For those of you using handheld GPS's when you fly IFR:

Do you use the throttle to increase/decrease power to match the ground
speed to the approach speed table so the time is correct to the MAP?

Or,

Do you use the distance to the airport to determine/verify the MAP, even
though the time may not have expired?

No

Dave

john smith wrote:

> For those of you using handheld GPS's when you fly IFR:
>
> Do you use the throttle to increase/decrease power to match the ground
> speed to the approach speed table so the time is correct to the MAP?
>
> Or,
>
> Do you use the distance to the airport to determine/verify the MAP, even
> though the time may not have expired?
>

john smith wrote:

> For those of you using handheld GPS's when you fly IFR:
>
> Do you use the throttle to increase/decrease power to match the ground
> speed to the approach speed table so the time is correct to the MAP?

A buddy of mine does this. Drives me nuts. He'll sit and screw with
the throttle to get 90 knots ground speed. I want to reach over there
and smack him upside the head. He makes himself so busy trying to fly a
certain groundspeed and he can't see that.

On 9/7/04 6:50 AM, john smith wrote the following:

> For those of you using handheld GPS's when you fly IFR:
>
> Do you use the throttle to increase/decrease power to match the ground
> speed to the approach speed table so the time is correct to the MAP?
>
> Or,
>
> Do you use the distance to the airport to determine/verify the MAP, even
> though the time may not have expired?
>

Either activity seems unnecessary to this relatively new IA pilot.
Maybe because I already have enough to do on an approach.

Option 1 also sounds like a good way to get dangerously slow if you have
a stiff tailwind.

Doesn't seem like the MAP is that important. So what if you are a bit
early or late when you decide you can't see where you're going? The
result is the same, or should be.

john smith > wrote in news:Cgh%c.81922$cT6.12543
@fe2.columbus.rr.com:

> For those of you using handheld GPS's when you fly IFR:
>
> Do you use the throttle to increase/decrease power to match the ground
> speed to the approach speed table so the time is correct to the MAP?
>
> Or,
>
> Do you use the distance to the airport to determine/verify the MAP, even
> though the time may not have expired?
>

The MAP time is an indirect way to measure distance. If you can measure
distance directly, why would you still choose the indirect method?

Of course, since the handheld is not an IFR approved device, you will have
to exercise some caution during approaches. What I would recommend is, do
the timing as if you didn't have the GPS, and then verify that it agrees
with the MAP shown on the GPS when the clock winds down to zero.

"Andrew Sarangan" > wrote in message
. 158...
> john smith > wrote in news:Cgh%c.81922$cT6.12543
> @fe2.columbus.rr.com:
>
> > For those of you using handheld GPS's when you fly IFR:
> >
> > Do you use the throttle to increase/decrease power to match the ground
> > speed to the approach speed table so the time is correct to the MAP?

I really, really, really would recommend flying an airspeed under all
circumstances.

> > Do you use the distance to the airport to determine/verify the MAP, even
> > though the time may not have expired?

Legally your IFR approved clock for timed approaches and NDB for NDB
approaches are what you WILL use. Rationally if my clock or NDB disagreed
with my GPS and I had to make a choice I would trust the GPS.

Along the same GPS train of thought. Try (under VFR with safety pilot)
flying partial panel using "wet" compass and then fly same maneuvers using
the "pseudo" panel on your GPS. Which is easier? Which is more accurate?

I can understand the FAA wanting to avoid a free for all by regulating GPS
usage so carefully. But each pilot, if faced with conflicting data, needs to
decide which technology they trust their life to. The best way to do that is
lots of practice under VFR checking clock vs. GPS, NDB vs. GPS, VOR vs. GPS,
Localizer vs. GPS and make up your own mind.

Also if you are not a renter you might consider spending 15-20K for an IFR
certified GPS linked to your autopilot.

Cheers
Howard
C182P




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Mitty > writes:

> [...] Doesn't seem like the MAP is that important. So what if you
> are a bit early or late when you decide you can't see where you're
> going? The result is the same, or should be.

Depending on how big "a bit" is, being late to "go missed" can put one
outside the airspace protected from obstructions.

- FChE

On 9/7/04 1:21 PM, Frank Ch. Eigler wrote the following:

> Mitty > writes:
>
>
>>[...] Doesn't seem like the MAP is that important. So what if you
>>are a bit early or late when you decide you can't see where you're
>>going? The result is the same, or should be.
>
>
> Depending on how big "a bit" is, being late to "go missed" can put one
> outside the airspace protected from obstructions.
>
> - FChE

Point taken, but you can do rough math within "a bit" in your head I
think. Particularly with a ground speed readout on the GPS. Or
interpolate off the plate.

john smith > wrote
> For those of you using handheld GPS's when you fly IFR:
>
> Do you use the throttle to increase/decrease power to match the ground
> speed to the approach speed table so the time is correct to the MAP?

Absoutely not. It's a moronic way to do things. Only the Airbus
flight control system does anything of the sort.

> Do you use the distance to the airport to determine/verify the MAP, even
> though the time may not have expired?

I use the GPS to 'estimate' the winds and compute ground speed.
Because of this, my timing to the missed approach point is always
perfect :).

Michael

Mitty wrote:
> Doesn't seem like the MAP is that important.

On an instrument approach, it's the most important thing in the world.

> So what if you are a bit
> early or late when you decide you can't see where you're going?

You'd better study this a bit, because if you manage to get through
your IFR checkride without busting it a bit, this attitude may soon
make you dead a bit.

On 9/7/04 4:02 PM, Brien K. Meehan wrote the following:

> Mitty wrote:
>
>>Doesn't seem like the MAP is that important.
>
>
> On an instrument approach, it's the most important thing in the world.
>
>
>>So what if you are a bit
>>early or late when you decide you can't see where you're going?
>
>
> You'd better study this a bit, because if you manage to get through
> your IFR checkride without busting it a bit, this attitude may soon
> make you dead a bit.
>

I don't want to turn this into a flame war, but I'll take the bait here:

How (calculator, flight computer, mentally, etc.) and how precisely,
during an approach, do you calculate your time to the MAP based on your
ground speed crossing the FAF? Finally, to you, what is an acceptable
"bit?"

My checkride went fine, thanks.

Mitty > wrote:
> How (calculator, flight computer, mentally, etc.) and how precisely,
> during an approach, do you calculate your time to the MAP based on your
> ground speed crossing the FAF? Finally, to you, what is an acceptable
> "bit?"

A perfectly reasonable question. Lacking any better instrumentation
(DME, or GPS), here's what I do:

1) Estimate the surface wind based on the best information you've got
(which usually means ATIS or AWOS).

2) Add some random fudge factor to account for the fact that the winds
at 500 - 2000 AGL (where you're going to be flying the approach) will
tend to be a bit stronger than on the surface.

3) If it's not a direct head or tail wind, take a WAG at the
head/tailwind component.

4) Add this to the indicated airspeed you plan on flying the approach at
(at the speeds and altitudes you usually use for approaches, IAS is
close enough to TAS that you shouldn't worry about the difference).

5) You now have a reasonable estimate of your groundspeed. If you're
trying to refine this estimate to anything closer than the nearest 10
kts, you're fooling yourself.

6) Now, look at the FAF-to-MAP timing table and do a rough interpolation
between the listed entries.

If you spend more than about 30 seconds on the whole process, you're
working too hard. Without a reliable way to measure GS, the best you
can do is a reasonable guess, so don't knock yourself out trying to do
anything fancier.

With a handheld GPS, you're be insane not to take advantage of the
information it gives you. If the MAP itself is not in the database, set
it navigating to the ARP, or the FAF, or the last stepdown fix, or
whatever makes the most sense for that approach. Start your watch to be
legal, but use your GPS to be safe.

> A buddy of mine does this. Drives me nuts. He'll sit and screw with
> the throttle to get 90 knots ground speed. I want to reach over there
> and smack him upside the head. He makes himself so busy trying to fly a
> certain groundspeed and he can't see that.

does your friend fly a groundspeed or fly the plane? I know the plane
flies through the air and doesn't know which way the ground goes
(up/down/left/right/forward/backward). If he is doing an
circle-to-land approach say in a 152 with 50 knot tail wind, does
he really have a IAS of 20 knots (or whatever a 152 does an approach
at). If so, his ground speed might be zero knots when he stalls.

Gerald

On 9/7/04 6:21 PM, Roy Smith wrote the following:

> Mitty > wrote:
>
>>How (calculator, flight computer, mentally, etc.) and how precisely,
>>during an approach, do you calculate your time to the MAP based on your
>>ground speed crossing the FAF? Finally, to you, what is an acceptable
>>"bit?"
>
>
> A perfectly reasonable question. Lacking any better instrumentation
> (DME, or GPS), here's what I do:
>
> 1) Estimate the surface wind based on the best information you've got
> (which usually means ATIS or AWOS).
>
> 2) Add some random fudge factor to account for the fact that the winds
> at 500 - 2000 AGL (where you're going to be flying the approach) will
> tend to be a bit stronger than on the surface.
>
> 3) If it's not a direct head or tail wind, take a WAG at the
> head/tailwind component.
>
> 4) Add this to the indicated airspeed you plan on flying the approach at
> (at the speeds and altitudes you usually use for approaches, IAS is
> close enough to TAS that you shouldn't worry about the difference).
>
> 5) You now have a reasonable estimate of your groundspeed. If you're
> trying to refine this estimate to anything closer than the nearest 10
> kts, you're fooling yourself.
>
> 6) Now, look at the FAF-to-MAP timing table and do a rough interpolation
> between the listed entries.
>
> If you spend more than about 30 seconds on the whole process, you're
> working too hard. Without a reliable way to measure GS, the best you
> can do is a reasonable guess, so don't knock yourself out trying to do
> anything fancier.
>

OK, that's basically what I do too and the consequent errors are what I
meant by the "a bit" comment that led to Meehan's smart-ass shot. "A
bit" is maybe a 10-15% error on the time sans. I have no interest in
studying the TERPS design rules but I gotta believe that they leave us
plenty safe with that size error.

> With a handheld GPS, you're be insane not to take advantage of the
> information it gives you. If the MAP itself is not in the database, set
> it navigating to the ARP, or the FAF, or the last stepdown fix, or
> whatever makes the most sense for that approach. Start your watch to be
> legal, but use your GPS to be safe.

No argument. But the original poster's idea sounded like head-down
during an approach managing airspeed as it gets updated on a GPS -- that
idea still scares me. I'm not smart enough to fly an approach while
trying to do that, too. & I think it's unnecessary.

"Howard Nelson" > wrote in message >...

> I really, really, really would recommend flying an airspeed under all
> circumstances.

Ditto. Planes fly airspeed, not groundspeed. I was taught to fly
standard configurations of pitch, power, and trim. These should
produce known airspeeds which set the plane up well for the specific
phase of flight.

> > > Do you use the distance to the airport to determine/verify the MAP, even
> > > though the time may not have expired?
>
> Legally your IFR approved clock for timed approaches and NDB for NDB
> approaches are what you WILL use. Rationally if my clock or NDB disagreed
> with my GPS and I had to make a choice I would trust the GPS.

The conservative choice would be to listen to the first box that cries
"miss." Let's say the wind shifts and your groundspeed changes, the
handheld says you're there. Might be good to miss it. If OTOH the
clock says you're there and the GPS doesn't, you're not going to
increase your risks by missing on that basis.

> I can understand the FAA wanting to avoid a free for all by regulating GPS
> usage so carefully. But each pilot, if faced with conflicting data, needs to
> decide which technology they trust their life to. The best way to do that is
> lots of practice under VFR checking clock vs. GPS, NDB vs. GPS, VOR vs. GPS,
> Localizer vs. GPS and make up your own mind.

I use handheld GPS and panel Loran to cross-check everything else in
my non GPS-equipped C-172.

Like you say, there's no way the FAA will ever allow handheld GPS as
an official navigational device for IFR, but they've also made a wise
decision to not prevent it from being used anyway. A Decent handheld
GPS and COM radio give a pilot a fighting chance to get down through
the clouds in a total electrical failure, which is one of the
emergencies I worry about most in a middle-aged plane like mine. (NB-
I have a Precise Flight standby vacuum already)

> Also if you are not a renter you might consider spending 15-20K for an IFR
> certified GPS linked to your autopilot.

You could probably put a good used box in for a lot less, though
perhaps not linked to the A/P. 6K range for a used King/Apollo unit +
install/certification is the estimate I've seen from multiple sources
for a 172.

Mitty > wrote:
> No argument. But the original poster's idea sounded like head-down
> during an approach managing airspeed as it gets updated on a GPS -- that
> idea still scares me.

And it should. Fly whatever airspeed you're used to flying
non-precision approaches at (90 KIAS is typical for common trainer
types). The instrument to watch for managing airspeed is the ASI. Your
groundspeed is whatever it works out to be.

(C Kingsbury) wrote:
> The conservative choice would be to listen to the first box that cries
> "miss." Let's say the wind shifts and your groundspeed changes, the
> handheld says you're there. Might be good to miss it. If OTOH the
> clock says you're there and the GPS doesn't, you're not going to
> increase your risks by missing on that basis.

I don't know if I agree with that. Let's say your calculations are
wrong and the timer runs out when you're 1/2 mile from the MAP. Which
has less overall risk:

1) Continuing another 1/2 mile to the real geographic MAP based on your
GPS, finding the runway, and landing uneventfully.

2) Going missed, and being back in the clouds trying to decide if you
should try the approach again or divert.

#1 sure sounds safer to me.

<<Do you use the throttle to increase/decrease power to match the
ground speed to the approach speed table so the time is correct to the
MAP?>>

I find this concept astonishing. Surely very, very few CFII's are
teaching this? I have run into one or two.

You use the time appropriate to the ground speed you have, when flying
an appropriate indicated airspeed.

Newps > wrote in message >...
> john smith wrote:
>
> > For those of you using handheld GPS's when you fly IFR:
> >
> > Do you use the throttle to increase/decrease power to match the ground
> > speed to the approach speed table so the time is correct to the MAP?
>
> A buddy of mine does this. Drives me nuts. He'll sit and screw with
> the throttle to get 90 knots ground speed.

*** Even with a brisk tailwind?

- Jerry Kaidor ( )

> You could probably put a good used box in for a lot less, though
> perhaps not linked to the A/P. 6K range for a used King/Apollo unit +
> install/certification is the estimate I've seen from multiple sources
> for a 172.

Yep. It's that install/linking/cert that runs the price up. Other than a
430/530 box the labor may well equal the price of the unit.

Howard


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Howard Nelson wrote:


>
>
> Legally your IFR approved clock for timed approaches and NDB for NDB
> approaches are what you WILL use.

Legally I will use the IFR approved GPS and the little mileage number on
the plate. Screw the timing.

"Newps" > wrote in message
...
>
>
> Howard Nelson wrote:
>
>
> >
> >
> > Legally your IFR approved clock for timed approaches and NDB for NDB
> > approaches are what you WILL use.
>
> Legally I will use the IFR approved GPS and the little mileage number on
> the plate. Screw the timing.

Here I thought we were discussing portable GPS's. My bad.

Howard
>


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Fly the same airspeed and final approach configuration all the time. Legally
you need to interpolate the table and estimate a time to MAP. Also
very handy should the GPS take a dump during final approach.

Realistically .. look at the GPS distance to the airport when you cross
the final approach fix. Subtract the distance to the MAP
and when the GPS says you're there .. go missed if you don't
have the runway.

Don't make it any harder than it needs to be. To me jockeying with
airspeed using a GPS to match a 90k ground speed is kind of silly
when the GPS will tell you right when you're at MAP.




"john smith" > wrote in message
...
> For those of you using handheld GPS's when you fly IFR:
>
> Do you use the throttle to increase/decrease power to match the ground
> speed to the approach speed table so the time is correct to the MAP?
>
> Or,
>
> Do you use the distance to the airport to determine/verify the MAP, even
> though the time may not have expired?
>

Mitty > wrote
> OK, that's basically what I do too and the consequent errors are what I
> meant by the "a bit" comment that led to Meehan's smart-ass shot. "A
> bit" is maybe a 10-15% error on the time sans. I have no interest in
> studying the TERPS design rules but I gotta believe that they leave us
> plenty safe with that size error.

Don't bet on it. Study the rules.

I used to believe that just because you flew a VOR approach to well
within instrument PTS standards, using a VOR that had easily passed,
and would easily pass again, a VOR check, that I could be assured of
not slamming into an obstruction if I was still 200 ft above the MDA.
WRONG.

Michael

Roy Smith > wrote in message >...
> (C Kingsbury) wrote:
> > The conservative choice would be to listen to the first box that cries
> > "miss." <snip>

>
> I don't know if I agree with that. Let's say your calculations are
> wrong and the timer runs out when you're 1/2 mile from the MAP. Which
> has less overall risk:
>
> 1) Continuing another 1/2 mile to the real geographic MAP based on your
> GPS, finding the runway, and landing uneventfully.
>
> 2) Going missed, and being back in the clouds trying to decide if you
> should try the approach again or divert.
>
> #1 sure sounds safer to me.

You're begging the question: "If I listen to the GPS and land safely,
isn't it safer to listen to the GPS and not head back up into the
clouds?" Of course it is, but you don't know in advance that following
the GPS will lead you to a safe landing. Check out this approach:

http://204.108.4.16/d-tpp/0409/00654VG23.PDF (VOR-23 @ LWM on Airnav)

Stright-in this will bring you down into a real minefield of stacks
and towers. Now let's say on the way down you plan to dial the VOR
into the GPS to get a DME reading to use as the MAP. But in the heat
of the moment you put LWM the airport instead of LWM the VOR in. This
means you'll wait until you're past the airport to miss. You're
probably OK so long as you don't go down any further, but you've
unquestionably increased your risk.

Or perhaps you're used to an approach at your home field where the DME
counts down, instead of up. You get distracted and see 3DME here, and
think, OK, I have 1.5 to go. So you putter on until you're 5 miles
away. Right about where that 606' obstacle is. Downdraft anyone?

My situation is purely hypothetical, but not at all unrealistic. I've
made every one of these mistakes in isolation. Even if I used the GPS
as a primary means of determining MAP, I would back it up with the
timer, which would quickly catch the gross errors described above.

Second, your response assumes that diverting to the alternate actually
increases risk. This is a variable situation. Where I fly in the
Northeast, you usually don't have to go more than 20-30 miles to find
an airport serviced by an ILS, which is usually what you'll put in as
an alternate if you're headed to a field with no precision approaches.
If your alternate is an asphalt patch with an NDB on the field, well,
then maybe you're better off trying to limbo your way in.

Best,
-cwk.

In article >,
(C Kingsbury) wrote:

> You're begging the question: "If I listen to the GPS and land safely,
> isn't it safer to listen to the GPS and not head back up into the
> clouds?" Of course it is, but you don't know in advance that following
> the GPS will lead you to a safe landing. Check out this approach:
>
> http://204.108.4.16/d-tpp/0409/00654VG23.PDF (VOR-23 @ LWM on Airnav)
>
> Stright-in this will bring you down into a real minefield of stacks
> and towers.

All of which are below the MDA. Which is a good reason not to descend
below the MDA unless you have the runway in sight.

> Now let's say on the way down you plan to dial the VOR
> into the GPS to get a DME reading to use as the MAP. But in the heat
> of the moment you put LWM the airport instead of LWM the VOR in. This
> means you'll wait until you're past the airport to miss. You're
> probably OK so long as you don't go down any further, but you've
> unquestionably increased your risk.

You can always screw up. That's why you brief approach procedures and
double-check your setup. What if you calculated the FAF-MAP time as
3:10, but put 4:10 into the clock instead?

I'm still going to believe a handheld GPS is more accurate than a DR
track. It may not be legal, but it's common sense.

Keep in mind that starting the missed too early can be as bad as turning
too late, it the procedure involves a turn predicated on you already
being past an obstacle.

Greg Esres > wrote
> <<Do you use the throttle to increase/decrease power to match the
> ground speed to the approach speed table so the time is correct to the
> MAP?>>
>
> I find this concept astonishing. Surely very, very few CFII's are
> teaching this? I have run into one or two.

It will be more popular. Watch and see.

This method is used by the flight control software of the Airbus A-320
series of aircraft. I **** you not. Straight from the lips of an
A-320 captain. The autothrottles adjust to a given groundspeed on
approach. Groundspeed, not airspeed. No, I don't know why either -
but he insists that it's true.

Once more aiplanes adopt this approach, I am willing to bet it will
become the norm at the big flight schools - especially as IFR GPS
becomes standard. And once the big flight schools start teaching
it...

Michael

Roy Smith wrote:
> In article >,
> (C Kingsbury) wrote:
>
>
>>You're begging the question: "If I listen to the GPS and land safely,
>>isn't it safer to listen to the GPS and not head back up into the
>>clouds?" Of course it is, but you don't know in advance that following
>>the GPS will lead you to a safe landing. Check out this approach:
>>
>>http://204.108.4.16/d-tpp/0409/00654VG23.PDF (VOR-23 @ LWM on Airnav)
>>
>>Stright-in this will bring you down into a real minefield of stacks
>>and towers.
>
>
> All of which are below the MDA. Which is a good reason not to descend
> below the MDA unless you have the runway in sight.
>
>
>>Now let's say on the way down you plan to dial the VOR
>>into the GPS to get a DME reading to use as the MAP. But in the heat
>>of the moment you put LWM the airport instead of LWM the VOR in. This
>>means you'll wait until you're past the airport to miss. You're
>>probably OK so long as you don't go down any further, but you've
>>unquestionably increased your risk.
>
>
> You can always screw up. That's why you brief approach procedures and
> double-check your setup. What if you calculated the FAF-MAP time as
> 3:10, but put 4:10 into the clock instead?
>
> I'm still going to believe a handheld GPS is more accurate than a DR
> track. It may not be legal, but it's common sense.
>
> Keep in mind that starting the missed too early can be as bad as turning
> too late, it the procedure involves a turn predicated on you already
> being past an obstacle.

Maybe someone can tell us how a hand-held GPS behaves with lots of
moisture in the air? I've been doing a lot of geocaching recently and
know for sure that trees cause outages. Maybe aircraft-certified GPS
units get around this somehow or at least flag the unreliable situation.
But how do you fly if you can't trust the GPS?

"William W. Plummer" > wrote:
> Maybe someone can tell us how a hand-held GPS behaves with lots of
> moisture in the air? I've been doing a lot of geocaching recently and
> know for sure that trees cause outages. Maybe aircraft-certified GPS
> units get around this somehow or at least flag the unreliable situation.
> But how do you fly if you can't trust the GPS?

Trees block the frequencies that GPS uses. Rain and water vapor doesn't.

Presumably, if you're using the GPS for an instrument approach, you're
above treetop level, so the leaves shouldn't be blocking the signal :-)

It is certainly true that IFR certified GPS's detect and alert on
unreliable signals (that's what RAIM is all about). I still think a
handheld GPS is more accurate and reliable than a stopwatch.

john smith > wrote in message >...
> For those of you using handheld GPS's when you fly IFR:
>
> Do you use the throttle to increase/decrease power to match the ground
> speed to the approach speed table so the time is correct to the MAP?
>
> Or,
>
> Do you use the distance to the airport to determine/verify the MAP, even
> though the time may not have expired?

Fly the same airspeed as always, measure the groundspeed from the GPS,
and interpolate the timing table for your ground speed.

One thing to remember is that the MAP does not have to be over the
airport. It may be a few miles before the runway, or past the runway.
This is a concern even when using an approach certified GPS because
the MAP may not be in the database. An example would be a MAP that is
a DME fix off a localizer. Most GPS databases do not contain the
lat/lon for localizer stations.

(Michael) wrote

> This method is used by the flight control software of the Airbus A-320
> series of aircraft. I **** you not. Straight from the lips of an
> A-320 captain. The autothrottles adjust to a given groundspeed on
> approach. Groundspeed, not airspeed. No, I don't know why either -
> but he insists that it's true.

Well...I have a pretty good idea why without ever having been
in an Airbus. MicroBurst. On an ILS using a "normal" autopilot
and autothrottles, when approaching a microburst, the autothrottles
(or human pilot) will retard the throttles to maintain Glideslope
and IAS and then shortly after passing the microburst, one finds
himself with reduced power and rapidly reducing airspeed. Been
there--Done that!
By flying a groundspeed that is proportional to the strength of the
microburst on the front side of the microburst, one just might survive
the backside. Without the Groundspeed input, one just adds some
arbitrarily chosen number of knots to the IAS, wanting at the same
time to keep it as low a number as possible because you had to get
rid of any excess prior to touchdown.
In really bad conditions, indicated by a larger than normal difference
between IAS and GS, I always kept the GS up.

Bob Moore
ATP B-727 B-707
PanAm (retired)

Andrew Sarangan wrote:

> Most GPS databases do not contain the
> lat/lon for localizer stations.

Not sure about most. Many do.

"Andrew Sarangan" > wrote in message
om...
>
> Fly the same airspeed as always, measure the groundspeed from the GPS,
> and interpolate the timing table for your ground speed.
>

If you trust the GPS to provide accurate groundspeed why not trust it to
determine the MAP?

On Tue, 07 Sep 2004 11:50:58 GMT, john smith > wrote:

>For those of you using handheld GPS's when you fly IFR:
>
>Do you use the throttle to increase/decrease power to match the ground
>speed to the approach speed table so the time is correct to the MAP?

No sir. That could, or is a very dangerous practice.
You compute the time to the MAP based on the Gs while flying your
normal airspeed on approach.

>
>Or,
>
>Do you use the distance to the airport to determine/verify the MAP, even
>though the time may not have expired?

I use it along with the RNAV computer to give time and distance for
situational awareness.

If I did everything right the time expires when I reach the MAP (or
close to it)

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

This is not scientific in any way, but judging from the maps I have made
overlaying my GPS track on geo-referenced satellite images (using
USAPhotoMaps and TerraServer), it is extremely accurate. This track data
was made using my Garmin 196, I think WAAS was active at the time (although
it was before the official rollout).

http://home.comcast.net/~jslew/Photomap2m.png

"Jeremy Lew" > wrote in message >...

> This is not scientific in any way, but judging from the maps I have made
> overlaying my GPS track on geo-referenced satellite images (using
> USAPhotoMaps and TerraServer), it is extremely accurate. This track data
> was made using my Garmin 196, I think WAAS was active at the time (although
> it was before the official rollout).
>
> http://home.comcast.net/~jslew/Photomap2m.png

Looks like you're flying one of ECAC's Warriors? Pretty impressive.

Kind of reminds me of bringing my father's sailboat up the Connecticut
River in 1/4mi viz. fog. He has DGPS and radar, and at slack tide, if
you navigated straight to where the GPS said the buoy would be, you'd
probably hit it. Accuracy was close to that provided by the radar set,
and a lot easier to read. Of course the GPS can't tell you where the
other boats are...

Everyone agrees GPS, even if "just a handheld," is probably the most
accurate navigational system onboard. It's all a question of how far
you carry that. Me, I prefer to split differences wherever possible.
Anything to increase the odds of catching a really bad error before
it's too late.

Best,
-cwk.

"C Kingsbury" > wrote in message
m...
> "Jeremy Lew" > wrote in message
>...
>
> Looks like you're flying one of ECAC's Warriors? Pretty impressive.

Colin, good eye, but you obviously need some practice distinguishing Katana
GPS tracks from Warrior GPS tracks ;) Actually, there's tracks from several
flights there, so it's probably a mix of both types.