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Driver170

MDA + 50 for a CDFA NPA

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Yeh a vertical path (glide path/GP in boeing speak/FMA) has been coded in the database. That is nothing new! it It is coded as a geometric path descent in degrees flightpath angle, usually around 3°. And VNAV constructs its whole descent path backwards from the runway waypoint and the EOD (end of descent) altitude.

Yea but may not always reflect the same flight path angle between published and VNAV constructs. This is why you its illegal to manually build the app in the FMC, atleast FAA. You have to pull it from the database because that path isn't constructed by the FMC, it is depicted as published. Again, this is why you have to compare the database app to the published app. I call it the SCAR check. 1.Select it from the database. 2.Check it against published charts(GP, ALTITUDES, COURSE, DISTANCES,ETC). 3.Activate it. 4. Raim check if it's a GPS or RNAV procedure.  If the app don't match, which 99% they do, I can't fly that app. sometimes the database app has an error or the FMS has an issue loading it probably.

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Well that gels with what I said, I think. You can do a LOC approach, if it is coded in the FMC. You can't select the ILS and do it in VNAV if cleared for a ILS GS OTS. We'd do it in V/S and use the LOC stepdowns and min.

Spin, I believe we have been saying the same thing all along. Based on your post, i think the disparity is in the way we view ILS and LOCs. It seems you may view ILS GS OTS and LOCs as different animals. In my flying they are the same. Anytime you are not following a GS, you are using the LOC mins. Most ILSs revert to LOCs when the GS is out of service. There are stand alone LOCs , such as when the terrain or course does not allow a GS. Good example is the LOC/DME-E at KASE. The point I was making to driver is that the LOC only app that's part of the FMC is good because its GP reflects published and meets the step down ALTs.

 

Either a difference in view or my initial post was not clear enough for ya.

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The 737NG allows you to use VNAV for LOC only type approaches. It's not recommended to do so when the LOC has step down fixes due to glide path and ALT limits.

 

 


The point I was making to driver is that the LOC only app that's part of the FMC is good because its GP reflects published and meets the step down ALTs.

 

I agree with the green. The red seems to disagree with the rest.

 

That's all I'm saying.


Matt Cee

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This conversation is interesting because our procedures make no distinction between an ILS with the glideslope inop and a localizer procedure, we fly them both the same in VNAV.  I did check and found that our ILS procedures in the FMC do have a coded glide path, do yours not?


Joe Diamond

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I agree with the green. The red seems to disagree with the rest.

ILS approaches with step-down fixes, flown as G/S OUT, may have a vertical angle that does not satisfy the published minimum altitudes. This means use of VNAV PTH may result in small deviations below minimum step-down altitudes, and therefore the use of VNAV PTH is not recommended

 

Do you not consider this a LOC approach? To me, they are all LOC approaches because there are no distinctions in my ops.

 

From the way I interpret that note, lets say I was arriving to an airport with an ILS and the G/S is NOTAMed out. I pull up the ILS chart on my EFB and it has step down fixes for the LOC. When I read the note, it's not recommended that I fly this LOC in VNAV due to the reason stated. Does that check with you or is it something I'm missing? This note is from the VNAV path constructs section. Honestly, I don't know how 737s do it since I don't fly them. My neighbor is a C-40 guy, but he is out on the road. I'll ask him, but Air Force guidance  can differ greatly from civil regs. I never understood why we were so different when flying the same aircraft. We do have some advantages in some ops compared to civilian operators. Flying a DC10 at 350 kts below 10,000ft during formation rejoin was always interesting. 

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ILS approaches with step-down fixes, flown as G/S OUT, may have a vertical angle that does not satisfy the published minimum altitudes. This means use of VNAV PTH may result in small deviations below minimum step-down altitudes, and therefore the use of VNAV PTH is not recommended

 

Do you not consider this a LOC approach?

 

Ok, I think we're getting somewhere. Or I'm getting somewhere. If I understand this, "don't fly the LOC-only approach by selecting the ILS because there might be step-downs."

 

I agree with that.

 

If you can select the LOC approach in the FMC, you're good for VNAV. (Because the step-downs will be honored.)

 

If you're flying the LOC approach by selecting the ILS in the FMC, don't use VNAV.

 

The key is if the LOC is in the box.

 

I think we're on the same page.

This conversation is interesting because our procedures make no distinction between an ILS with the glideslope inop and a localizer procedure, we fly them both the same in VNAV.  I did check and found that our ILS procedures in the FMC do have a coded glide path, do yours not?

 

They're coded with GP3.0 or whatever. The problem is that is you select the ILS in the FMC and use VNAV, it will follow that coded GP3.0 and not follow the stepdowns for the LOC-only.

 

In our manual it has the example of KLAX ILS25L. The approach has changed,  but it would have you drop below LADLE if you followed the ILS in VNAV. Kinda of the reverse for GAATE. If you follow the GS, you'll be below the stepdowns.


Matt Cee

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This conversation is interesting because our procedures make no distinction between an ILS with the glideslope inop and a localizer procedure, we fly them both the same in VNAV. I did check and found that our ILS procedures in the FMC do have a coded glide path, do yours not?

 

I'm no 737NG expert and I don't fly them.

 

ILS approaches with step-down fixes, flown as G/S OUT, may have a vertical angle that does not satisfy the published minimum altitudes. This means use of VNAV PTH may result in small deviations below minimum step-down altitudes, and therefore the use of VNAV PTH is not recommended

 

That's from the training manual, but i wouldn't know. I've seen manual conflict themselves from time to time. In the jets I've flown and the Gulfstreams, i would have to Change NAV source from FMS to NAV and use V/S.

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I'm no 737NG expert and I don't fly them.

 

ILS approaches with step-down fixes, flown as G/S OUT, may have a vertical angle that does not satisfy the published minimum altitudes. This means use of VNAV PTH may result in small deviations below minimum step-down altitudes, and therefore the use of VNAV PTH is not recommended

 

That's from the training manual, but i wouldn't know. I've seen manual conflict themselves from time to time. In the jets I've flown and the Gulfstreams, i would have to Change NAV source from FMS to NAV and use V/S.

 

This makes sense.  I took a look at the approaches in our database and while the ILS procedures do have a coded GP they don't include any step down fixes between the FAF and the runway, whereas the LOC procedures to the same runway do.

 

I'm a bit surprised the blurb from the Boeing training manual didn't make it into our operating manuals.  Just about everywhere we go has the LOC procedures in the database so it's not an issue that would come up often.  I'll have to ask about it at my next recurrent.


Joe Diamond

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