Ray, Read up on FCTM->Approach and Missed Approach->Non-ILS Instrument Approaches. There is some information there about "coded vertical angles". Basically, the VNAV will dive and drive until the FAF, and from there, it will descend at a given angle. However, if you put in hard altitude constraints, VNAV will perform a "geometric" descent, that is, descend at an appropriate angle to meet both restrictions without levelling off."torkermax", RNAV/RNP/GPS approaches are "non-precision approaches". All this means is that there is no vertical guidance. Anything in the aircraft that looks like vertical guidance is generated purely by the system. When you descend with VNAV or IAN, it is the same as descending at ~750 fpm in V/S and crosschecking your altitude vs. distance every mile, except much easier. I doubt airliners will ever use WAAS as it is only wide-spread in the US because of the abundance of smaller aerodromes. WAAS is a cheaper solution to provide low minimums to all of these aerodromes as it covers a large area. The international community (incl. US) is looking at LAAS/GBAS for CAT I or even CAT II/III minimums because these are more likely to be deployed to larger aerodromes where ILS already exists and they are looking for an alternative solution.

You can shoot RNAV, GPS and RNP approaches down to LNAV/VNAV minimum.Also, GLS = GBAS = LAAS, but this is not available in the NGX.

Hi David, I'm guessing you are referring to the simulator For the others, for your information - Qantas (2007 Article)RegardsJay Cargo

Well what is the NGX other than a simulator? ;)

Hi David,Ya, have read that page as well, but I still don't think the acft guarantees a constant angle to the next point, it might do a 'concave' though. Only the vertical path angle coded in the db, and only to the MAP or E/D (aka runway) will ensure a constant angle. Besides, NGx doesn't allow consecutive angles as opposed to arinc424 rules where multiple segment can be programmed. I guess that's just an industry FMS/ARINC harmonization issue.Tks

Well what is the NGX other than a simulator? ;)

Lol..sorry thought you were referring to the aircraft regards

Arming the APR button tells the FD to capture the Glide Slope in case of an ILS and Glide Path for a RNAV approach such as a LPV. If flying on line, arm the approach when cleared for the approach as the clearance is your permission to descend from from the initial approach altitiude.

Hi,I find this subject interesting so I would just like to contribute what I read, although the topic is abt shud one press the APP on an Rnav.A couple of things: (one not related to another)1. I am not sure if Lnav/vnav will maintain the gradient as the acft is on idle thrust descent. It might 'dive/drive' if the wpt constraints are a little far apart. I wud rather use NGX new vertical path function while I 'monitor' the alt-constraints/dme, it is non-precision anyway.2. FMSs with multi-mode recvrs such as the rockwell collins GLU-925 are able to fly GLS. Qantas has been doing this since 2005 on trial with Oz's GBAS system. You select the coded GLS procedure and the 5 digit 'frequency' will correspond a runway GLS 4-letter code in the approach ref page, also in the PFD. A different model NAV panel is also required to enter the 5 digit 'freq'.3. I'm sure u will need GPS on such approaches as it wud hv been mentioned in the notes on the plate. However, if you are using a micro-IRS with a hybrid GPS (with many kalman filters algorithms), there is an available 'coasting time' when u loose GPS, for various RNP-AR such as RNP 0.3 ~25mins (most limiting) ... refer to Honeywell Laseref V product.Just found it useful to add to our knowledge.Ray

Does Pressing APP actually "Override" the LNAV/VNAV buttons I have pressed? In other words, when pressing APP, it seems you are all saying that the FD will direct the plane down the Glide Slope as it were an ILS approach (even though this is technically a non precision approach). But does the APP button actually override the LNAV/VNAV way of doing the approach? In short, what is the difference if I just leave it with the LNAV/VNAV buttons pressed? Will the aircraft do exactly the same thing whether I press or don't press APP? Will the representation change on my PFD if I press APP? Is that the only difference? Or does the plane actually FLY the approach differently with LNAV/VNAV as opposed to APP? Again, is APP actually overriding the LNAV/VNAV buttons to fly the approach in a slightly different manner?Sorry to beat the dead horse... I am still a little confused.Thanks,Chris Catalano

Does Pressing APP actually "Override" the LNAV/VNAV buttons I have pressed? In other words, when pressing APP, it seems you are all saying that the FD will direct the plane down the Glide Slope as it were an ILS approach (even though this is technically a non precision approach). But does the APP button actually override the LNAV/VNAV way of doing the approach? In short, what is the difference if I just leave it with the LNAV/VNAV buttons pressed? Will the aircraft do exactly the same thing whether I press or don't press APP? Will the representation change on my PFD if I press APP? Is that the only difference? Or does the plane actually FLY the approach differently with LNAV/VNAV as opposed to APP? Again, is APP actually overriding the LNAV/VNAV buttons to fly the approach in a slightly different manner?Sorry to beat the dead horse... I am still a little confused.Thanks,Chris Catalano

It won´t overide your lanv/vnav. It will display information for you in a different manner though, similar to the ILS needles. So to answer your questiom: no, it won´t disarm lnav/vnav, but the FMA will shoe G/P and FAC instead of the usual lnav/vnav annunciations. And yes, it will change the way informatio is displayed in the PFD. You will see needles.

Will the aircraft do exactly the same thing whether I press or don't press APP?

No, it will NOT do exactly the same.APP is actually a very important information for the flight control software since it knows it is arriving at some point (MAP, etc) and must tighten the vertical/horizontal tolerances as if it was riding down a cone-shaped ILS beam. So yes, unless you press APP you usually will not get the same thing, also it would be a reason to disqualify you as a pilot during an IFR check ride.

Michael, you will find that not all aircraft have IAN and in fact, most commercial airliners around the world will do NPAs using LNAV/VNAV. You will notice that even en route, the aircraft normally has a cross-track error of less that 0.03NM. When tracking a straight line, it often wavers between 0.00NM and 0.01NM. I would hope that this is close enough - I doubt you would achieve better results hand-flying.The FMC actually enters an "Approach" mode once certain conditions are met anyway... these are in the FCTM.Differences between IAN and LNAV/VNAV... - In IAN, Vertical and lateral deviation shown on PFD as "ILS"-like diamond pointers - In IAN, No need to dial the MCP ALT to the MDA at commencement of approach - IAN does not suppose curved approaches, so fancy RF-leg based approaches must be done in LNAV/VNAV.

These terms can be very confusing, and sometimes overlapping.WAAS is used for general aviation for GPS-based approaches called LPV, like someone said earlier. Unlike GA, an NG does not use the WAAS to turn the usual non-precision GPS approaches into LPV approaches.What we´re seeing today is the implementation of a system similar to WAAS for civil aviation. It is called GBAS (Ground Based Augmentation System) and with it a new type of GPS-based precision approach will be made available: The GLS approaches (GPS Landing System). The GLS approaches will be to civil aviation what LPV is for GA. What we currently have for NGs is Rnav GPS approaches which are non-precision. We also have, like you mentioned Rnav RNP approaches with lower minimums.The way I see it (and I could be wrong here), an NG can fly an Rnav GPS approach if it is equipped with GPS. Some aren´t, but I think they could still fly an Rnav RNP approach as long as the RNP is met. It´s just a matter of nomenclature and equipment being used to guide the AFDS. But to stay below an RNP of 0.3 or 0.15 without a GPS, the acft would have to be flying somewhere with many VORs/DMEs available for radio-updating, I believe. So in theory you could have an acft not be qualified to fly an Rnav GPS approach but fly the same procedure were it to be named Rnav RNP approach. And I´ve seen tons of GPS and RNP plates that are nearly identical, only minimums differing between them.Since all of these navigation systems (IRS, GPS, VORs/DMEs and Locs) are weighed against each other in a complex mathematical formula to give out the calculated FMC position, I have a hard time knowing when the GPS is actually being used to fly GPS or RNP approaches. My guess is always, as long as GPS updating wasn´t inhibited by the crew. I don´t know if in theory an RNP 0.15 approach can be flown without having GPS aboard. Depending on where you are, your ANP can exceed the RNP and result in a missed approach.With GLS things will change greatly. You will still use Lnav/Vnav to fly a GPS-based approach, but the minima will be way lower, similar to LPV and lower than RNP0.15Rick, you seem to know your stuff, so I have a question for you. Like I said above, isn´t LPV restricted to WAAS-enabled general and business aviation acft? I don´t know of any Boeing acft with such systems. But a friend of mine who is a capt for GOL said their new NGs are rolling off the factory with GBAS receivers, allowing for GLS.

Actually, for a nominal fee you can equip any aircraft with WAAS or GBAS systems. You have to pay for the MOD and have the aircraft certified with the MOD. You are right, mostly general and business aircraft use WAAS systems that the LPV is based on. Some aircraft can only use WAAS for lateral while some have the capability to use it for vertical also.

Hi,I find this subject interesting so I would just like to contribute what I read, although the topic is abt shud one press the APP on an Rnav.A couple of things: (one not related to another)1. I am not sure if Lnav/vnav will maintain the gradient as the acft is on idle thrust descent. It might 'dive/drive' if the wpt constraints are a little far apart. I wud rather use NGX new vertical path function while I 'monitor' the alt-constraints/dme, it is non-precision anyway.2. FMSs with multi-mode recvrs such as the rockwell collins GLU-925 are able to fly GLS. Qantas has been doing this since 2005 on trial with Oz's GBAS system. You select the coded GLS procedure and the 5 digit 'frequency' will correspond a runway GLS 4-letter code in the approach ref page, also in the PFD. A different model NAV panel is also required to enter the 5 digit 'freq'.3. I'm sure u will need GPS on such approaches as it wud hv been mentioned in the notes on the plate. However, if you are using a micro-IRS with a hybrid GPS (with many kalman filters algorithms), there is an available 'coasting time' when u loose GPS, for various RNP-AR such as RNP 0.3 ~25mins (most limiting) ... refer to Honeywell Laseref V product.Just found it useful to add to our knowledge.Ray

If your FMS has the RNAV approach in the data base, it will meet the altitude constraints while in LNAV/VNAV. The FAA and other authorities are moving away from the old dive and drive for caculated constant descents. This ensures you stay with in the terps regime during the approach. VNAV makes this easy. The dc10s i flew had GPS but did not have the ability to couple to the V path. We had a indicated path that you used as a target but the aircraft was not certified for vnav ops. The added certification to the G550 to use APP for RNAV/non precision approaches brought on a nice change. This gives me the ability to set my missed approach altitude in the altitude window after capturing the FMS glide path. One less thing we have to worry about during the missed approach. If i fly a GPS or FMS approach, the aircraft will fly down the path meeting the altitudes until i disconnect and land or go around. In the G5 i have to progressively set altitudes along the way to mins. If i go missed, it's a mad dash to configure, set speed modes and ensure the missed approach alt is set as the jet climbs away quickly like a rocket.

Wish we had video tutorials on this stuff.AOA where are you?

A summary for all those who are confused by the lengthly discussion:WAAS(US)/ EGNOS(Europe)/ GAGAN(India)/ MSAS(japan) are all SBAS (space based augmentation systems), augmenting the GPS signals the acft receives. This makes it more accurate. IRS coasting is allowed on RNP-AR approaches depending on certification, of course FDE predictive checks ought to be done prior to operation.LPV minimums are approaches where the aerodrome has GBAS (ground augmentation) and the acft must be capable of receiving these signals transmitted via VHF to the unit onboard to define the non-linear ILS type guidance. Europe is already seeing quite a few in Switz, France etc.

It's your choice. Just using LNAV will give you higher minimums and you manage the guidance system to meet altitude restrictions during the approach. LNAV/VNAV will get you lower and the aircraft guidance system will give you vertical and lateral guidance ensuring you meet the altitude restrictions. Selecting the APP mode during the RNAV approach will put you in IAN mode which allows LPV minimums if your aircraft is capable. This mode operates like an ILS, very useful if you are shooting the LPV. Every RNAV approach will not have LPV minimums. The mode you use is driven by the equipment and capability that your aircraft has. It's all driven by the navigational performance of the aircraft. Take a look at the RNAV(GPS)Y RWY 16 at KHPN. Lets look at CAT C for the different modes. LNAV brings you down to 621ft agl with the weather at 700ft with vis at 1.75 miles. LNAV/VNAV gets you down to 539ft agl at 600ft at 1.5 miles. LPV brings you down to 250ft agl at 300ft and .5 miles. So if i was doing the LNAV with the ceiling at 300ft and vis at .5 miles, I'm out to lunch. The LPV would get me in if my aircraft was capable. In my ops, we add 50ft to the minimums because my aircraft will dip an extra 50ft during the go around. This prevents you from diping below mins. All based on the FAA tests done for altitude loss during go-arounds.

Thank you for this.

Very many thanks to EVERYONE participating in this thread.I have learnt much, from the questions and the answers - great stuff!The BRILLIANT NGX, combined with the outstanding knowledge base in this forum, is just fantstic!Thanks!

Thank you for this.

I posted a guide for approaches in the forum. it contains a rnav, and a fms non-precision app to a circle. Great guide for setting mins. Do a quick search or search my name. I will do a non fms non-precision next. A dme arc type.