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MELKOR

JS41 RNP Capable?

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Captians,I can neither find any documentation in manuals (or on the Net) as to whether or not the JS41 is RNP (Required Navigation Performance) capable, nor do I know enough about RNP to determine that myself.Does anyone know?Thanks.


- William Ruppel, CYKF, VATSIM 816871

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Bill-I can't speak for other airlines, but ours were NOT RNP certified.The FMS on this airplane is effectively a glorified first generation GPS device. Works reliably and runs well- but not capable of the fancy mathematics required for RNP compliance.


Robert S. Randazzo coolcap.gif

PLEASE NOTE THAT PMDG HAS DEPARTED AVSIM

You can find us at:  http://forum.pmdg.com

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Interesting, thanks Robert.I researched this a bit more, and it seems that the FAA RNP-certifies particular avionics systems.For example, the following Boeing aircraft are RNP certified (with specific versions of FMC software installed):737, 747-400, 757, 767, 777, 717, MD90, MD10, MD11


- William Ruppel, CYKF, VATSIM 816871

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The Bendix manual actually states that the system is not certified for RNAV (GPS) navigation or approaches. That pretty much rules out RNP capabilities.


Dan Downs KCRP

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Guest realatp
The Bendix manual actually states that the system is not certified for RNAV (GPS) navigation or approaches. That pretty much rules out RNP capabilities.
Ok so if it's not certified for RNAV nav then what the hell is it for?

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There wasn't much RNAV when this product was introduced, in fact I bet that there were no RNAV SIDs/STARs at that time. It's pretty good and navigating a VOR-based flightplan.


Dan Downs KCRP

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Ok so if it's not certified for RNAV nav then what the hell is it for?
I would be really surprised if it was not at least certified for RNAV VOR/DME, say enroute only. RNAV is NOT synonymous with GPS as some seem to imply here, lets remember that. There were many RNAV-certified units before GPS was even invented, before J41 even flew first time.

Michael J.

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Gents-(Tim: Language. Warning. 'nuf said.)When this airplane was put in service, RNAV was still called "Future Navigation."The FMS in the J41 can be used as your primary source of navigation enroute. It can also be used for lateral navigation on SID/STARs.What it cannot be used for is approaches, because it does not have the processing/computational integrity required to do vertical profile computations.In other words- you can use it as your primary source of navigation from takeoff until approach.To do so- you must have a secondary source of navigation information available for cross referencing.


Robert S. Randazzo coolcap.gif

PLEASE NOTE THAT PMDG HAS DEPARTED AVSIM

You can find us at:  http://forum.pmdg.com

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Not really sure what Captain Bob means when he says the JS41 can't be used for "Approaches". I flew into Duluth (KDLH) Rwy 27 via the (Dayar) IAF DME ARC to the ILS ... all completely handled by the FMC. All I had to worry about was the speed and minimum altitudes. The ARC comes up on the FMC as an Approach option ... Ken Park


Ken Park

One day I'll make a good landing even if it kills me!

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The ARC comes up on the FMC as an Approach option ...
Ken,ARC is not an approach, it is only an initial segment of the approach. You flew an ILS approach here which really is handled outside of this FMC (you don't need FMC to fly one). Captain RR was referring above to RNAV-based approaches which can't be flown with this (real life) FMC unit. For example you could not fly any of the following approaches to KDLH rwy 27:http://204.108.4.16/d-tpp/0911/00125R27.PDF

Michael J.

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I maybe wrong, but I thought you can use the FMS for the lateral navigation on such approaches, but not as automatic landing as the vertical is not included in the FMS. Or can you use the GPS waypoints only as reference but need to have either visual conditions or additional NDB/VOR/ILS available in IMR conditions?


Happy flying!
Alexander M. Metzger

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The device lacks the certification for IMC RNAV (GPS) or (RNP) approaches, having said that I have used an early handheld Garmin mounted on a yoke bracket as reference for gps-based approach but only in VMC conditions... even used it once when I lost HSI gyro on an ILS to provide track information but that was a very unusual situation and would never recommend it.In the MSFS simulation environment, the JS41 FMS will provide navigation on an approach but there's a big difference between the simulation and the technical characteristics of real world systems. For example, the Garmin 530 has 12 GPS channels submitted to a comparator and will flag on error. There's not a parallel in the sim world.


Dan Downs KCRP

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but I thought you can use the FMS for the lateral navigation on such approaches, but not as automatic landing as the vertical is not included in the FMS.
.. the LNAV approach in the KDLH example I attached above only requires lateral GPS navigation .. but you still can't fly it with this unit for following reasons: 1. approach not in database 2. no proper CDI sensitivity scaling. (automatic/vertical has really nothing to do here), .. these are more immediate practical reasons, 'non-certification' comes even later.

Michael J.

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Ken,ARC is not an approach, it is only an initial segment of the approach. You flew an ILS approach here which really is handled outside of this FMC (you don't need FMC to fly one). Captain RR was referring above to RNAV-based approaches which can't be flown with this (real life) FMC unit. For example you could not fly any of the following approaches to KDLH rwy 27:http://204.108.4.16/d-tpp/0911/00125R27.PDF
Michal,What do you make of the snagit I uploaded for the RNAV you mentioned for Rwy 27 into Duluth?Ken Park

Ken Park

One day I'll make a good landing even if it kills me!

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Ken,Go ahead and experiment with it. It is totally possible that this simulated unit's database has some RNAV approaches. The real question hinges on - can you really fly this approach since a mere presence of waypoints is not enough. IF you can observe proper change of CDI sensitivity: +/- 5 nm enroute, +/- 1 nm terminal and then finally +/- 0.3 nm approach then in fact you could fly it (regardless of its real-life counterpart) but I doubt it. Since in this simulated world you can easily slew aircraft left/right it should be relatively easy to find out.More on the subject of CDI scaling during GPS approaches here:http://www.terps.com/ifrr/jan97.pdfIn real world your unit would never show you approaches you can't fly. So for example if the unit was approach certified but wasn't WAAS it would only show you that LNAV is available to you, you would never see LPV or LNAV/VNAV for this airport.


Michael J.

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