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Driver170

MDA + 50 for a CDFA NPA

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Can someone quote me from the ICAO DOC if a requirement to add +50 to commercial acft for a NPA like LNAV , LP and V/S (2D: without vertical guidance, flown to an MDA(H) ?

 

I know for APV - VNAV/LNAV LPV and PA - ILS all use DA(H) and this takes into account the height loss at DA(H) (3D: with vertical guidance, flown to a DA(H)

 

So NPA is LNAV V/S and LP all have MDA(H) but do you still add + 50 to the MDA(H)


Vernon Howells

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Well it depends on how you plan to fly the approach. The CDFA is a recommended technique with the benefits of a more stable approach. You are just flying the NPA like an ILS. As far as the approach goes, it depends on how you are flying it. If you are going down to a MDA using V/S /step down fixes and choose to level off at MDA, then fly it normally. If you are going to fly down using your own or FMS/FMC calculated guide path, you can go with a derived decision altitude,DDA = MDA + 50 for a go around point. Honestly, many guys don't like the DDA. It has you commit 50ft prior which means a go around if the weather is right at minimums. 

 

In all it's just a technique to stabilize your approach with out all the constant adjustment and changes.

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Good grief you like acronyms... very difficult to understand question.

 

Generally, the regulatory agencies (which ICAO is not, it is a standards body) don't regulate how to fly the airplane.  Company policies will speak to your issue, but say you are a wealthy individual with a Citation X then what is the requirement?  Don't bust minimums unless you have runway environment in sight, period.  It's probably a good idea to set minimum VNAV descent to some value higher than minimums, how much is up to your company or good judgement in the US (and probably globally).  I suspect that Boeing has some recommendations in the FCTM... did you look there?


Dan Downs KCRP

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So NPA is LNAV V/S and LP all have MDA(H) but do you still add + 50 to the MDA(H)

 

Only do this if you are flying an approach to an MDA and using VNAV coupled to your autopilot to controll your descent rate to the MDA. adding 50 ft to the MDA will give you a DDA (derived decision altitude). If you are using V/S to descend just use the published MDA. 

 

Since the 737 has VNAV and IAN (if you select it) you can for example, fly a VOR approach with the autopilot tracking the VOR for lateral guidance and VNAV controlling you vertical guidance. In this setup it would be appropriate to use a DDA (MDA+50).


9376034507_e7c13d7145.jpg

 

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If you are going down to a MDA using V/S /step down fixes and choose to level off at MDA, then fly it normally

 

Per EU OPS 1 no acft is allowed to level off at the MDA thats why they use the technique CDFA, and VNAV will fly this procedure from the database, so if i'm not using VNAV on an approach that doesn't have vertical guidance (NPA) i'll have to use an alternative way and that would be V/S but thats my question will i need to add + 50 at the VDP

Only do this if you are flying an approach to an MDA and using VNAV coupled to your autopilot to controll your descent rate to the MDA. adding 50 ft to the MDA will give you a DDA (derived decision altitude). If you are using V/S to descend just use the published MDA. 

 

Since the 737 has VNAV and IAN (if you select it) you can for example, fly a VOR approach with the autopilot tracking the VOR for lateral guidance and VNAV controlling you vertical guidance. In this setup it would be appropriate to use a DDA (MDA+50).

 

I found this in EU OPS

 

The MDA should be treated as DA, if operating according to the CDFA technique


Vernon Howells

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Per EU OPS 1 no acft is allowed to level off at the MDA thats why they use the technique CDFA, and VNAV will fly this procedure from the database, so if i'm not using VNAV on an approach that doesn't have vertical guidance (NPA) i'll have to use an alternative way and that would be V/S but thats my question will i need to add + 50 at the VDP

I'm a FAA certified guy and have not flown a CDFA type approach in Europe since my SOPs state that you will make most precise approach available. Ive yet to have to fly a non precision approach in the places we fly to in Europe. In the states, it depends on how I'm flying the approach. The DDA altitude and CDFA is encouraged but not a must in my ops. This is why guys in my outfit opt for MDA. We do fly them during training and proficiency SIMs to be familiar in the event we have too.

 

Could you please post the exact paragraph of you reference you are mentioning. I'd like to see its exact wording and how it reads in EU OPS 1.

 

I was looking over this info, but would like to see your reference.

http://www.theairlinepilots.com/forumarchive/quickref/euopsjeppesen.pdf

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Aerodrome operating minima — General

(See Appendix 1 (old) and Appendix 1 (new) to OPS 1.430)

 

 

(d)2. All non-precision approaches shall be flown using the continuous descent final approaches (CDFA) technique unless otherwise approved by the Authority for a particular approach to a particular runway. When calculating the minima in accordance with Appendix 1 (New), the operator shall ensure that the applicable minimum RVR is increased by 200 metres (m) for Cat A/B aeroplanes and by 400 m for Cat C/D aeroplanes for approaches not flown using the CDFA technique, providing that the resulting RVR/CMV value does not exceed 5 000 m.

 

 

Its somewhat a complicated issue for sure! What i have found is, in the EU everyone has to fly NPAs as CDFA (Continous Descent Final Approach) and in those there is no MDA anymore, only a DA. Wether you have to add something to the published DAs depends on your operator (airline). Some do, some don't. I think this is pretty much correct ?


Vernon Howells

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Correct, it's up to the operator if you are using an add-on when going down to a DA. Again, if using JEPPS, we do, the approach will be depicted as CDFA with DAs. In this case, I see no benefit with an add on. You will go missed if weather is right at mins. I have no issues with the CDFA, we have always flown NPAs that way, but with preference to get down a little early to have a chance to see the runway at mins. Stay there until timing/DME expires at the MAP. Luckily for me, while transiting European fields, the ILS has always been the option. Since we use JEPP FD and manuals exclusively, if a CDFA is depicted, we would fly it. In my ops, we are not required to use an add on when going down to a DA. In the states, if flying to MDA mins, we have the option of using a DDA or doing it old school. That's until the FAA get around to doing the same as EURO as they have announced. Looking at some other data, there seem to be some cases in which a CDFA approach would not be possible, I.E. terrain or circling.

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Cheers rick!

 

Well i was using LNAV V/S for a while on the 737NGX then decided to use LNAV/VNAV for every NPA except for a LOC approach in which case i would use LOC/VNAV. But now starting to use IAN, like you know the procedure and indication is the same as for an ILS, although one has to be aware that the GP is database computed based on the QNH on the side of the Master FCC :0

 

Does all NDB, VOR, LOC app now have a computed glide path from the FMS on the 737 NG ? 


Vernon Howells

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That's until the FAA get around to doing the same as EURO as they have announced.

 

I'm pretty sure this is part of the next project I'm working on as part of my new day job, actually.


Kyle Rodgers

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Does all NDB, VOR, LOC app now have a computed glide path from the FMS on the 737 NG ?

Yes, the FMC for the 737NG and most modern FMC systems has the approach designed glide path in the data base. Prior to the approach, we actually compare the course and glide path from the FMC to the actual approach depiction on the chart. They should match to ensure a protected approach. As far as the localizer goes, in my jet and other jets I've flown, you must fly the localizer in green(NAV RADIO SOURCE) and no VNAV. 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. You can also fly it in IAN.  

 

 

 


I'm pretty sure this is part of the next project I'm working on as part of my new day job, actually.

I bet, lots of changes to come.

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It's not recommended to do so when the LOC has step down fixes due to glide path and ALT limits.

 

Haven't heard that before. The only time we don't use VNAV for NPA is ILS w/GS OTS and there is no coded LOC approach. Then its V/S.


Matt Cee

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Haven't heard that before. The only time we don't use VNAV for NPA is ILS w/GS OTS and there is no coded LOC approach. Then its V/S.

As I inferred, I don't have a 737 qual, but this is in the training manual:

 

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. Published localizer (LOC) only approaches are compatible with VNAV PTH.

 

I mentioned in my earlier post that the 737 allows LOC only approaches. Again in my OPS with Gulfstream, we can't shoot the ILS or LOC with the FMS for this reason. FMS calculated glide path may not coincide with the depicted step downs which are mostly geared for the LOC.  Again, I don't fly the NG, just what I saw in the training manual.

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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. Published localizer (LOC) only approaches are compatible with VNAV PTH.

 

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.


Matt Cee

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Yes, the FMC for the 737NG and most modern FMC systems has the approach designed glide path in the data base. Prior to the approach, we actually compare the course and glide path from the FMC to the actual approach depiction on the chart. They should match to ensure a protected approach. As far as the localizer goes, in my jet and other jets I've flown, you must fly the localizer in green(NAV RADIO SOURCE) and no VNAV. 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. You can also fly it in IAN.

 

 

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.

 

Thats what i know haha


Vernon Howells

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