VNAV and Pseudo RNAV Approach

[Pilot101]

Greetings,

There are a lot of super smart pilots with lots of GTN experience on this forum so I am sure I came to the right place for this question...

I have the Dynon SkyView SV-1000 EFIS and a Garmin GTN-650 that I am just now learning how to integrate together.

At my home airport there is no instrument approach procedure and it is very dark at night because it is located in a very small community and it has lots of scary looking mountains all around (does not look so scary at night because you can not see the mountains) so can someone please tell me how to design my own Pseudo RNAV Approach on the GTN?

The idea is to make up the approach and to save it as a memorized flight and pull it up at the end of the flight during descent and then direct nav to the first fix and altitude of the saved "approach" and sit back and watch the show...

I would not use it in IMC but this airport is very remote and it is super dark at night so if I can design the "approach" to fly down the valley and cross the FAF at a certain altitude and a 3 degree glide path to the runway that would be very helpful for CFIT avoidance...and make flying just that much more fun...

THANKS!!!

 

[luvflyin]

Greetings,

There are a lot of super smart pilots with lots of GTN experience on this forum so I am sure I came to the right place for this question...

I have the Dynon SkyView SV-1000 EFIS and a Garmin GTN-650 that I am just now learning how to integrate together.

At my home airport there is no instrument approach procedure and it is very dark at night because it is located in a very small community and it has lots of scary looking mountains all around (does not look so scary at night because you can not see the mountains) so can someone please tell me how to design my own Pseudo RNAV Approach on the GTN?

The idea is to make up the approach and to save it as a memorized flight and pull it up at the end of the flight during descent and then direct nav to the first fix and altitude of the saved "approach" and sit back and watch the show...

I would not use it in IMC but this airport is very remote and it is super dark at night so if I can design the "approach" to fly down the valley and cross the FAF at a certain altitude and a 3 degree glide path to the runway that would be very helpful for CFIT avoidance...and make flying just that much more fun...

THANKS!!!

If you're looking to get +V like advisory needles, I'm sure there is no way. The GPS box manufactures would be insane to allow that. DISCLAIMER: I ain't saying this is wise. Put in the Lat/Long coordinates you want. The 650 will sequence from one to the next. Now get pen and paper and note the altitude you want at each. A kind of DIY Approach Plate. On second thought, don't do this.

 

[chemgeek]

Probably the safest thing to do is to set up a custom waypoint on the final approach course at which you know you can arrive at a safe altitude to commence a safe visual approach from. If the runway lighting system disappears on final approach, there is cumulogranite between you and the runway. Yo are not going to be able to onfigure your box to give you vertical guidance on the CDI for your custom routing. But you could use the GTN to provide horizontal guidance along an extended runway centerline whose terrain features are known to you for a safe visual approach. But regardless, you are going to be flying a visual approach.

My airport is in a black hole between two 500 foot ridges and (often unlit) 250 foot windmills near the departure end of one runway and a substantial hill off the end of the other runway. I don't like flying visual approaches into it at night, even VFR, and will usually fly the IFR procedure to assure terrain avoidance. The FAA does a lot of work to ensure safe terrain clearance for IFR approaches while maintaining reasonable descent rates.

 

[asicer]

If you have a later version of the GTN650 software, it should have a visual approach feature that puts up a "visual approach" button as you get closer to the airport. Selecting that gets you lateral/vertical guidance on your CDI/HSI. You can see it in this video (I believe it also shows that you can add it to your flight plan):

Leading up to that, you should be able add VNAV to your flight plan leading up to your fake final approach fix.

 

[LesGawlik]

If you're looking to get +V like advisory needles, I'm sure there is no way. The GPS box manufactures would be insane to allow that. DISCLAIMER: I ain't saying this is wise. Put in the Lat/Long coordinates you want. The 650 will sequence from one to the next. Now get pen and paper and note the altitude you want at each. A kind of DIY Approach Plate. On second thought, don't do this.

Why not? If you are not going to violate VFR minimums and fly cheat IFR, it's just an aid to situational awareness. I could see where it would be valuable on a perfectly legal night flight. If it gives you a temptation to do something wrong so strong you can't avoid it, you have the wrong (a)vocation.

 

[luvflyin]

If you have a later version of the GTN650 software, it should have a visual approach feature that puts up a "visual approach" button as you get closer to the airport. Selecting that gets you lateral/vertical guidance on your CDI/HSI. You can see it in this video (I believe it also shows that you can add it to your flight plan):

Leading up to that, you should be able add VNAV to your flight plan leading up to your fake final approach fix.

Does this work if there are no published Approaches to the airport?

 

[asicer]

Does this work if there are no published Approaches to the airport?

Yes.

 

[luvflyin]

Why not? If you are not going to violate VFR minimums and fly cheat IFR, it's just an aid to situational awareness. I could see where it would be valuable on a perfectly legal night flight. If it gives you a temptation to do something wrong so strong you can't avoid it, you have the wrong (a)vocation.

Yeah. I was being cautious about advocating making up Roll yer Own Approaches lest I be accused of giving bad advice.

 

[RussR]

There are several ways, depending on the software version of your GTN 650.
- Construct user waypoints at, say 3nm final and plan to cross at 1000' above the runway elevation.
- Use the VNAV function, from a known point on final.
- Use the Visual approach function.

Some will even give you a glideslope to follow. But, of course remember that standard instrument approach procedures have all kinds of buffer zones and safety factors built in, that you (likely) wouldn't know about. And the roll-your-own procedures will not.

So if this is a public-accessible airport (you didn't say), why not ask the FAA to design an actual approach for it? Having it usable at night will require an airport obstruction survey, but there may even be state/etc funds for that.

 

[asicer]

Some will even give you a glideslope to follow. But, of course remember that standard instrument approach procedures have all kinds of buffer zones and safety factors built in, that you (likely) wouldn't know about. And of the roll-your-own procedures will not.

I've noticed that the visual approach function sometimes gives you a 3degree glidepath where the the VASI/PAPI is greater than 3 degrees, so buyer beware!
(the manual says that it builds the visual approach from the terrain database)

 

[luvflyin]

I've noticed that the visual approach function sometimes gives you a 3degree glidepath where the the VASI/PAPI is greater than 3 degrees, so buyer beware!
(the manual says that it builds the visual approach from the terrain database)

This just slapping up glide path needles to just any old runway wasn’t sitting right with me. Started looking around and after reading what basically amounted to Garmins Press Releases on many different websites I found this. It includes quotes from the Pilot Guides, seems to explain it pretty well and passes the logic check.
https://www.avsim.com/forums/topic/575475-visual-approach-glideslope-feature/

 

[aterpster]

Some will even give you a glideslope to follow. But, of course remember that standard instrument approach procedures have all kinds of buffer zones and safety factors built in, that you (likely) wouldn't know about. And the roll-your-own procedures will not.

I have a GIS program with topos for many of the states. I also have access to the DOF and know how to use it. Big deal. I can't get the navigator to do ad hoc LPV. And, not even LNAV/VNAV with the required final segment level of alerting.

 

[RussR]

I have a GIS program with topos for many of the states. I also have access to the DOF and know how to use it. Big deal. I can't get the navigator to do ad hoc LPV. And, not even LNAV/VNAV with the required final segment level of alerting.

Yes, but you're hardly at the typical pilot knowledge level on this stuff.

And the newer GA avionics will most definitely plot a 3 deg (or whatever you choose) glidepath to any runway, and give you horizontal and vertical guidance that an autopilot can follow with just a couple button presses. What they use for signal integrity and alerting levels I have no idea. Nor do I know if they will allow you to plot a course that goes through a mountain.

 

[luvflyin]

Yes, but you're hardly at the typical pilot knowledge level on this stuff.

And the newer GA avionics will most definitely plot a 3 deg (or whatever you choose) glidepath to any runway, and give you horizontal and vertical guidance that an autopilot can follow with just a couple button presses. What they use for signal integrity and alerting levels I have no idea. Nor do I know if they will allow you to plot a course that goes through a mountain.

A GTN650 won’t always give Vertcal Guidance to any Runway. Certain conditions must be met. It must have a valid Terrain Data Base to do it at all.

 

[Ryan F.]

For what you're describing, I'd be hesitant to use the Navigator for anything other than lateral alignment with the runway centerline, and even then only in a "backup" sense (be able to see the runway.)

You really have to think about the worst-case scenario every single time; you have to assume a tower might have been constructed, or some other change with the terrain/obstacles you're dealing with has occurred since the last time you flew into the airport.

In good VMC, and flying VFR, I've tried tracking the LNAV+V vertically past the FAF to my backwoods home drome. If I followed it to one of the runways my landing gear would get tangled up with the branches of a tall tree located right on the extended runway centerline.

 

[RussR]

In good VMC, and flying VFR, I've tried tracking the LNAV+V vertically past the FAF to my backwoods home drome. If I followed it to one of the runways my landing gear would get tangled up with the branches of a tall tree located right on the extended runway centerline.

A great example of why it’s important for people to understand that there is not necessarily any protection from obstacles below the MDA on any non-vertically guided approach (LP, LNAV, LOC, VOR, NDB, etc). If you descend below the MDA, you are now on a visual segment of the procedure and are responsible for your own obstacle clearance.

 

[Pilot101]

My home airport is very remote and it is very dark and we do have a lot of mountains nearby. The runway has lights but no PAPI so even though I know the terrain the night VMC approach does increase the pucker factor so I would like to build a approach path with VNAV that I can follow and have a backup reference. The safest approach at night is to fly over the airport and enter the downwind.

I could just enter user waypoints while flying the visual however I would like to play around with building the approach a bit more scientifically...Has anyone used Google Earth to do something like this? I imagine you could click the locations of the places where you want to place a user waypoint and then an altitude and it could even give you height above known obstructions and terrain.

So using the GTN (or Google Earth)... if I taxi down the runway and park on the numbers the GPS will give me LAT and LONG for that position...and I know the altitude...so how do I work backwards to project a point in space 3 NM and 1000 HAT behind me...then the downwind etc?

If anyone has done this I would appreciate the head start...

THANKS!!!

 

[rosssr20]

If I wanted to do something like this, I would fly the profile I desired during the day and record it using the GTN then download the data file off the SD card, open it in excel and select a few step downs based on time (workload permitting maybe 30 second intervals) down to 3mi from the rw threshold. This will give me a bunch of gps locations and corresponding altitudes to pick from. Then use this method to import the waypoints:
https://support.garmin.com/en-US/?faq=3mcdU37gXi88ipwjJIxJo7
https://support.garmin.com/en-US/?faq=3mcdU37gXi88ipwjJIxJo7

Then you can make a flight plan with altitudes and store it on the GTN. The waypoints won’t store altitudes so you can just add the crossing altitudes when you setup the flight plan.

Then I would fly that flight plan during the day and see if it works.

It won’t be loaded as a procedure but as a flight plan.

 

[Hang 4]

Has anyone used Google Earth to do something like this? I imagine you could click the locations of the places where you want to place a user waypoint and then an altitude and it could even give you height above known obstructions and terrain.

I doubt Google Earth has obstruction heights. Think it just does an MSL estimation of the surface.

 

[flyingron]

You might invest your time/money into putting some PCL lighting in place or even a makeshift VASI. I actually have a military portable VASI but by the time we think about setting it up in the evening (the best place would be directly opposite the airport bar), we've always been into the margaritas by the time anybody thinks about test flying it.