Intercepting the ILS

JPH wrote:

Can you give an example of how an airspace violation could occur? It
seems that as long as the pilot doesn't descend below the minimum
altitude published for the segment of the approach he's in, then
descending on the glidepath can't put the aircraft any lower than
dropping down immediately to the minimum segment altitude at the
beginning of the segment. If he's in the Intermediate, then the
glidepath will more than likely keep him higher than dropping down to
the minimum altitude due to the length of the intermediate normally
compensating for the required altitude loss at 150 ft per mile optimum.
If the airspace violation would be from the aircraft being too high,
then perhaps the procedure should have a maximum altitude shown or the
controller issue a crossing restriction.

It's happen at LAX quite a few times when the air is hot and the
underlying Ontario airspace rises to provide less than 1,000 feet of
vertical on the LAX G/Ses. The G/S doesn't move.

The glideslope intercept altitude is a minimum altitude, not a mandatory
or maximum altitude. From a TERPS standpoint there's no problem with
descending on the glideslope from 2000 on the procedure in question
instead of 1800.

True enough, and if the pilot wants to remain above the G/S that is
perfectly legal. But, any charted minimum stepdown altitudes prior to
the PFAF are governing, not the G/S.

If the pilot uses the glideslope for backup vertical guidance to give a
smooth transition to the final segment (while using the altimeter
readout outside the FAF to ensure he doesn't descend below 1800) then
what's wrong with that?

Nothing wrong with that.

If the pilot uses the glideslope for backup vertical guidance to give a
smooth transition to the final segment (while using the altimeter
readout outside the FAF to ensure he doesn't descend below 1800) then
what's wrong with that?

Nothing wrong with that.

That isn't really correct either. There's no necessity to monitor
the altimeter at SCK because there's no step-down fixes or other
crossing restrictions at issue. Above 1800 feet on the glideslope, the
glideslope is advisory, but the pilot is perforce satisfying the =1800
foot minimum altitude requirement. Below 1800 feet the glideslope
becomes primary. So in practical terms nothing happens at 1800 feet.
There's nothing to monitor. (OK. I know, you part 121 types have now
reached a point where the weather can below minimums without
necessitating a miss.)

At *Stockton* (the subject of the question), there is no legal issue.
At LAX on the Civet arrival, and other situations where there are
step-down altitudes on the localizer outside the PFAF, there is a
potential issue. The step down minima take precedence over the GS
altitude.

The altitude at the marker is a double check on the
altimeter and the glide slope. If the altimeter is set
incorrectly or broken or if you have intercepted the wrong
glide slope lobe, the pilot has an opportunity to catch the
error and figure out what is wrong.


--
James H. Macklin
ATP,CFI,A&P

--
The people think the Constitution protects their rights;
But government sees it as an obstacle to be overcome.
some support
http://www.usdoj.gov/olc/secondamendment2.htm
See http://www.fija.org/ more about your rights and duties.


wrote in message
oups.com...
| If the pilot uses the glideslope for backup vertical
guidance to give a
| smooth transition to the final segment (while using the
altimeter
| readout outside the FAF to ensure he doesn't descend
below 1800) then
| what's wrong with that?
|
| Nothing wrong with that.
|
| That isn't really correct either. There's no necessity
to monitor
| the altimeter at SCK because there's no step-down fixes or
other
| crossing restrictions at issue. Above 1800 feet on the
glideslope, the
| glideslope is advisory, but the pilot is perforce
satisfying the =1800
| foot minimum altitude requirement. Below 1800 feet the
glideslope
| becomes primary. So in practical terms nothing happens at
1800 feet.
| There's nothing to monitor. (OK. I know, you part 121
types have now
| reached a point where the weather can below minimums
without
| necessitating a miss.)
|
| At *Stockton* (the subject of the question), there is no
legal issue.
| At LAX on the Civet arrival, and other situations where
there are
| step-down altitudes on the localizer outside the PFAF,
there is a
| potential issue. The step down minima take precedence over
the GS
| altitude.
|

The altitude at the marker is a double check on the
altimeter and the glide slope. If the altimeter is set
incorrectly or broken or if you have intercepted the wrong
glide slope lobe, the pilot has an opportunity to catch the
error and figure out what is wrong.

That is of course true - but it's a different altitude, 1758 in this
case. It's the 1800 altiitude that loses significance once the GS has
been intercepted.

BTW, the chances of following the wrong lobe of the GS to the FAF
without noticing a problem is close to nil. It either has reverse
sensing or requires ridiculous rates of descent.

wrote:
If the pilot uses the glideslope for backup vertical guidance to give a
smooth transition to the final segment (while using the altimeter
readout outside the FAF to ensure he doesn't descend below 1800) then
what's wrong with that?


Nothing wrong with that.


That isn't really correct either. There's no necessity to monitor
the altimeter at SCK because there's no step-down fixes or other
crossing restrictions at issue. Above 1800 feet on the glideslope, the
glideslope is advisory, but the pilot is perforce satisfying the =1800
foot minimum altitude requirement. Below 1800 feet the glideslope
becomes primary. So in practical terms nothing happens at 1800 feet.
There's nothing to monitor. (OK. I know, you part 121 types have now
reached a point where the weather can below minimums without
necessitating a miss.)

At *Stockton* (the subject of the question), there is no legal issue.
At LAX on the Civet arrival, and other situations where there are
step-down altitudes on the localizer outside the PFAF, there is a
potential issue. The step down minima take precedence over the GS
altitude.

We are procedurally in violent agreement. Nonetheless, the G/S is not
primary prior to the PFAF, any minimum altitude constraints
notwithstanding. That is the legalese of Part 97. I am just the messenger.

We are procedurally in violent agreement. Nonetheless, the G/S is not
primary prior to the PFAF, any minimum altitude constraints
notwithstanding. That is the legalese of Part 97. I am just the messenger.

We're agreed that at SCK following the glide slope down from the 2000
foot vector altitude is the best procedure. We're also agreed that the
G/S is not primary outside the PFAF. Instead, one must abide by the
published altitudes - in this case we must remain above 1800 until this
PFAF. At SCK, this is logically guaranteed by our "best procedure".

However, I detect that your position is still that some sufficiently
zealous FAA inspector could violate me for using the G/S to descend to
1800. (otherwise how could the new instructor be "technically
correct"?). I disagree. If that is your position, please cite which
verse of Part 97 that this zealous inspector could attempt to violate
me on? Which regulation does our agreed best procedure not comply
with?

It's pointless discussing legality without reference to the law.

wrote:
We are procedurally in violent agreement. Nonetheless, the G/S is not
primary prior to the PFAF, any minimum altitude constraints
notwithstanding. That is the legalese of Part 97. I am just the messenger.


We're agreed that at SCK following the glide slope down from the 2000
foot vector altitude is the best procedure. We're also agreed that the
G/S is not primary outside the PFAF. Instead, one must abide by the
published altitudes - in this case we must remain above 1800 until this
PFAF. At SCK, this is logically guaranteed by our "best procedure".

However, I detect that your position is still that some sufficiently
zealous FAA inspector could violate me for using the G/S to descend to
1800. (otherwise how could the new instructor be "technically
correct"?). I disagree. If that is your position, please cite which
verse of Part 97 that this zealous inspector could attempt to violate
me on? Which regulation does our agreed best procedure not comply
with?

It's pointless discussing legality without reference to the law.

Look at an 8260-3 for any ILS approach. There is probably one or more
on the FAA's coordination web site today. The form is an individual
amendment to Part 97. It sets forth the courses, distances, minimum
altitudes, and location of P-FAF. It can be inferred from the context of
such regulatory document that the G/S is not the primary vertical
guidance mechanism prior to the P-FAF. That is the official view of
those who establish and implement the criteria.

This is reinforced by the fact that the AIM states that the lightening
bolt on NACO ILS charts (profile feather in Jepp charts) consitutes the
beginning of the ILS precision final approach segment. The FAA ILS
criteria for G/S obstacle clearance is not evaluated or used prior to
the PFAF. Intermediate and intial approach segment minimum barometric
altimetry fixes are used to define the vertical component of
intermediate and initial approach segments.

I agree with everything you just wrote. But, you have not addressed
my question. In what way does/can following the glideslope from 2000
to 1800 feet at SCK violate the regulatory implications of the SCK
ILS's 8260-3?

There is no rule that says "thou shalt not follow the G/S unless it
is primary". What the rules say is "thou shall not bust the published
altitude restrictions prior to the PFAF".

Since it isn't logically possible to violate the altitude
restrictions *in this instance* by following the G/S, it can't be
illegal to do so.

The regulatory basis is 91.175(a) which requires "Unless otherwise
authorized by the Administrator, when an instrument letdown to a civil
airport is necessary, each person operating an aircraft, except a
military aircraft of the United States, shall use a standard instrument
approach procedure prescribed for the airport in part 97 of this
chapter."

Part 97 does not prescribe pilot technique. It prescribes the tracks
and altitudes to be flown. If those are complied with, there's no
possible violation.

wrote:
I agree with everything you just wrote. But, you have not addressed
my question. In what way does/can following the glideslope from 2000
to 1800 feet at SCK violate the regulatory implications of the SCK
ILS's 8260-3?

In the specifics cited for Stockton there is no issue of legality. My
understanding was that the CFII in question was making a general
statement about the limitations of the G/S prior to the PFAF; that is,
it is advisory only. Although using it as advisory at Stockton and
using 1800 as the floor prior to the PFAF would be both legal and
permissiable technique, it will not work where there are intervening
stepdown fixes between the point at which the approach clearance is
received and the PFAF.

It is also permissible technique to disregard the G/S and simply drive
it down to 1,800 to intercept the G/S from below, assuming there is
sufficient distance to do that.

I surmised that the CFI was thinking in global terms, and failed to
provide a complete explanation. Then again, my understanding about what
was (in) the CFI's mind is fragile at best.

In general terms: it is not legal to use the G/S as primary prior to the
PFAF. That is an important concept for the pilot to understand. It has
been proven more than once that a lot of air carrier pilots don't
understand it.

What I'm having difficulty reconciling is the following statements of
yours:

"If you can receive the G/S prior to the PFAF, it's only advisory in
any
case, so you are free to use it as you choose, provided you don't
violate any minimum segment altitude or stepdown fixes or any aspect of
an ATC clearance."

I totally agree.

"The new CFI is technically correct but the old CFI is far more
practical."
"In the case cited, the CFI is nitpicking but is nonetheless legally
correct."
"I agree that the CFI is procedurally wrong, although legally correct."


So how can you assert these, *given that in this instance* it is
physically and logically impossible to "violate any minimum segment
altitude or stepdown fixes or any aspect of
an ATC clearance", because
a) the ATC clearance was to maintain 2000 until intercepting the
localizer, and
b) the procedure was to descend on the glide slope to the minimum
segment altitude (1800) at which point the G/S becomes primary.

The point is that blindly following the glideslope has the potential
at places *other than SCK* of causing violations of published
altitudes. Following the G/S is not a violation per se, busting
published or ATC assigned altitudes is.
The CFI is not "technically correct" or "legally correct". What he
could have said, after the flight, is that if one chooses to follow the
G/S prior to the PFAF one needs to be mindful that published and ATC
assigned altitudes have to be complied with, but that at SCK that was
not an issue.