How do you identify Cabav?

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Embatr

Guest
Hi everyone. I wanted to throw this out to see if I'm in the wrong on my understanding of this. Thanks for your input. This approach is the ILS 27 in MEM

The question is how does the pilot know, or identify CABAV final approach fix so they can begin timing and let down to MDA? In this scenario the glideslope is out of service, and the pilot will circle-to-land 18R. I've always been under the assumption that since (1) Radar is required, and that (2) CABAV is listed as a radar fix, that the controller will simply call out the fix as you pass it. However some of my colleagues say that it is the pilot's responsibility to determine when they've passed the fix. They say that you can identify CABAV via the MEM 068 radial. I'm not so sure that that is correct.

So there you have it, if anyone has the answer and can help me out, I'd appreciate it... thoughts and opinions are just as welcome.
 
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I haven't quite figured out how to paste in the picture of the approach plate, when I have more time I'll give it another shot but I've got to go for now...
 
Embatr said:
Hi everyone. I wanted to throw this out to see if I'm in the wrong on my understanding of this. Thanks for your input. This approach is the ILS 27 in MEM

The question is how does the pilot know, or identify CABAV final approach fix so they can begin timing and let down to MDA? In this scenario the glideslope is out of service, and the pilot will circle-to-land 18R. I've always been under the assumption that since (1) Radar is required, and that (2) CABAV is listed as a radar fix, that the controller will simply call out the fix as you pass it. However some of my colleagues say that it is the pilot's responsibility to determine when they've passed the fix. They say that you can identify CABAV via the MEM 068 radial. I'm not so sure that that is correct.

So there you have it, if anyone has the answer and can help me out, I'd appreciate it... thoughts and opinions are just as welcome.
Click to expand...

Your colleagues are correct.
 
His colleagues are partly correct. The controller will not automatically call CABAV, but since it's a published radar fix, you can request s/he do so if, say, you have only one VOR/LOC receiver and don't want to be switching back and forth. However, the reason it says RADAR REQUIRED is that there is no IAF or other route to join the approach other than vectors to final, not that the only way to identify CABAV is radar.
 
The angle of the crossing radial MEM068 is not offset enough from the inbound course to accurately define CABAV to initiate the timing for a LOC only approach. Draw out the radials with the allowed slop tolerances and you have a pretty wide box at CABAV. One might consider using the ILS capture altitude to start timing if Comms were to quit. You cross CABAV exactly at glide slope intercept at 1900MSL. To me that would be an emergency with no Comms.

You notice that COVIM is the "IF" or Initial Fix is also RADAR REQUIRED with a reference crossing radial (HLI 322R), but it is not a published transition.
 
BillTIZ said:
The angle of the crossing radial MEM068 is not offset enough from the inbound course to accurately define CABAV to initiate the timing for a LOC only approach. Draw out the radials with the allowed slop tolerances and you have a pretty wide box at CABAV.
Click to expand...

I see the potential for a bit less than half a mile error at CABAV using the crossing radial +/-4 degrees on the LOC centerline, a bit more if you include something for the LOC center tolerance. In any case the only reason that R068 is depicted is for identifying CABAV so I have to assume that it's adequate for that purpose.

One might consider using the ILS capture altitude to start timing if Comms were to quit. You cross CABAV exactly at glide slope intercept at 1900MSL. To me that would be an emergency with no Comms.
Click to expand...

If you have a GS receiver and the GS ground station is OK why wouldn't you fly the ILS?

You notice that COVIM is the "IF" or Initial Fix is also RADAR REQUIRED with a reference crossing radial (HLI 322R), but it is not a published transition.
Click to expand...

I disagree. Radar is required because there's no published path to the final approach course, but I believe that ATC could vector you onto the LOC prior to COVIM and expect you to identify that fix yourself using HLI322.
 
BillTIZ said:
The angle of the crossing radial MEM068 is not offset enough from the inbound course to accurately define CABAV to initiate the timing for a LOC only approach. Draw out the radials with the allowed slop tolerances and you have a pretty wide box at CABAV.
Click to expand...

The along track fix displacement error is 1.20 miles east of CABAV and 0.92 miles west of it. The maximum error for a FAF is normally one mile, but may be up to two miles if a buffer of length equal to the excessive fix error is provided between the published MAP and the point where the missed approach surface begins.

You notice that COVIM is the "IF" or Initial Fix is also RADAR REQUIRED with a reference crossing radial (HLI 322R), but it is not a published transition.
Click to expand...
"RADAR REQUIRED" is due to the absence of feeder routes, radar is not required to determine COVIM or CABAV.
 
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BillTIZ said:
The angle of the crossing radial MEM068 is not offset enough from the inbound course to accurately define CABAV to initiate the timing for a LOC only approach. Draw out the radials with the allowed slop tolerances and you have a pretty wide box at CABAV. One might consider using the ILS capture altitude to start timing if Comms were to quit. You cross CABAV exactly at glide slope intercept at 1900MSL. To me that would be an emergency with no Comms.

You notice that COVIM is the "IF" or Initial Fix is also RADAR REQUIRED with a reference crossing radial (HLI 322R), but it is not a published transition.
Click to expand...

Oh, god, are we gonna start debating timing an ILS again? Stop the insanity!
 
lancefisher said:
I see the potential for a bit less than half a mile error at CABAV using the crossing radial +/-4 degrees on the LOC centerline, a bit more if you include something for the LOC center tolerance. In any case the only reason that R068 is depicted is for identifying CABAV so I have to assume that it's adequate for that purpose.
Click to expand...

To determine fix displacement error a crossing course accuracy of plus-or-minus 3.6° is used for VOR or TACAN radials, plus-or-minus 0.5° for a localizer course, and plus-or-minus 5° for NDB bearings. I don't see how you came up with less than half a mile error at CABAV. I made the fix error to be 0.92/1.20 miles using an intersection angle of 23.16° between the MEM R-068 and the localizer and 6.61 NM between MEM and CABAV.


I disagree. Radar is required because there's no published path to the final approach course, but I believe that ATC could vector you onto the LOC prior to COVIM and expect you to identify that fix yourself using HLI322.
Click to expand...

You are correct.
 
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BillTIZ said:
The angle of the crossing radial MEM068 is not offset enough from the inbound course to accurately define CABAV to initiate the timing for a LOC only approach.
Click to expand...
If that were true, it wouldn't be defined that way on the chart.
One might consider using the ILS capture altitude to start timing if Comms were to quit.
Click to expand...
A 30-degree crossing angle isn't good enough for you, but a 3-degree angle is? In any event, if you lose comm and have the GS, why in the world would you do it any way other than as a full ILS? Sure, backup timing is fine in case the GS quits after the FAF, but use the cross-radial for that -- much better angle.

And if you do have comm but can't get CABAV on the VOR (station is down, #2 VOR is down, etc), you can always ask the controller to call it for you -- that's what "RADAR" next to the fix means.
 
1 - Not debating timing the ILS.. I was always taught to start the clock just in case the GS failed and you could resort to LOC only minimums. But then again most of the ILS/LOC around here have DME with no timing box for the LOC only mins.

2 -
Quote:
You notice that COVIM is the "IF" or Initial Fix is also RADAR REQUIRED with a reference crossing radial (HLI 322R), but it is not a published transition.
Quote reply: ""RADAR REQUIRED" is due to the absence of feeder routes, radar is not required to determine COVIM or CABAV. ""

I think that's what I said -- "no published tranistion".
 
BillTIZ said:
Quote reply: ""RADAR REQUIRED" is due to the absence of feeder routes, radar is not required to determine COVIM or CABAV. ""

I think that's what I said -- "no published tranistion".
Click to expand...

No, you said COVIM is also RADAR REQUIRED. Twice. Radar is not required to determine COVIM.
 
BillTIZ said:
1 - Not debating timing the ILS.. I was always taught to start the clock just in case the GS failed and you could resort to LOC only minimums. But then again most of the ILS/LOC around here have DME with no timing box for the LOC only mins.
Click to expand...
I teach timing the ILS not so much so you can make an LOC out of it, but rather so you know when to start the missed approch turn if the GS fails. If you don't time, and there's no MM (an increasingly common situation), you may have no other way to tell when you've reached the MAP. And, as we all should know, you don't want to be turning either too soon or too late on a missed approach, lest you hit the reason the turn is positioned where it is.
 
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