Instrument App Fix ID Legalities

[Bernoulli Fan]

Regarding the VOR/DME-21 at 6B6:
http://flightaware.com/resources/airport/6B6/IAP/VOR_DME+RWY+21

1. Can you use the GDM-104 to identify the FAF as you track the MHT-210 southwest bound? If not, where does it say feeder routes are not for identifying intersections? I cannot find it in the TERPS legend, the Instrument Flying Handbook, the Instrument Procedures Handbook, or the AIM.

2. If you are using an IFR current GPS in lieu of DME to shoot the approach, can you identify the MAP using the GPS waypoint "RW21"? In other words, does the required DME have to be from MHT? Or can you use 0.0 from RW21? Remember, "GPS" is not part of the approach name.

Thanks for input.

 

[tgrayson]

Can you use the GDM-104 to identify the FAF as you track the MHT-210 southwest bound?

Sure; the thin line with the arrow indicates the radial defines EGORE.

feeder routes are not for identifying intersections?

Feeder routes alone do not define intersections.

can you identify the MAP using the GPS waypoint "RW21"?

Without explicit permission in the AIM that you can do so, I'd vote for "no".

 

[jhugz]

Without explicit permission in the AIM that you can do so, I'd vote for "no".

I'm pretty sure you can. The runway is the missed app point so instead of the GPS saying 25.1 DME off of MHT it draws a GPS way point 25.1 DME off of MHT but it's 0.0 on the approach.

To lazy to look it up tonight so I'm not legal bound by that answer.

 

[tgrayson]

so instead of the GPS saying 25.1 DME off of MHT it draws a GPS way point 25.1 DME off of MHT but it's 0.0 on the approach.

The problem is that the fix is pulled from the database for an approach that contains no overlay, hence only for monitoring purpose, unless the OP is proposing to load some other approach for that runway. I don't see this as an allowable substitution in the AIM, paragraph 1-2-3. Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes.

 

[400A]

From the AIM 1-2-3 a(2)

2. When a VOR, DME, VORTAC, VOR/DME, TACAN, NDB, or compass locator facility including locator outer marker and locator middle marker is operational and the respective aircraft is equipped with operational navigation equipment that is compatible with conventional navaids. For example, if equipped with a suitable RNAV system, a pilot may fly a procedure or route based on operational VOR using RNAV equipment but not monitor the VOR. This category of use is referred to as “alternate means of navigation.”

I could very well be completely reading over it,or understanding the above paragraph wrong. As I read it and the appropriate sections of the AIM, you can use your RNAV system to ID a DME waypoint, you just can't use the GPS/RNAV system for lateral navigation on a non-GPS approach.

1. Determine aircraft position over or distance from a VOR (see NOTE 4 below), TACAN, NDB, compass locator, DME fix; or a named fix defined by a VOR radial, TACAN course, NDB bearing, or compass locator bearing intersecting a VOR or localizer course.

Note 4 isn't applicable.

 

[tgrayson]

ur RNAV system to ID a DME waypoint

This doesn't address the OP's question. He wants to know if he can use the pseudo-fix "RW21" supplied by the GPS database for the missed approach point. I believe he is well aware he can use the GPS as a substitute for DME.

 

[400A]

I might be misunderstanding the question. Is there a GPS approach waypoint to the runway that is named RW21 and he wants to shoot the VOR approach but use the MAP from another approach? OR, is he wanting to make a waypoint named RW21 and define it as MHT 210 @ 25.1?

 

[tgrayson]

Is there a GPS approach waypoint to the runway that is named RW21 and he wants to shoot the VOR approach but use the MAP from another approach

Probably that. Or, many GPS's contain overlays that aren't approved; when you load them, they flash a warning that the approach is for monitoring only and the pilot must use the underlying navaid for navigation.

 

[Bernoulli Fan]

Probably that. Or, many GPS's contain overlays that aren't approved; when you load them, they flash a warning that the approach is for monitoring only and the pilot must use the underlying navaid for navigation.

Yes, it's an unapproved (for monitoring only) GPS overlay approach, not a fix from another approach.

As for the feeder route, when you say it doesn't define an intersection by itself, I'm assuming you just mean you need the MHT-210 as well (of course).

Instead of the GPS saying 25.1 DME off of MHT it draws a GPS way point 25.1 DME off of MHT but it's 0.0 on the approach.

Really? Is that the way the GPS is programmed to identify DME fixes? I have no idea, but that would surprise me. I would expect that all fixes are defined by a lat/long position in the database.

 

[tgrayson]

I'm assuming you just mean you need the MHT-210 as well (of course).

No, I mean that there are TWO lines from GDM, one thick, one thin. The thick is a feeder route and having it alone does not provide a cross radial to define a fix. The thin line is the one that helps define the fix. Often, you will see both together, but not always.

 

[Bernoulli Fan]

No, I mean that there are TWO lines from GDM, one thick, one thin. The thick is a feeder route and having it alone does not provide a cross radial to define a fix. The thin line is the one that helps define the fix. Often, you will see both together, but not always.

Ok, good. Where does it say feeder routes do not define a fix? And why does the thin line not cross the final approach course as most intersection-identifying cross radials do?

 

[ghogue]

1. Can you use the GDM-104 to identify the FAF as you track the MHT-210 southwest bound? If not, where does it say feeder routes are not for identifying intersections? I cannot find it in the TERPS legend, the Instrument Flying Handbook, the Instrument Procedures Handbook, or the AIM.

Thanks for input.

I don't think the GDM104 is allowed to identify EGORE because it (EGORE) is not designated an intersection. If it was, it would be labeled EGORE INT MHT 20. Scan through a few other approaches and you'll see what I'm talking about.

Also, if you refer to FAA Order JO 7350.8H Location Identifiers, it identifies EGORE like this:

EGORE MA
MHT*D*210.00/20.00 42-32-47.0500N 071-29-10.4900W

It only identifies EGORE by DME from MHT and the lat/lon. This might be an error on the chart, but it's the same in the book. That would mean a double error, or I could be wrong and it's an exception to the rule.

BTW, I'm not implying a pilot needs to have a copy of the 7350.8H with them, I certainly never have. It's just a good source of looking this info up.

I'm also thinking that GDM is incorrectly identified as an IAF. The route from GDM should be a feeder and not an initial segment. Feeders lead to IAF's, in this case to EGORE, where you would fly the HILPT. If GDM were correctly an IAF, it would have NoPT in the segment (which it can't because of the 106° turn onto final), as does the route from MHT. What I'm saying is, it makes no sense to have an IAF lead to another IAF that requires a course reversal, that's the purpose of a feeder route.

 

[Pilot Hopeful]

Does Note #3 under AIM 1-2-3(c) provide clarification regarding the use of RW21 as the MAP?

Pilots may not substitute for the navigation aid providing lateral guidance for the final approach segment. This restriction does not refer to instrument approach procedures with “or GPS” in the title when using GPS or WAAS.

We might argue that the DME portion of the navaid is independent of lateral navigation. Then we could use the GPS to identify the MAP: RW21.

However, we are cautioned in AIM 1-1-19(n.8):

Do not attempt to fly an approach unless the procedure is contained in the current, on-board navigation database and identified as "GPS" on the approach chart. The navigation database may contain information about nonoverlay approach procedures that is intended to be used to enhance position orientation, generally by providing a map, while flying these approaches using conventional NAVAIDs. [. . .] Flying point to point on the approach does not assure compliance with the published approach procedure.

While the approach plan view would seem to suggest that RW21 and the approach MAP are coincident, we should not make this assumption.

 

[tgrayson]

Where does it say feeder routes do not define a fix?

Well, nowhere specifically, but you can clearly see that this is the case because many feeder routes are not perpendicular enough to the intersecting course to provide a good enough fix. The more parallel the courses are and the further away the navaid, the sloppier the fix is. For a holding fix, as in this procedure, TERPS requires a minimum of 45 degrees. There must be some way of distinguishing these radials that provide routes and those that define fixes, and the thick vs thin course lines are the way it's done.

And why does the thin line not cross the final approach course as most intersection-identifying cross radials do?

First, I note ghogue's objection and I think it's valid. But also observe in the profile view, the missed approach icons, and EGORE is listed as "EGORE INT". But again, in the missed approach description at the top, it isn't denoted as an intersection. A discrepancy, it seems. Is it an intersection or not? I would argue that the aircraft on the feeder route from GDM has no way of identifying EGORE without an intersection; the DME value is intended to be used when established on the course along which the DME is defined.

IF the fix is an intersection, it is required that the thin line go all the way to the fix? I agree that it usually does, but don't know that it's required; sometimes the chart designer has a lot of latitude in the way things are depicted in order to reduce chart clutter. Doesn't really seem a factor here though.

I'll call the FAA's Flight Procedures Branch on Monday to clear up the intersection issue, unless you would prefer to do it.

 

[Bernoulli Fan]

Heck, Monday's my day off. I'll let you do the work.

Thanks for all the good knowledge in your replies. Unfortunately, it turns out my boss was right and I was wrong. :dunno:

 

[BillPerryCFI]

According to the FAA,

Effective July 16, 1998, pilots may substitute IFR-certified GPS receivers for DME and ADF avionics for all operations except NDB approaches without a GPS overlay. GPS can be used in lieu of DME and ADF on all localizer-type approaches as well as VOR/DME approaches, including when charted NDB or DME transmitters are temporarily out of service.


There was however a few limitations that came along with it.

1. NDB approaches that do not have an associated GPS overlay approach must still be flown using an ADF.
2. A non-GPS approach procedure must exist at the alternate airport when one is required to be filed by regulation. If the non-GPS approaches on which the pilot must rely require DME or ADF, the aircraft must be equipped with DME or ADF avionics as appropriate. GPS substitution for DME/ADF is not permitted in this case.
3. DME transmitters associated with a localizer may not be retrievable from your GPS until the manufacturer incorporates them in the database. Pilots are not authorized to manually enter coordinates. (this however is pretty much well taken care of by now given the fact that this was written 11 years ago)

The key with using GPS is that you have to verify the location that your distance information is coming from in order to use it by retrieving it from the current database. As long as it is done that way instead of manually entering the waypoints lat/long coordinates, this is legal according to the FAA.

I would also recommend as reading the AC90-105. It came out in January of this year and completely replaced the previous GPS in lieu of Advisory Circulars including AC90-94.

One last note is that a lot of people forget that if you are going to be filing your IFR flight plan as /G you are required to verify for your intended route and usage the integrity of GPS RAIM coverage which can be found at www.raimprediction.net

 

[ghogue]

First, I note ghogue's objection and I think it's valid. But also observe in the profile view, the missed approach icons, and EGORE is listed as "EGORE INT". But again, in the missed approach description at the top, it isn't denoted as an intersection. A discrepancy, it seems. Is it an intersection or not? I would argue that the aircraft on the feeder route from GDM has no way of identifying EGORE without an intersection; the DME value is intended to be used when established on the course along which the DME is defined.

IF the fix is an intersection, it is required that the thin line go all the way to the fix? I agree that it usually does, but don't know that it's required; sometimes the chart designer has a lot of latitude in the way things are depicted in order to reduce chart clutter. Doesn't really seem a factor here though.

tgrayson,

I'm sure you're correct about what I highlighted in red above. I think it needs to be an intersection coming from GDM in order to ID EGORE, but I think (and I do not profess to be an expert in TERPS) it may not meet the standards for an intersection when being used as the FAF and therefore they do not list it as an intersection because of this.

I would research TERPS a bit more closely, but instead, I think I'll just wait and see what you find out from the Flight Procedures Branch next week.

gary

 

[tgrayson]

it turns out my boss was right and I was wrong.

Don't be too quick to give up. These topics are often like peeling onions, which is what makes them interesting. Simple questions sometimes result in NOTAMS being issued within a day.

Instrument procedures are actually designed by entering data in forms, rather than drawing them on paper. The chart makers are the ones that take the forms and convert them to pictures, which is why Jepp pictures differ somewhat from NACO's. While the pictures are easier to read, they lack the precision of textual data, particularly since the chart makers don't provide us with a rigorous description of their methodology.

You may find this article pertinent to this discussion.

 

[Hubbs]

According to the FAA,

Effective July 16, 1998, pilots may substitute IFR-certified GPS receivers for DME and ADF avionics for all operations except NDB approaches without a GPS overlay. GPS can be used in lieu of DME and ADF on all localizer-type approaches as well as VOR/DME approaches, including when charted NDB or DME transmitters are temporarily out of service.


There was however a few limitations that came along with it.

1. NDB approaches that do not have an associated GPS overlay approach must still be flown using an ADF.
2. A non-GPS approach procedure must exist at the alternate airport when one is required to be filed by regulation. If the non-GPS approaches on which the pilot must rely require DME or ADF, the aircraft must be equipped with DME or ADF avionics as appropriate. GPS substitution for DME/ADF is not permitted in this case.
3. DME transmitters associated with a localizer may not be retrievable from your GPS until the manufacturer incorporates them in the database. Pilots are not authorized to manually enter coordinates. (this however is pretty much well taken care of by now given the fact that this was written 11 years ago)

The key with using GPS is that you have to verify the location that your distance information is coming from in order to use it by retrieving it from the current database. As long as it is done that way instead of manually entering the waypoints lat/long coordinates, this is legal according to the FAA.

I would also recommend as reading the AC90-105. It came out in January of this year and completely replaced the previous GPS in lieu of Advisory Circulars including AC90-94.

One last note is that a lot of people forget that if you are going to be filing your IFR flight plan as /G you are required to verify for your intended route and usage the integrity of GPS RAIM coverage which can be found at www.raimprediction.net

Related GPS substitution question:

Can you use an IFR certified GPS with an out-of-date database as a substitute for ADF? For example, on an ILS/LOC with a compass locator as the IAF/FAF and also Missed Approach holding point, if you verify the Lat/Long of the LOM can you still make the substitution?

 

[Bernoulli Fan]

Related GPS substitution question:

Can you use an IFR certified GPS with an out-of-date database as a substitute for ADF? For example, on an ILS/LOC with a compass locator as the IAF/FAF and also Missed Approach holding point, if you verify the Lat/Long of the LOM can you still make the substitution?

No.