More info on GNS 430/530 WAAS upgrade

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.