NDB approach using GPS

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James Hines

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James
Looking for advise on flying an approach. My IFR navigator (IDF540) has the ability to fly NDBs. It has the MAP as a GPS fix. Do you legally need to time it or can you use the fix to know when to go missed.
 
AIM 1-2-3 is your reference. You can use GPS to identify any fix on a procedure. The MAP is one of those.

But, implied in your question is that you can use the GPS to fly the NDB procedure, and that is not quite correct. You cannot completely substitute GPS for NDB final course guidance, you must have an ADF receiver tuned to the NDB in order to fly it. Though you can fly it using the GPS for guidance and just be "monitoring" the ADF.
 
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RussR said:
AIM 1-2-3 is your reference. You can use GPS to identify any fix on a procedure. The MAP is one of those.

But, implied in your question is that you can use the GPS to fly the NDB procedure, and that is not quite correct. You cannot completely substitute GPS for NDB final course guidance, you must have an ADF receiver tuned to the NDB in order to fly it. Though you can fly it using the GPS for guidance and just be "monitoring" the ADF.
Click to expand...

My question was actually if you need to time. You are allowed to use GPS to fly a NDB approach if it has a GPS overlay.
 
James Hines said:
Looking for advise on flying an approach. My IFR navigator (IDF540) has the ability to fly NDBs. It has the MAP as a GPS fix. Do you legally need to time it or can you use the fix to know when to go missed.
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Are you outside the U.S.? There are literally no NDB approaches in the U.S. that don’t have at least a GPS overlay, and most have a standalone RNAV GPS approach serving the runway (or airport, in the case of a circling approach).
 
Brad Z said:
Are you outside the U.S.? There are literally no NDB approaches in the U.S. that don’t have at least a GPS overlay, and most have a standalone RNAV GPS approach serving the runway (or airport, in the case of a circling approach).
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No Sir, I'm in the U.S. I wanted to shoot one today for 'fun'.
 
James Hines said:
My question was actually if you need to time. You are allowed to use GPS to fly a NDB approach if it has a GPS overlay.
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That was the first part of his answer...
AIM 1-2-3 is your reference. You can use GPS to identify any fix on a procedure. The MAP is one of those.
Click to expand...
But the second part revolves around what you’re thinking is a “GPS overlay” that very possibly isn’t.
 
Brad Z said:
Does the IDF540 have an AM NDB receiver? How do you fly the final approach course?
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IFD540 has an option to select the NDB approach for the RWY. No NDB receiver just done by overlay, so to speak.
 
James Hines said:
IFD540 has an option to select the NDB approach for the RWY. No NDB receiver just done by overlay, so to speak.
Click to expand...
So is it an “overlay” with “OR GPS” in the tittle on the approach chart, or is it an “overlay so to speak” without “OR GPS” in the title that cannot be legally flown with just GPS?
 
James Hines said:
IFD540 has an option to select the NDB approach for the RWY. No NDB receiver just done by overlay, so to speak.
Click to expand...
Sounds like it can’t be used to fly an NDB approach..only a GPS overly (“or GPS”) which is a GPS procedure, not a NDB procedure. You do not use time to identify MAPs on GPS approaches; the equipment will sequence you to the missed approach segment automatically. No harm in starting a timer, but that’s for your own situational awareness; not as a means to go missed.
 
James Hines said:
My question was actually if you need to time. You are allowed to use GPS to fly a NDB approach if it has a GPS overlay.
Click to expand...

True, but a "GPS overlay" means the procedure is named "NDB OR GPS RWY xxx", which if that's the case, you didn't mention it in your OP, and yes that would be perfectly okay to fly with only a GPS.

Brad Z said:
Are you outside the U.S.? There are literally no NDB approaches in the U.S. that don’t have at least a GPS overlay, and most have a standalone RNAV GPS approach serving the runway (or airport, in the case of a circling approach).
Click to expand...

The use of a double negative is a bit confusing, but it seems like you are saying "all NDB approaches have overlays". Since "GPS overlay" means "NDB OR GPS RWY xx", your statement that there are none without "OR GPS" is easily proved incorrect. Took me no time at all to find one, KSRE NDB RWY 16. In fact, there are very few "NDB or GPS" procedures in the U.S... I count 7.

AIM 1-1-17, a few pages into that long paragraph:
5. GPS Instrument Approach Procedures
(a) GPS overlay approaches are designated non−precision instrument approach procedures that pilots are authorized to fly using GPS avionics. Localizer (LOC), localizer type directional aid (LDA), and simplified directional facility (SDF) procedures are not authorized. Overlay procedures are identified by the “name of the procedure” and “or GPS” (e.g., VOR/DME or GPS RWY 15) in the title.

The mere existence of an RNAV (GPS) to the same runway as an NDB approach, or the existence of the NDB approach in a GPS's database, does not make it a "GPS overlay".
 
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GPS can not be used for lateral guidance inside the FAF for an ground based approach unless labled or GPS.

There are provisions in Part 135/121 to allow GPS as sole source for NDB & VOR approaches.. but it takes some worm to get approved.


Sent from my SM-G975U using Tapatalk
 
RussR said:
AIM 1-2-3 is your reference. You can use GPS to identify any fix on a procedure. The MAP is one of those.

But, implied in your question is that you can use the GPS to fly the NDB procedure, and that is not quite correct. You cannot completely substitute GPS for NDB final course guidance, you must have an ADF receiver tuned to the NDB in order to fly it. Though you can fly it using the GPS for guidance and just be "monitoring" the ADF.
Click to expand...
I saw a number of answers which touched on it but lets go back to this one which says it.

It is exactly the same rule as for VOR approaches. Subject to any limitations which may appear the the unit AFMS, GPS may be used to navigate on the FAS of a "pure" NDB approach so long as you also have an ADF receiver tuned in and providing "raw" course data.
James Hines said:
My question was actually if you need to time.
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Assuming your GPS identifies a MAP when you load the approach, no*.

Here's my view on timing on any approach. The distance from FAF to MAP is regulatory. The timing table is not. The timing table is just a simple T=D/S calculation. That's why the FAA and Jepp charts have some different GS numbers. It's informational only and they choose to display the calculations for different speeds. Plus, since wind can (and does) change as you descend on an approach, your GS changes (assuming you actually calculated GS to begin with) , so unless you are adjusting your time all along the way, at best it is just an estimate. So your choice is, use your guestimated time to the MAP or its regulatory location displayed on the GPS. I know what mine is :)

*Edited by someone who wasn't quite awake when he wrote it.
 
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RussR said:
True, but a "GPS overlay" means the procedure is named "NDB OR GPS RWY xxx", which if that's the case, you didn't mention it in your OP, and yes that would be perfectly okay to fly with only a GPS.



The use of a double negative is a bit confusing, but it seems like you are saying "all NDB approaches have overlays". Since "GPS overlay" means "NDB OR GPS RWY xx", your statement that there are none without "OR GPS" is easily proved incorrect. Took me no time at all to find one, KSRE NDB RWY 16. In fact, there are very few "NDB or GPS" procedures in the U.S... I count 7.
Click to expand...

What I'm saying is that if a runway or airport is served by an NDB approach, there is always a GPS option, either an RNAV (GPS) approach to the same runway, or an overlay with the NDB approach. As you noted, there are very few overlays remaining; they have been replaced with standalone RNAV approaches. But my point is is that the OP has no reason to fly an NDB approach with his GPS navigator; there is an appropriate satellite-based approach available as an alternative.
 
Brad Z said:
What I'm saying is that if a runway or airport is served by an NDB approach, there is always a GPS option, either an RNAV (GPS) approach to the same runway, or an overlay with the NDB approach. As you noted, there are very few overlays remaining; they have been replaced with standalone RNAV approaches. But my point is is that the OP has no reason to fly an NDB approach with his GPS navigator; there is an appropriate satellite-based approach available as an alternative.
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I agree but theoretical discussions can be helpful for understanding.
 
midlifeflyer said:
I agree but theoretical discussions can be helpful for understanding.
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And I would also state that asserting that all NDB approaches have GPS overlays is confusing and false, even if it is true that any airport with an NDB approach will also have at least one alternate approach that may be legally flown by reference to GPS guidance alone.
 
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