More info on GNS 430/530 WAAS upgrade

Matt Barrow wrote:


I'd like to dump my KLN94 and go to a GPS480 with an AviDyne MX-500. One
problem is the GPS480 does not support curved flight paths (GAMA) that a GPS
430 does.

It will fly them (at least it does holds, procedure turns, and DME
arcs). Maybe it doesn't reflect htem properly on the GAMA graphcis
to the AVIDYNE (I have an MX20)



I wonder if I should go with a dual GPS in the form of a GPS 430/ 480 combo?
Would it work?



Perhaps but confusing as hell I would think.

Ron Natalie wrote:

Matt Barrow wrote:


I'd like to dump my KLN94 and go to a GPS480 with an AviDyne MX-500. One
problem is the GPS480 does not support curved flight paths (GAMA) that a GPS
430 does.

It will fly them (at least it does holds, procedure turns, and DME
arcs). Maybe it doesn't reflect htem properly on the GAMA graphcis
to the AVIDYNE (I have an MX20)

ARINC 424 specifications provide for two different type of curved legs AF (arc to
fix) and RF (radius to fix). AF legs are for DME ARCs. RF legs are for the new,
advanced instrument approach procedures, which thus far are limited to
RNP-qualified aircraft and flight crews.

Garmin claims their panel mounts will be able to do RF legs, but I remain
skeptical. I can see it working but only in a robust installation with an
electronic HSI (where the course setting auto-slews to keep up with the RF leg's
constant course change) and with a good steering computer for either a flight
director or nav mode of the autopilot.

With an AF leg you have 4 miles of protected airspace (plus a 2 mile secondary)
each side of the ARC, so some plus-or-minus 0.5 mile zig-zagging is
insignificant. Not so with RF legs where not only is the radius of turn typically
much tighter than a DME ARC, the protected airspace may only be 0.6 of a mile each
side of centerline. And, an RF leg of one radius and direction can be immediately
followed by a different RF leg of a different radius and/or direction. This is a
much more complex flight path to manage than a DME ARC or a holding pattern
(Garmin's holding patterns are not real-world patterns in any case; rather just
symbols for holding course and turn direction.)

wrote:


Garmin claims their panel mounts will be able to do RF legs, but I remain
skeptical. I can see it working but only in a robust installation with an
electronic HSI (where the course setting auto-slews to keep up with the RF leg's
constant course change) and with a good steering computer for either a flight
director or nav mode of the autopilot.


With GPSS steering engaged the HSI OBS is ignored and the only reason
you need touch it is to keep the needle oriented right. It reads
left-right of course just fine even on my old steam-gage King HSI.


(Garmin's holding patterns are not real-world patterns in any case; rather just
symbols for holding course and turn direction.)


They're real enough that the autopilot flies them as depicted.

Ron Natalie wrote:

wrote:


Garmin claims their panel mounts will be able to do RF legs, but I remain
skeptical. I can see it working but only in a robust installation with an
electronic HSI (where the course setting auto-slews to keep up with the RF leg's
constant course change) and with a good steering computer for either a flight
director or nav mode of the autopilot.


With GPSS steering engaged the HSI OBS is ignored and the only reason
you need touch it is to keep the needle oriented right. It reads
left-right of course just fine even on my old steam-gage King HSI.

It seems it depends on how the autopilot gets its steering information. The most
common for light aircraft, as I understand it, is to use the value in the OBS window.
Having said that I have no doubt there are other methods of doing it with all the
technology out there.

My concern is that a pilot cannot, should not be able to hand fly an RF leg without at
least a flight director providing valid steering commands.



(Garmin's holding patterns are not real-world patterns in any case; rather just
symbols for holding course and turn direction.)


They're real enough that the autopilot flies them as depicted.

That doesn't make them bear any relationship to the holding pattern containment area
provided by the procedures designer.

wrote:

Ron Natalie wrote:


wrote:

Garmin claims their panel mounts will be able to do RF legs, but I remain
skeptical. I can see it working but only in a robust installation with an
electronic HSI (where the course setting auto-slews to keep up with the RF leg's
constant course change) and with a good steering computer for either a flight
director or nav mode of the autopilot.


With GPSS steering engaged the HSI OBS is ignored and the only reason
you need touch it is to keep the needle oriented right. It reads
left-right of course just fine even on my old steam-gage King HSI.


It seems it depends on how the autopilot gets its steering information. The most
common for light aircraft, as I understand it, is to use the value in the OBS window.
Having said that I have no doubt there are other methods of doing it with all the
technology out there.

I was talking about GPSS. It doesn't even require the aircraft to have
an HSI. The GPS talks directly to the autopilot in digital form.

(Garmin's holding patterns are not real-world patterns in any case; rather just
symbols for holding course and turn direction.)


They're real enough that the autopilot flies them as depicted.


That doesn't make them bear any relationship to the holding pattern containment area
provided by the procedures designer.


The procedure designer doesn't "provide the containment area." He
provides the hold based on the protected area available. The 480
flies the hold either literally as published or when not published
in a manner consistant with the TERPS guideline. Is there some
specific instance you're referring to?

Ron Natalie wrote:



That doesn't make them bear any relationship to the holding pattern containment area
provided by the procedures designer.


The procedure designer doesn't "provide the containment area." He
provides the hold based on the protected area available. The 480
flies the hold either literally as published or when not published
in a manner consistant with the TERPS guideline. Is there some
specific instance you're referring to?

The procedures designer indeed provides the containment area for holding. The criteria are
contained in FAA Order 7130.3A, "Holding Pattern Criteria." The forward to that handbook
states,

"This order primarily serves as a planning document for airspace planners by setting forth
criteria for determining holding pattern airspace area dimensions and instructions for
their use. In addition, it provides application criteria for use by procedures specialists
in developing holding airspace for instrument procedures.
Sufficient holding airspace areas shall be planned and established to meet IFR traffic
requirements within a facility's area of jurisdiction.
Holding airspace areas shall be determined by applying the criteria contained within this
document."

There are 31 different templates used for over 125 combinations of altitude, distance from
facility, type of aircraft, etc. Generally, pattern sizes 4 to 13 for low altitude holding
and holding pattern course reversals on IAPs.

So far as I know there is no RNAV platform today that contains database information or
software routines consistent with the holding patterns developed and documented by the FAA
on airspace record 8260-2 (the form that documents all the details about facilities, fixes,
and waypoints).

As to whether a light aircraft autopilot can track an RF leg (a much, much tigher
requirement than holding pattern or DME ARCs) I passed it by an avionics engineer. The
autopilot has to be roll-steering based. He added that most light aircraft autopilots are
not roll-steering based.

"Ron Natalie" wrote in message
...
Matt Barrow wrote:


I'd like to dump my KLN94 and go to a GPS480 with an AviDyne MX-500. One
problem is the GPS480 does not support curved flight paths (GAMA) that a
GPS
430 does.

It will fly them (at least it does holds, procedure turns, and DME
arcs). Maybe it doesn't reflect htem properly on the GAMA graphcis
to the AVIDYNE (I have an MX20)

That's right...I should have specified that the Avidyne requires a GAMA
conection.



I wonder if I should go with a dual GPS in the form of a GPS 430/ 480
combo?
Would it work?



Perhaps but confusing as hell I would think.

Yeah, but neither has what I want. Darn!

Ron Natalie wrote:
Matt Barrow wrote:


I'd like to dump my KLN94 and go to a GPS480 with an AviDyne MX-500. One
problem is the GPS480 does not support curved flight paths (GAMA) that a GPS
430 does.


It will fly them (at least it does holds, procedure turns, and DME
arcs). Maybe it doesn't reflect htem properly on the GAMA graphcis
to the AVIDYNE (I have an MX20)


WAAS, in the long run, probally has its best advantage if it can do curved
approaches to final. This would eliminate a LOT of the clearance restrictions
on existing approaches.

Scott Moore wrote:

Ron Natalie wrote:



WAAS, in the long run, probally has its best advantage if it can do curved
approaches to final. This would eliminate a LOT of the clearance restrictions
on existing approaches.

WAAS has nothing to do with RF legs (curved approach paths). RF legs are a leg
computation done by an RNAV/LNAV platform. WAAS is an augmentation scheme for
GPS. RF legs are independent of the nav sensor, although GPS is presently the
preferred sensor for RNAV/LNAV. So, there is no reason that a TSO-C146 (WAAS/LPV)
couldn't do RF legs with, or without, WAAS and or LPV.

Having said that, I haven't heard of any proposed implementation along those lines
for WAAS and LPV.