Hello,

 

What is the lowest RNP cat appch the NGX is capable of?  I flew the RNAV (RNP) Z RWY 16L into KSEA and had to use the min's for RNP 0.30 DA since I was unable to input 0.12 into the FMC for the lower min's.  Is this even possible?  It seems that since the ANP is usually around .02 this shouldnt be an issue.

 

Thanks,

 

Steve

I couldn't find anything specific in the manuals regarding such RNP limitations, so I guess you are correct: you can fly any RNP approach as long as the Actual Navigation Performance (ANP) stays within the limits established by the chart.

 

Also, I don't think the FMS will accept RNP values with more than one decimal place. Try entering 0.1 instead. That should work.

Hello,

 

Thanks. I will try using just the single value after the decimal. I wasn't sure if its a limitation of NGX or an input "sequence." From what I have read the FMC always allows you to fly the RNP appch of the most restrictive min's without user input, but if you wish to actually fly the lower min's you must actually input the RNP DA value. I'm not 100% certain though.

 

Thanks.

 

Steve Ortega

The only RNPs I have come across for RNAV approaches are 0.3 and 0.1 and these values can be input to the LEGS page or PROG page 4. You may see other values depending if you are in the airway, arrival, non RNAV approach, missed approach, etc.

 

A 0.1 RNP approach is known as RNP AR (Authorization Required) and required special certification and are usuall denoted as "RNAV RNP" on the chart. Most RNAV approaches are 0.3 and are usually called "RNAV GNSS" or "RNAV GPS" on the chart.

 

If the LEGS page or PROG page 4 doesn't show the correct RNP just change it through the CDU scratch pad.

 

The minimums are set usual as BARO on the PFD using the EFIS Control Panel according the procedure. Remember to add 50' to the minimums for a 3.0º slope as all RNAV approaches constant descent approach (CDAs) and perhaps more than 50' is the slope a steeper - some operators take account of steeper slopes some don't.

Hello,

 

I reflew the same appch into KSEA and was successful in inputting 0.1 into the CDU.  I do believe though that I should be able to input 0.12 as this is on the appch chart.  I am not absolutely sure of this as I am not a real B737 pilot :(.

Also, some of the radius to fix dont look so RF.  Some are more straight line instead of curved.  Is this a NGX display or data quirk?  I am using the NavData Pro set as I understand that at this point Navigraph does not yet support this feature.

 

Thanks,

 

Steve Ortega

 

 

What is the lowest RNP cat appch the NGX is capable of?

 

As long as the ANP is lower than the RNP, in the sim, you can shoot the approach.  The limitations in the real world are mainly that of a stupid amount of red tape, crew certification, aircraft certification, and training (to follow the same two [darned] dots on the PFD), but in the end, the only real limitation is the aircraft's ability to know where it actually is (ANP), versus what's required for that segment (RNP).

 

Sorry - touchy subject with me, as this is one of the projects a team I'm working with is working on (BEBS, if you're curious), and it's proving rather frustrating.

 

 

 

A 0.1 RNP approach is known as RNP AR (Authorization Required) and required special certification and are usuall denoted as "RNAV RNP" on the chart. Most RNAV approaches are 0.3 and are usually called "RNAV GNSS" or "RNAV GPS" on the chart.

 

This isn't entirely accurate.

The precision does not dictate the fact that it's AR or not.  The KJFK RNAV RNP 04L is a perfect example, with 0.3 as its required performance (yet is still authorization required).  While more precise approaches are often RNP-AR, the value isn't the trigger for the -AR.  The value may, however, trigger what DA you use (as in the case of KDCA RNAV RNP 19

 

There are different types of approaches:

RNAV GPS

RNAV RNP (which includes GNSS in RNP 0.3 and below)

RNAV RNP-AR (Authorization Required)

 

If you look around at approaches, you'll find that most all of the RNAV RNP approaches in the States are RNP-AR, though the two are meant to be independent.  The reason AR is supposed to exist is for special, non-normal procedures.  While many approaches merit that designator (KDCA RNAV RNP 19 would be an example, given its oddities and proximity to obstacles/P-airspace), there are several others that do not (KIAD RNAV RNP 01C is essentially an ILS overlay - clearly meriting special attention...right?).  This is one of my aforementioned beefs with the system, but I'll spare you that rant.

 

 

Also, some of the radius to fix dont look so RF.  Some are more straight line instead of curved.  Is this a NGX display or data quirk?

 

Radius-to-Fix is not implemented because of a data access issue (at the time, at least).

The NGX doesn't recognise the second decimal place. I.e. the FMCS won't recognise a lateral RNP value of 0.10, but it'll accept 0.1. So Lateral RNP values like 0.12, 0.15, 0.18 etc won't work.

Aircraft that are capable and approved for RNAV (RNP) AR operations, are capable of accepting those values no problems.

If the weather is good, consider leaving the default value in (0.30) so you don't have to delete your manual entry in the event of a missed approach.

Brian Nellis.

Hello,

 

Really good information. Scandinavian13 thanks for the link. Interesting ready though slow. In the sim ANP is always good. I cant think of any reason why I wouldn't be able to shoot an RNP appch using the lowest min's or why my tolerances would ever go yellow inside the FAF, Unless mag dec changed so much between FSX inception and current data base, but even then I'm not sure.

Thanks copper. NGX can only do one decimal place. Figured that one out. But as mentioned above in FSX it doesn't really matter.

Also, when is it appropriate to change the MCP altitude to your missed appch alt? Doing so with LNAV and VNAV engaged and auto pilot still active seems to effect the NGX. Is it always done after disabling auto pilot? Got to love this stuff.... :-)

 

Thanks,

 

Steve Ortega

Hello,

 

Really good information. Scandinavian13 thanks for the link. Interesting ready though slow. In the sim ANP is always good. I cant think of any reason why I wouldn't be able to shoot an RNP appch using the lowest min's or why my tolerances would ever go yellow inside the FAF, Unless mag dec changed so much between FSX inception and current data base, but even then I'm not sure.

Thanks copper. NGX can only do one decimal place. Figured that one out. But as mentioned above in FSX it doesn't really matter.

Also, when is it appropriate to change the MCP altitude to your missed appch alt? Doing so with LNAV and VNAV engaged and auto pilot still active seems to effect the NGX. Is it always done after disabling auto pilot? Got to love this stuff.... :-)

 

Thanks,

 

Steve Ortega

I believe the earliest you should reset the MCP to missed alt is when you're 300' below that altitude on the approach. The latest would be on the missed approach itself. Your SOP should fall somewhere on that spectrum.

 

 

This isn't entirely accurate.

The precision does not dictate the fact that it's AR or not.

We don't do RNP AR and I am not specifically trained and thus I confidently assumed...incorrectly Good info and thanks for the correction Kyle.

 

 

Good info and thanks for the correction Kyle

 

Welcome!  To be honest, it would all still be foreign to me unless I was working on a project for it with my company.

Gents,

 

The NGX canot fly any RNP approach which requires RF legs.  RF is not modeled in the NGX.

 

JW

The NGX canot fly any RNP approach which requires RF legs.  RF is not modeled in the NGX.

 

See post #6...

 

 

 

I cant think of any reason why I wouldn't be able to shoot an RNP appch using the lowest min's or why my tolerances would ever go yellow inside the FAF, Unless mag dec changed so much between FSX inception and current data base, but even then I'm not sure.

 

Think failures  :wink:

 

If I lose GPS, the IRS stays accurate but its error in position calculation increases over time.  If the GPS fails relatively close to arrival and the ANP is still within what's needed, I can still shoot the approach.  If it failed early in the cruise, I might not be able to.

ANP predictions can also be an inhibiting factor as to what RNP is used for the approach.

 

Brian Nellis.

Hello,

 

If a GPS failure occurs would my only indication be a switch from "GPS" to "IRS" in the ND display and maybe an FMC msg? Meaning a lateral or vertical error indication is displayed only because either the primary, secondary, or even 3rd backup has gone OTS? If so, would this mean an out of limits caution would be advisory only and execution of the appch would still be allowed because you have an ANP value that is still better than the required RNP value? Or do you only get an error when all this equipment has failed all together(outside factors not withstanding) forcing a discontinuation of the appch? Lastly, wouldn't the failure backup sequence actually be....GPS, Radio Nav, ADIRU? Still learning......... :-)

 

Thanks

 

Steve Ortega

 

Wondering if PMDG has plans to update the NGX for RF.