the only runway at that airport.

To save time.

 

[wsuffa]

"Orig 09239", that's August 27 2009.

I've flown a GPS-14 into KOKV regularly since 2003. In fact, you'll find it in my logbook from June of this year when I did my last IPC... SOGBE, BONCI, WOGDI, etc were waypoints on the approach.

The approach may be redesignated as RNAV (instead of just GPS), and I don't recall an LPV on it, but it did exist in essentially the same form.

Why would it save any flight checking? Are separate flight checks required for the GPS and traditional NAVAID portions of overlay approaches?

AFAIK, yes.

 

[roncachamp]

AFAIK, yes.

Sounds like you're guessing.

 

[wsuffa]

Sounds like you're guessing.

Last time I rode in a flight check aircraft was before GPS was common. At the time, they had to check each navaid and each limit on every listed approach. Part of the reason for doing that was to look for interference that impacted a portion of an approach.

GPS is more susceptable to interference than most people know (and it's not just blocking, it's also spoofing). Given that, the only way to know if there is an interference source that affects a portion of a labeled GPS approach is to actually fly it using the navaid involved.

So, yes, it's an educated guess based on experience.

 

[roncachamp]

Last time I rode in a flight check aircraft was before GPS was common. At the time, they had to check each navaid and each limit on every listed approach. Part of the reason for doing that was to look for interference that impacted a portion of an approach.

GPS is more susceptable to interference than most people know (and it's not just blocking, it's also spoofing). Given that, the only way to know if there is an interference source that affects a portion of a labeled GPS approach is to actually fly it using the navaid involved.

So, yes, it's an educated guess based on experience.

Well, my educated guess based on experience gained when GPS is common is that they're done simultaneously.

 

[poadeleted20]

Sounds like a question for my friends in the flight check business.