Commencing a GPS approach from a fix other than the FAF

"Sam Spade" wrote in message
...
Roy Smith wrote:


It ATC is allowed to send you direct to an IF, then the distinction
between IF and IAF has, for all practical matters, been eliminated. If
that's the case, then the databases and/or software needs to be updated
to have the IFs show up in the menu.

It will take quite a few years for the FAA to identify all the IFs.
Direct-to-the IF is not an "if" for RNAV IAPs. ;-)

It's been in the AIM and 7110.65 for about a year now.

What's to identify? If it is not an IAF, and not the FAF, and is on an
intermediate segment, it is an IF. Why does it need to be "identified"?

PCG:

INTERMEDIATE FIX- The fix that identifies the beginning of the intermediate
approach segment of an instrument approach procedure. The fix is not
normally identified on the instrument approach chart as an intermediate fix
(IF).

Intermediate Approach- The segment between the intermediate fix or point and
the final approach fix.

(Is that circular, or what?)

Stan Prevost wrote:
"Sam Spade" wrote in message
...

Roy Smith wrote:


It ATC is allowed to send you direct to an IF, then the distinction
between IF and IAF has, for all practical matters, been eliminated. If
that's the case, then the databases and/or software needs to be updated
to have the IFs show up in the menu.

It will take quite a few years for the FAA to identify all the IFs.
Direct-to-the IF is not an "if" for RNAV IAPs. ;-)

It's been in the AIM and 7110.65 for about a year now.


What's to identify? If it is not an IAF, and not the FAF, and is on an
intermediate segment, it is an IF. Why does it need to be "identified"?

Because sometimes there is a stepdown fix, or two, in the initial
segment, and sometimes there is a stepdown fix, or two, in the
intermediate segment. In that event you do not know which fix is the
intermediate fix (well, we're really speaking of waypoints since this is
an RNAV-only procedure).

If there is only one fix between the IAF and the FAF that, indeed, is
the IF. You are free to determine that on a ad hoc basis as are
controllers.

Jeppesen and NACO, are not. They will not designate the IF until it
appears on the official source. The database vendors, if they chose to
designate IFs in the database, would also not do it on an ad hoc basis.

That's the way the procedures and charting systems work.

"Sam Spade" wrote in message
...
Stan Prevost wrote:
"Sam Spade" wrote in message
...



What's to identify? If it is not an IAF, and not the FAF, and is on an
intermediate segment, it is an IF. Why does it need to be "identified"?

Because sometimes there is a stepdown fix, or two, in the initial segment,
and sometimes there is a stepdown fix, or two, in the intermediate
segment. In that event you do not know which fix is the intermediate fix
(well, we're really speaking of waypoints since this is an RNAV-only
procedure).


OK, that helps. Although, as Roy said, it doesn't seem to matter much, the
distinction has become blurred. The controller is supposed to issue an
altitude restriction for the vector that is consistent with the MVA/MIA,
thus insuring obstacle clearance, so it is not obvious why IAF vs IF vs
stepdown fix really matters. But, the rule ought to be clear.

I had thought that all the fixes between an IAF (or the beginning of the
procedure) and the FAF are IFs (disregarding fix vs waypoint). Apparently
that is not true, given stepdown fixes on the initial segment. Don't think
I have seen one of those, but they seem to be allowed by TERPS. But I also
thought that all fixes on the intermediate segment were IFs. But that does
not seem to meet the definition of IF in the P/CG.

The altitude issue is a big problem with this business of vectoring to the
IF on RNAV approaches. If the IF altitude is not at or above MVA/MIA, the
approach may not be flyable with vectors to IF. 7110.65 does not give
guidance to controllers on that issue, that I can find.

Stan Prevost wrote:

"Sam Spade" wrote in message
...

Stan Prevost wrote:

"Sam Spade" wrote in message
...



What's to identify? If it is not an IAF, and not the FAF, and is on an
intermediate segment, it is an IF. Why does it need to be "identified"?

Because sometimes there is a stepdown fix, or two, in the initial segment,
and sometimes there is a stepdown fix, or two, in the intermediate
segment. In that event you do not know which fix is the intermediate fix
(well, we're really speaking of waypoints since this is an RNAV-only
procedure).



OK, that helps. Although, as Roy said, it doesn't seem to matter much, the
distinction has become blurred. The controller is supposed to issue an
altitude restriction for the vector that is consistent with the MVA/MIA,
thus insuring obstacle clearance, so it is not obvious why IAF vs IF vs
stepdown fix really matters. But, the rule ought to be clear.

Look at KSEA RNAV 16L. That was recently revised to designate the IF.
Prior to January 18 you had several fixes between the IF and the FAF and
you didn't know which one was the IF. I could search all night and find
some like this without IF designated. It was decided that sending an
aircraft to a fix within the IF is into a narrow area that is more
properly handled with vectors to final. But, where there are multiple
stepdown fixes in the intermediate odds are the MVA would be too high to
be compatible with descent requirements.

I had thought that all the fixes between an IAF (or the beginning of the
procedure) and the FAF are IFs (disregarding fix vs waypoint). Apparently
that is not true, given stepdown fixes on the initial segment. Don't think
I have seen one of those, but they seem to be allowed by TERPS. But I also
thought that all fixes on the intermediate segment were IFs. But that does
not seem to meet the definition of IF in the P/CG.

No, The IF is where the rampdown from initial widths to final segment
width begins and were 500 feet of obstacle clearance comes into play.
The fixes between the IF and FAF are just step-down fixes.

The altitude issue is a big problem with this business of vectoring to the
IF on RNAV approaches. If the IF altitude is not at or above MVA/MIA, the
approach may not be flyable with vectors to IF. 7110.65 does not give
guidance to controllers on that issue, that I can find.

Yes, it is there and clearly stated. In 4 (f) of 4-8-1 it states "at an
altitude that will permit normal descent..." Then the note defines that
as 300 feet per mile

(f)The aircraft is on a course that will intercept the intermediate
segment at an angle not greater than 90 degrees and is at an altitude
that will permit normal descent from the Intermediate Fix to the Final
Approach Fix.

NOTE−Controllers should expect aircraft to descend atapproximately 300
feet per NM when applying guidance insubpara 4(f) above

"Sam Spade" wrote in message
...
It was decided that sending an aircraft to a fix within the IF is into a
narrow area that is more properly handled with vectors to final. But,
where there are multiple stepdown fixes in the intermediate odds are the
MVA would be too high to be compatible with descent requirements.

OK, those are clear reasons for not going direct to a fix on the
intermediate segment other than the first one, the IF.


The altitude issue is a big problem with this business of vectoring to
the IF on RNAV approaches. If the IF altitude is not at or above
MVA/MIA, the approach may not be flyable with vectors to IF. 7110.65
does not give guidance to controllers on that issue, that I can find.

Yes, it is there and clearly stated.

It sure is. That's what I get for going from memory. Don't know how I
missed that the last time I looked at it, or if I just forgot it. Won't
forget it again.