Yet more GPS substitution questions

OK, then why have the requirements that prohibit GPS substitution when

picking an alternate for filing?

When you ask why, you are making the assumption that the FAA makes
rules for valid and comprehensible reasons. That's not an assumption
that is supported by the facts

Seriously, the logic, if you can call it that, is that GPS is an
unproven technology, and thus one should have a backup plan that does
not rely on it. The FAA would rather you rely on a 30-year-old ADF
receiver pointing at a WWII-era NDB transmitter.

Getting out of the alternate rathole, any thoughts about the general
rules of GPS substitution, specifically applying them to the questions

I had on the Minuteman approach?

The rules are clear enough - any approved GPS may be substituted for
DME or ADF on any approach except that you may not use a GPS to fly an
NDB approach unless it is an approach-certified GPS being used to fly a
published overlay. Now those are rules. Your question regards
procedures.

As a Part-91 operator, you can pretty much use whatever procedures make
sense to you - if it's not prohibited, it's allowed.

In your particular case, the DME is used in conjunction with the VOR to
identify the IAF/FAF (EGORE, 210 rad 20.0 DME MHT) and the MAP (210 rad
25.1 DME MHT). If you like, you can configure the GPS to point to the
MHT VOR and read distance just as you would off the DME. That would be
fine. Or you can configure it to point to EGORE, and call the MAP at
5.1 from there. That would be fine. Or you can configure it to point
to the MAP, and call 5.1 from that the IAF/FAF. That would be fine.
Or you could write yourself a flight plan that would take you to the
IAF and then the MAP, so you could get a readout of distance counting
down to the IAF/FAF, and then the MAP. That would be fine. And if
someone has already done that for you (in this case the manufacturer
who provided the software for approach monitoring) and you're
comfortable that he did the job properly, that's fine too. Use
whatever procedure works for you.

The question become more interesting when GPS is substituted for ADF,
especially when the NDB is the missed approach holding point. One
option (if available) is to use the missed approach sequencing provided
by the GPS for the approach monitoring function (some will even depict
the hold and tell you which entry to use) but anything you care to do,
up to and including setting up the display to read out the bearng and
distance to the NDB and flying the hold off the numbers is acceptable.

If you would tell us more about what kind of equipment you have in the
cockpit, we might be able to make more intelligent suggestions about
what procedures would be optimal.

Michael

On 11 Feb 2005 11:49:43 -0800, "Michael"
wrote:


In your particular case, the DME is used in conjunction with the VOR to
identify the IAF/FAF (EGORE, 210 rad 20.0 DME MHT) and the MAP (210 rad
25.1 DME MHT). If you like, you can configure the GPS to point to the
MHT VOR and read distance just as you would off the DME. That would be
fine. Or you can configure it to point to EGORE, and call the MAP at
5.1 from there. That would be fine. Or you can configure it to point
to the MAP, and call 5.1 from that the IAF/FAF. That would be fine.
Or you could write yourself a flight plan that would take you to the
IAF and then the MAP, so you could get a readout of distance counting
down to the IAF/FAF, and then the MAP. That would be fine. And if
someone has already done that for you (in this case the manufacturer
who provided the software for approach monitoring) and you're
comfortable that he did the job properly, that's fine too. Use
whatever procedure works for you.

Using the GPS to point at MHT and read DME like that I can understand.
The rest seems awfully like a GPS overlay to the VOR approach, but
this isn't a "VOR or GPS", it's a VOR/DME. Using named waypoints (and
then using the GPS to locate them) makes sense too, but in this case
the MAP isn't a named fix, it's a radial/DME. I guess I'm just making
this more complicated than it needs to be.....

The question become more interesting when GPS is substituted for ADF,
especially when the NDB is the missed approach holding point. One
option (if available) is to use the missed approach sequencing provided
by the GPS for the approach monitoring function (some will even depict
the hold and tell you which entry to use) but anything you care to do,
up to and including setting up the display to read out the bearng and
distance to the NDB and flying the hold off the numbers is acceptable.

If you would tell us more about what kind of equipment you have in the
cockpit, we might be able to make more intelligent suggestions about
what procedures would be optimal.

it's a pretty vanilla stack with an HSI, KLN94, MFD, and dual VOR.

Using the GPS to point at MHT and read DME like that I can
understand.

If that's what it takes to make you feel comfortable, then go with it.

The rest seems awfully like a GPS overlay to the VOR approach

Except it's not. You still have the VOR, not the GPS, driving your HSI
needle, right? That makes it a VOR (or, in this case, VOR/DME)
approach.

Using named waypoints (and
then using the GPS to locate them) makes sense too, but in this case

the MAP isn't a named fix, it's a radial/DME.

So? You could, if you wished, enter it into the GPS and use it. Once
you accept that, is it really a stretch to say that you could also have
someone else enter it?

I guess I'm just making this more complicated than it needs to
be.....

Well, what's happening is that you are confusing the sensor and the
presentation. There is no difference whatsoever in having the GPS give
a distance to MHT vs EGORE vs the MAP of the approach. All of those
waypoints were entered into the database by the manufacturer. You have
no compelling reason to trust one more than another, and the position
is calculated the same way always. It's just a question of how you
want the presentation done, and that's up to you.

Since the KLN94 provides sequencing for approach monitoring, there's
precious little reason not to use it - it gives you a line to follow on
the MFD and a convenient countdown to the next fix. I don't know if
putting the unit in OBS mode will draw a line corresponding to the
selected course on your map - if it will, there is little difference.
If not, that's a compelling reason to use the approach sequencing
instead.

Michael

wrote in message ...
On 11 Feb 2005 11:23:14 -0800, "Michael"
wrote:

I think I'd interpret "as appropriate" as meaning that the GPS
essentially meets the definition of "DME or ADF avionics", since the
rules say it can be substituted for such,

I do not concur, and believe such an interpretation is contrary to the
intent if the statement.

(8) For TSO-C129/129A users, any required alternate airport must still
have
an approved instrument approach procedure other than GPS that is
anticipated
to be operational and available at the estimated time of arrival, and
which
the aircraft is equipped to fly. 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.

I believe the last statement means what it says - that for purposes of
selecting a valid alternate, one must select an approach that can be
completed without reliance on GPS.

Michael


"What it says" depends on how one interprets "as appropriate".

(a) Since it is "appropriate" to substitute GPS for DME and ADF on
non-GPS approaches, then it's acceptable as far as I am concerned.
Furthermore, (b) The aircraft is "equipped to fly" the non-GPS
approach.and (c) they'll never catch me anyway even if I'm wrong.

Well, my 2 cents says that "as appropriate" specifically applies to the phrase "DME or ADF", meaning the
equivalent to the following rewrite: "If the non-GPS approaches on which the pilot must rely require DME, the
aircraft must be equipped with DME; if the non-GPS approaches on which the pilot must rely require ADF , the
aircraft must be equipped with ADF". I agree that other readings are possible, but that's the way I would
normally use and/or hear that idiom.

Cheers,
John Clonts
Temple, Texas
N7NZ

The whole point of all this is to be sure you are not stuck with no
approach because GPS goes dead. Nothing at alternate can require GPS.
That's what it means (I think).

John Clonts wrote:
wrote in message ...

On 11 Feb 2005 11:23:14 -0800, "Michael"
wrote:


I think I'd interpret "as appropriate" as meaning that the GPS
essentially meets the definition of "DME or ADF avionics", since the
rules say it can be substituted for such,

I do not concur, and believe such an interpretation is contrary to the
intent if the statement.


(8) For TSO-C129/129A users, any required alternate airport must still

have

an approved instrument approach procedure other than GPS that is

anticipated

to be operational and available at the estimated time of arrival, and

which

the aircraft is equipped to fly. 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.

I believe the last statement means what it says - that for purposes of
selecting a valid alternate, one must select an approach that can be
completed without reliance on GPS.

Michael


"What it says" depends on how one interprets "as appropriate".

(a) Since it is "appropriate" to substitute GPS for DME and ADF on
non-GPS approaches, then it's acceptable as far as I am concerned.
Furthermore, (b) The aircraft is "equipped to fly" the non-GPS
approach.and (c) they'll never catch me anyway even if I'm wrong.


Well, my 2 cents says that "as appropriate" specifically applies to the phrase "DME or ADF", meaning the
equivalent to the following rewrite: "If the non-GPS approaches on which the pilot must rely require DME, the
aircraft must be equipped with DME; if the non-GPS approaches on which the pilot must rely require ADF , the
aircraft must be equipped with ADF". I agree that other readings are possible, but that's the way I would
normally use and/or hear that idiom.

Cheers,
John Clonts
Temple, Texas
N7NZ

"Bill J" wrote in message
...
The whole point of all this is to be sure you are not stuck with no
approach because GPS goes dead. Nothing at alternate can require GPS.
That's what it means (I think).


I think that is correct, but only for purposes of fuel planning and filing
flight plan.

"Michael" wrote in message
oups.com...

I believe the last statement means what it says - that for purposes of
selecting a valid alternate, one must select an approach that can be
completed without reliance on GPS.

Is a radar approach (presumably requiring no avionics but a Com radio)
authorised for use as an alternate?

Julian Scarfe

On Sat, 12 Feb 2005 09:21:53 GMT, "Julian Scarfe"
wrote:

"Michael" wrote in message
roups.com...

I believe the last statement means what it says - that for purposes of
selecting a valid alternate, one must select an approach that can be
completed without reliance on GPS.

Is a radar approach (presumably requiring no avionics but a Com radio)
authorised for use as an alternate?

Julian Scarfe


Sure. Orlando, Pensacola, Jacksonville all publish alternate minima
for their radar approaches.

Presumably, if no alternate minimums are specified and the airport has
a radar approach, then standard minimums apply.

OK, if my IFR GPS goes out (and my handheld goes out), I am down to
just my VOR/GS. No DME, no ADF, no GPS, no Marker Beacons. Am I legal
to fly an ILS? The only way I have of identifying the outer marker is
ATC radar, so certainly I would need radar coverage. So, lets say I
have radar coverage and its just a plain ILS, no DME or ADF
requirement? Legal? Safe?

On 12 Feb 2005 20:56:18 -0800, "Doug"
wrote:

OK, if my IFR GPS goes out (and my handheld goes out), I am down to
just my VOR/GS. No DME, no ADF, no GPS, no Marker Beacons. Am I legal
to fly an ILS? The only way I have of identifying the outer marker is
ATC radar, so certainly I would need radar coverage. So, lets say I
have radar coverage and its just a plain ILS, no DME or ADF
requirement? Legal? Safe?

I think it would depend on how you identify the missed approach
holding point. If the MHP is an NDB, you have no way of navigating to
it or holding at it. Course, in a radar environment it's unlikely
they'll tell you to go hold as published, but what happens if you have
to go missed and lose comms too?