Cows Go Moo
Yes, I said moo.
- Joined
- Jan 8, 2004
- Posts
- 70
"When assigned, intercept glidepath at xxxx..." note on simultaneous ILS approaches
Okay. This one is tough, and I know it's tough because I've personally had conversations with FAA people in OKC, a FSDO, and a TRACON about this and still have no clear answer.
We see this note in the profile view of approach charts of approaches which may conduct simultaneous ILS approaches (both PRM and non-PRM): When assigned by ATC, intercept glidepath at xxxx, xxxx, or xxxx (altitudes). These altitudes are at intermediate fixes on a final approach course at airports which could be characterized by a Class B airspace, a long final approach course, and parallel runways/approaches. They aren't too hard to find ... DFW, LAX, ORD, PHL, etc.
If that note were not there, the clear, right thing to do is to regard each intermediate fix altitude as a minimum crossing altitude regardless of where the glideslope is. (Some approaches have mandatory, maximum, and recommended altitudes published, but those are very unusual.) Joining the glideslope at an altitude higher than the published glideslope intercept altitude (that's the altitude immediately outside the profile glideslope feather, generally 1500-1800 feet AGL) can in some cases put an aircraft below the intermediate fix crossing altitudes which has the potential of causing a loss of vertical separation with traffic getting turned onto a parallel approach course. So that's the right thing to do without the note.
With the note, opinions vary, and the problem is the word "assigned." What is that? At ORD this is an issue with their triple west approaches. On a parallel simultaneous approach to 27L, the clearance might go something like this: "... cross RIPPR at 6000, cleared ILS 27L approach." (It's usually GRABL at 7000, but I'm trying to make a point here.) That's what we hear. The note says, "When assigned by ATC, intercept glidepath at 4000, or 5000, or 6000." (4 and 5 correspond to EBENS and BASHH) So ... what's an assignment? We were assigned the approach. We were assigned 6000. Does that allow us to intercept the glideslope at 6000? Or does "assignment" mean an explicit instruction that says to intercept the glideslope at 4000, 5000, or 6000. Example: "... cross RIPPR at 6000, intercept the glidepath at 6000, cleared ILS 27L approach." I've never heard anything like that and I don't believe there is any such phraseology for it.
Complicating things is that I'm pretty sure simultaneous approaches are flight checked and designed for early glideslope intercept at those higher altitudes. The AIM talks about it. Aircraft getting turned onto parallel approaches must do so at different altitudes with different, alternate glideslope intercept altitudes. If you look at the Attention all Users page for PRM approaches, one of the notes says something like, "Descent on the ILS glideslope ensures complying with all crossing restrictions." PRM approaches are nearly the same in terms of basic design as non-PRM simultaneous approaches. I think the glideslope is supposed to put you at or above the crossing fixes, but in some places like ORD and LAX it does not.
Even more fun, the Chicago TRACON has made it pretty clear that, note or no note, they depend on aircraft to meet each of those crossing restrictions in order to maintain separation. They do not want us to intercept the glideslope before the default glideslope intercept altitude ... 2200 for all three approaches 28, 27L, and 27R.
Wondering if any pilots or controllers out there have good, solid information and/or references for what "assignment" means.
Okay. This one is tough, and I know it's tough because I've personally had conversations with FAA people in OKC, a FSDO, and a TRACON about this and still have no clear answer.
We see this note in the profile view of approach charts of approaches which may conduct simultaneous ILS approaches (both PRM and non-PRM): When assigned by ATC, intercept glidepath at xxxx, xxxx, or xxxx (altitudes). These altitudes are at intermediate fixes on a final approach course at airports which could be characterized by a Class B airspace, a long final approach course, and parallel runways/approaches. They aren't too hard to find ... DFW, LAX, ORD, PHL, etc.
If that note were not there, the clear, right thing to do is to regard each intermediate fix altitude as a minimum crossing altitude regardless of where the glideslope is. (Some approaches have mandatory, maximum, and recommended altitudes published, but those are very unusual.) Joining the glideslope at an altitude higher than the published glideslope intercept altitude (that's the altitude immediately outside the profile glideslope feather, generally 1500-1800 feet AGL) can in some cases put an aircraft below the intermediate fix crossing altitudes which has the potential of causing a loss of vertical separation with traffic getting turned onto a parallel approach course. So that's the right thing to do without the note.
With the note, opinions vary, and the problem is the word "assigned." What is that? At ORD this is an issue with their triple west approaches. On a parallel simultaneous approach to 27L, the clearance might go something like this: "... cross RIPPR at 6000, cleared ILS 27L approach." (It's usually GRABL at 7000, but I'm trying to make a point here.) That's what we hear. The note says, "When assigned by ATC, intercept glidepath at 4000, or 5000, or 6000." (4 and 5 correspond to EBENS and BASHH) So ... what's an assignment? We were assigned the approach. We were assigned 6000. Does that allow us to intercept the glideslope at 6000? Or does "assignment" mean an explicit instruction that says to intercept the glideslope at 4000, 5000, or 6000. Example: "... cross RIPPR at 6000, intercept the glidepath at 6000, cleared ILS 27L approach." I've never heard anything like that and I don't believe there is any such phraseology for it.
Complicating things is that I'm pretty sure simultaneous approaches are flight checked and designed for early glideslope intercept at those higher altitudes. The AIM talks about it. Aircraft getting turned onto parallel approaches must do so at different altitudes with different, alternate glideslope intercept altitudes. If you look at the Attention all Users page for PRM approaches, one of the notes says something like, "Descent on the ILS glideslope ensures complying with all crossing restrictions." PRM approaches are nearly the same in terms of basic design as non-PRM simultaneous approaches. I think the glideslope is supposed to put you at or above the crossing fixes, but in some places like ORD and LAX it does not.
Even more fun, the Chicago TRACON has made it pretty clear that, note or no note, they depend on aircraft to meet each of those crossing restrictions in order to maintain separation. They do not want us to intercept the glideslope before the default glideslope intercept altitude ... 2200 for all three approaches 28, 27L, and 27R.
Wondering if any pilots or controllers out there have good, solid information and/or references for what "assignment" means.
