FAR Part 97: Aircraft Approach Categories - IAS vs Ground Speed

Yes he did.

No he didn't.

Say, is this the five minute argument, or did you want the full half hour?

Jose
--
Nothing takes longer than a shortcut.
for Email, make the obvious change in the address.

"Jose" wrote in message
news

No he didn't.


Of course he did.



Say, is this the five minute argument, or did you want the full half hour?


This isn't an argument at all.

"Steven P. McNicoll" writes:
"Jose" wrote

No he didn't.

Of course he did.

Say, is this the five minute argument, or did you want the full half hour?

This isn't an argument at all.

And with no context, the casual reader has no idea
what the quibbling is about...

wrote in message ...
Gary Drescher wrote:
wrote in message
...
"Steven P. McNicoll" wrote:

wrote in message
...
You are correct. There is no end to what some flight
instructors will dream up or invent. Everything the FAA
does in the world of charting is predicated on IAS.

Not quite everything. The approach timing table uses ground speed.

More correctly, the Jeppesen timing table states ground speed.
NACO does not.

Whether they state it or not, there's nothing but ground speed that they
*could* be using to calculate the time to traverse the stated distance.

For the best accuracy, it obviously has to be ground speed. But, there is
no
requirement to make the necessary calculations to arrive at ground speed.
A
lot of folks over many years have simply treated the timing table values
as
indicated airspace,

Whatever shortcuts pilots may take, the fact remains that the NACO timing
tables do use GS, just as the Jepp tables do. If wind is negligible and CAS
is close to IAS, then of course IAS closely approximates GS, but it's still
GS that's given in the tables.

on the premise there are a lot more important things to do
in the final approach segment than attempt to make conversions.

But why would you wait until the final approach segment to make the
conversion? I consider it part of the approach-briefing to calculate GS from
IAS and reported wind, and to write down the appropriate time to the MAP.

In recent years, RNAV has all-but-eliminated any need to use the timing
table
in any case.

Even if your RNAV is certified for IFR, I think it's still a good idea to
pre-compute your time to the MAP in case your RNAV fails during the
approach.

--Gary

"Gary Drescher" wrote in message
...
Whatever shortcuts pilots may take, the fact remains that the NACO timing
tables do use GS, just as the Jepp tables do. If wind is negligible and
CAS is close to IAS, then of course IAS closely approximates GS,

Only for sea level airports. You will be off by about 20% landing at a
6000msl airport.


but it's still GS that's given in the tables.

"Harlo Peterson" wrote in message
...
"Gary Drescher" wrote in message
...
Whatever shortcuts pilots may take, the fact remains that the NACO timing
tables do use GS, just as the Jepp tables do. If wind is negligible and
CAS is close to IAS, then of course IAS closely approximates GS,

Only for sea level airports. You will be off by about 20% landing at a
6000msl airport.

Yup, density altitude is a factor too; my flatlander assumptions were
showing. But even at 6000', the discrepancy is less than 10%, not 20%.
Still, you're right that the discrepancy is large enough to matter.

--Gary

"Gary Drescher" wrote in
:

Yup, density altitude is a factor too; my flatlander assumptions were
showing. But even at 6000', the discrepancy is less than 10%, not
20%. Still, you're right that the discrepancy is large enough to
matter.

Not to mention that your assumed GS for the approach will only be a WAG
anyway. The winds on the approach can be greatly different from the
winds at your cruise altitude, and from the reported surface winds.
TERPS gives you enough protection so that it really doesn't matter much
anyway. Using the ARP or the runway in the GPS for the MAP will be much
more precise than timing anyway.

--
Regards,

Stan

"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin

Roy Smith wrote:

wrote:
And, your reference that the speeds on NACO charts are ground speeds?

Oh, come on, this is getting silly. The table is labeled (for example, on
the HPN NDB 16) "FAF to MAP 4.8 NM". That's one point on the ground to
another point on the ground. The times in the table tell you how long it
will take to cover that distance at various speeds. What else could the
speeds possibly mean if not ground speed?

Most everything pertaining to instrument procedures is predicated on fixes,
facilities or waypoints either on the ground or geo-referenced to a precise
location on the ground. Yet, many (most) of these procedures are predicated on
indicated airspeed.

The origin of the timing table was not specifically referenced to ground
speed. In fact, the KISS concept in pre-GPS days favored simply applying IAS
on final, as in managing human factors and keeping the priority tasks at the
top of the list, so to speak. So, the discussion is not silly at all.

wrote:

Most everything pertaining to instrument procedures is predicated on fixes,
facilities or waypoints either on the ground or geo-referenced to a precise
location on the ground. Yet, many (most) of these procedures are predicated on
indicated airspeed.

The origin of the timing table was not specifically referenced to ground
speed. In fact, the KISS concept in pre-GPS days favored simply applying IAS
on final, as in managing human factors and keeping the priority tasks at the
top of the list, so to speak. So, the discussion is not silly at all.

Well, I don't get it. Sure seems silly to me, too. Would you mind explaining the
arithmetic operations involved in calculating the airspeeds that you claim go
into the table? What are the data from which you begin, and what operations do
you perform on those data to derive airspeed?

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Mike,
Actually, niether Vbg nor minimum sink is correct in all circumstances. Vbg
will yield the greatest distance by definition, and minimum sink will yield
the greatest time. Which one is the most beneficial? Gotta look at the
circumstances. There is a good discussion at
http://www.auf.asn.au/emergencies/aircraft.html#vbg
Dan Malcolm

"Mike Rapoport" wrote in message
ink.net...
I had a primary instructor who insisted that the best speed to use in the
event of an engine failure was the published best glide speed. I said that
it must depend on the wind and pointed out that if there was a headwind
equal to Vbg that any speed over the Vbg was better. I also pointed out
that with a strong tailwind that the minimium sink speed would get more
distance. He continued to insist that Vbg was the speed to use. That was
our last flight.

We all harbor misconceptions but there is no excuse for being too stubborn
to learn.

Mike
MU-2

"Mark Hansen" wrote in message
...
On 7/15/2005 12:12, Mike Rapoport wrote:

"Mark Hansen" wrote in message
...
On 7/15/2005 11:52, Steven P. McNicoll wrote:

"Mark Hansen" wrote in message
...

No, Actually, he's not (unfortunately).


Well, he had to get the idea they were ground speeds somewhere. The
timing table is pretty much the only possible source.

His reasoning is that the faster we're moving across the ground,
the faster we'll move outside of the protected area, for example,
on the circling maneuver, and that to use the higher minimums
'just made good common sense'.

However, he's interpreting the rule using this 'common sense'
and claiming that this is what the rule implies.

He made it clear to me that he was talking about the approach category
minimums and not just the time from FAF to MAP (which, of course,
is based on ground speed).



--
Mark Hansen, PP-ASEL, Instrument Student
Sacramento, CA

This CFII is stupid. Once you start circling the winds change and will
become a headwind at some point.

Ya know ... I mentioned this to him as well. However, I think he's
stuck on the Ground Speed reported by the GPS during the final
approach as being the speed used to determine the approach category...
That's just not what the FARs say.


Mike
MU-2


--
Mark Hansen, PP-ASEL, Instrument Student
Sacramento, CA