Hey Everyone.
I’ve been reading the forum for along time, and finally decided to create an account to ask this specific question. Maybe someone out there can answer it for me. Why is it that on the RNAV 16 approach to CYXL, the transition height between the ‘T’ Bar fixes (i.e. DUTUN to RORLI) is 4500’ when the MSA is 3000’ This confuses me greatly. I think it’s similar for 34, but don’t remember for sure. I was on approach to YXL the other night at 3AM, and the captain and I were talking about how bizarre it was. Doesn’t the MSA mean you can be 25nm in any direction from the specified fix, and be safe? Yet according to the approach plate, between those two points (which are defiantly within that 25nm radius) you have to be at 4500’??? Does this make sense to anyone else? Maybe someone who works 32.2 can explain it to me.
Thanks
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When once you have tasted flight, you will forever walk the earth with your eyes turned skyward,
for there you have been, and there you will always long to return.
cpl_atc wrote: Additionally, an adjustment was made at the same time to the 5nm fix for the 16 approach in order to promote separation between float ops on the north side of the airport. Practically speaking this makes little sense, because most aircraft cancel IFR during VMC, which renders the approach alititudes totally irrelevant.
I know that at a few other sites (no idea about YXL) they've looked at class-G corridors to help out busy float traffic in IMC, so that SVFR isn't always required. Changing the 5 mile fix around may be to help facilitate something like that.
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no sig because apparently quoting people in context is offensive to them.
All RNAV approaches nationwide have been modified, or will eventually be modified, to provide a simulated glideslope-type rate of descent between the fixes. This is tied into preparations related to WAAS operations. It is a bit goofy in the sense that the altitudes, in this case (at YXL), are not related to terrain or obstacle clearance.
Obviously you are not a certified Instrument Approach designer as demonstrated by your above statement………….. Your comments in this particular area must be taken with a grain of salt!!!!!
Ok, so let me ask this... Is it a legal requirement to stay at or above 4500' between these two points? If you flew the approach at the 25nm safe altituded between these two waypoints, are you considered to be breaking mins???
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When once you have tasted flight, you will forever walk the earth with your eyes turned skyward,
for there you have been, and there you will always long to return.
Always fly the published altitudes as presented. To answer your specific question there have been instances where enroute altitudes(MSA) are lower that procedural altitudes(procedure turn, IAWPL and IAWPR) and it can be for several reasons. Keeping all segments of the procedure in controlled airspace is one example also line of site standard localizer intercepts created by ICAO coverage volumes(for ILS and/or LOC/DME IAPs) is another..
I am of the opinion if you have to raise any procedural altitude above a published enroute altitude for whatever reason, keep both altitudes the same but others in this field have different viewpoints.
The explanation we were given was the same as grimey's take, to keep the IFR away from float traffic. Having said that, I am kind of curious of what the ramnifications of being at or above 3000 (MSA) but below the 4500' from a legal standpoint. I always preferred going straight to the 5 mile fix at 3000' which is very close to a 3 to 1 to the thresh-hold. Wonder if I was breaking the law?
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"Hell, I'll fly up your ass if the money's right!"
Orlando Jones - Say It Isn't So
I'm pretty sure you wouldn't be breaking the law in that case. You are not required to go to one of the "T" fixes. TOVAX and (whatever the other one is called for 16) can be used as the first fix along the the approach. If this is the case those 4500ft alts don't even come into play and your published min IFR alt is 3000.
There is a similar discrepency in YSB for the Arc altitudes vs the MSA. I've been told that it allows you to stay under radar coverage while flying the initial portion of the approach. I don't know exactly what alt Winnipeg will pick you up at YXL but most of us aren't calling them up on departure until around 4000. The other explanations all make sense too. Who knows.
"This is tied into preparations related to WAAS operations."
Well, the above is your quote and my question is how did you determine that statement outside of "being your personal opinion".
"All RNAV approaches nationwide have been modified, or will eventually be modified, to provide a simulated glideslope-type rate of descent between the fixes".
Really!!!! that is news to many. Vertical guidance on final is currently available from any FMS equipped aircraft that loads up an IAP be it RNAV(GNSS) or a overlayed conventional procedure and has been this way for some time. WAAS(which is entirely new criteria) adds a new dimension called LVP(Localizer Performance with Vertical Guidance) and has published DA(Decision Altitude)
55+, my understanding on LPV approaches is that TSO 129 FMSs will be able to do them without the WAAS upgrade on the GPS provided they are also doing the RNAV thing with traditional aids.
In other words most FMSs with GPS installed in the last 10 years or so are currently able to do any LPV approach published as long as the temps are ISA or above.
ahramin wrote:55+, my understanding on LPV approaches is that TSO 129 FMSs will be able to do them without the WAAS upgrade on the GPS provided they are also doing the RNAV thing with traditional aids.
In other words most FMSs with GPS installed in the last 10 years or so are currently able to do any LPV approach published as long as the temps are ISA or above.
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My own understanding is LVP IAPs can only be flown using WAAS(TSO C145a/146a) avionics, however LNAV/VNAV procedures can be flown with TSO 129 avionics if such have Baro/VNAV capabilities. Most , if not all FMS have temp comp consequently the published temp limitations - PLAN VIEW Operational Notes are not an issue.
I don't profess to be an expert of avionics so I stand to be corrected.
55+ wrote:"This is tied into preparations related to WAAS operations."
Well, the above is your quote and my question is how did you determine that statement outside of "being your personal opinion".
Because that's what I was told by NC staff involved with the changes.
55+ wrote:
"All RNAV approaches nationwide have been modified, or will eventually be modified, to provide a simulated glideslope-type rate of descent between the fixes".
Really!!!! that is news to many. Vertical guidance on final is currently available from any FMS equipped aircraft that loads up an IAP be it RNAV(GNSS) or a overlayed conventional procedure and has been this way for some time.
Sigh. You will note that I specifically noted that approaches either had been modified, or "will eventually be modified" with this criteria. And I know that certain equipment will provide the vertical guidance. That is why I also specifically said that I thought it was misguided to try and force a pilot without that equipment to fly the same type of profile.
In future, how about reading my posts thoroughly.
"My personal opinion (I do not speak for NC here) is that it is stupid to design approaches this way."
Again here is your statement and you follow it up with.......... "that's because I was told by NC staff involved". If you word your statements correctly without ambiguity one could make a reasonable interpretation of what you are trying to say.
"That is why I also specifically said that I thought it was misguided to try and force a pilot without that equipment to fly the same type of profile."
What!!! where did you come up with this. The pilot(he or she) is not forced to do anything because published altitudes have to meet the required descent gradients for the particular segment. Final approaches are based on 318ft/nm which gives a vertical path angle of 3 degrees. The max allowed is 400ft/nm which is a VPA of 3.7deg. An approach can still be flown LNAV MDA without vertical reference.
Incidently, a pilot can fly a vertical profile referencing altitude, airspeed(IAS) and rate of descent only without software calculations from FMS equipped aircraft and it is certainly safe to do so.
"I am not making these points up for the sake of arguing with someone like yourself who apparently does not understand how the changes affected the approach as compared to its original state."
Oh,my. Now I understand why the NC - AIS procedure designers(TP-308 Vol 3 and FAA 8260.ch19B) have had difficulties dealing with CZUL/CZYZ........... what can one say!!!
Well………… guess I have been told to depart the fix with my meaningless TP-308 – Criteria for the Development of Instrument procedures+ RNAV GNSS badge. With that, . in the ATPL with the low time industry 7000hrs (including turbine/turbojet, FMS and the like) operating in the airspace that you talk about. Dare I mention my time working with TC/NC to boot doing the very work you talk about, naw didn’t think so.
I have been humbled by you as an individual who seemed to be well versed in all aspects of aviation, and at the same time lock wired in a permanent pissed-off position. I promise to crawl off with my book and not be heard from again, not to any dark rooms though where the mighty ATS have their hands on the pulse of aviation.[/color]
This confuses me greatly. I think it’s similar for 34, but don’t remember for sure. I was on approach to YXL the other night at 3AM, and the captain and I were talking about how bizarre it was. Doesn’t the MSA mean you can be 25nm in any direction from the specified fix, and be safe? Yet according to the approach plate, between those two points (which are defiantly within that 25nm radius) you have to be at 4500’??? Does this make sense to anyone else? 
Maybe someone who works 32.2 can explain it to me.
