Hi Everyone:I am confused about something - if I am flying an RNAV Approach and have VNAV and LNAV enabled (and have dialed down the lower altitudes I need), is it necessary to hit the APP approach button as well? Will this even do anything? Or if I don'thit the APP button with LNAV and VNAV enabled, will the aircraft automatically begin to fly down the glideslope when it hits the Final Approach Fix as expected? (like doing an ILS approach)Thanks,Chris Catalano

Use Lnav all the way to destination - then 10 miles on final hit Loc at 2,000agl - 8 miles out hit App - make sure ils is in nav 1 thats it I never use vnav, thats just me.

He's asking about RNAV (gps) approaches, not ILS approaches.

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.

So does that mean if I don't arm the approach in an RNAV approach that the Glide Path will not be captured, even if I am using LNAV and VNAV together? In short, do I need to arm Approach under any circumstance?Thanks,Chris Catalano

So does that mean if I don't arm the approach in an RNAV approach that the Glide Path will not be captured, even if I am using LNAV and VNAV together? In short, do I need to arm Approach under any circumstance?Thanks,Chris Catalano

No you dont need to arm APP. (RNAV dont use ILS freq so APP will do nothing).

There are two (well, actually three, but V/S is not normally used for approaches in the database) ways of executing a non-precision approach (NPA) in the 737NG.IANIAN or Integrated Approach Navigation is a customer option. Basically what it does, is make NPAs look like ILS approaches. To use IAN, all you have to do is select the approach from the database, and hit APP before you reach the FAF. This is not available for curved (RF) approaches.VNAVOn aircraft without IAN, VNAV is the preferred method of shooting NPAs. When cleared for the approach and inside the IAF, set the MCP ALT to the MDA, rounded up to the nearest hundred. Once inside the FAF and more than 300FT below the missed approach altitude, set the missed approach altitude. The aircraft will continue descending in VNAV PTH. You should engage VNAV no later than the FAF. For approaches using LNAV for guidance (mandatory for GPS/GNSS/RNP/RNP-AR approaches), you should have LNAV engaged any time you are suppose to be tracking on the approach.In any NPA, you should set your minimum bug to MDA + 50FT or the LNAV/VNAV DA. The 50FT buffer added to the MDA is there to reduce the chance of descending through the MDA in case of a go-around.More info is in the FCTM -> Approach and Missed Approach -> Non-ILS Instrument Approaches, as well as this Boeing article: http://www.boeing.com/commercial/aeromagazine/aero_22/737approach_story.htmlAll features in that article are modelled as options in the NGX, except for GLS (which, as far as I am aware, is not approved for use in IMC in any part of the world at this time).

Hi Everyone:I am confused about something - if I am flying an RNAV Approach and have VNAV and LNAV enabled (and have dialed down the lower altitudes I need), is it necessary to hit the APP approach button as well? Will this even do anything? Or if I don'thit the APP button with LNAV and VNAV enabled, will the aircraft automatically begin to fly down the glideslope when it hits the Final Approach Fix as expected? (like doing an ILS approach)Thanks,Chris Catalano

Yes yo need to press APP on the MCP for a RNAV approach. Have a look at this post and just follow the process, it's very clear :http://forum.avsim.net/topic/353105-ian-approach-krno/page__fromsearch__1There are more information in the FCTM.pdfRegards,Richard Portier

David and Richard said it all. In simpler terms, pressing app when flying a non precision approach (such as rnav) will generate a glidepath that the autopilot will follow just like it would an ILS-derived glideslope. That is the principle behind IAN. It makes flying these approaches simpler and more intuitive, similar to what pilots are used to all over the world: ILS

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.

Do you actually fly RNAV GPS approaches in an NG or do you fly RNAV RNPs. I admit I tend to only fly an RNAV approach is I have the chart and it is RNP. I just never saw any indicators that dictate that I can fly GPS approaches in an NG, I thought those are WAAS.

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 RNP0.15

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.

Rick, 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.

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.

So, is this right? My understanding is that what gives vertical nav capabilities is the AFDS´s Vnav. GBAS (which really is the same as LAAS, like David pointed out) and WAAS are different systems, based on the same principle, with similar net results: to greatly enhance the navigational accuracy of the GNSS and to maintain the integrity of the system, letting the user know when accuracy becomes degraded. GA in the US has been using WAAS for some years now and several Rnav approaches throughout the country have LPV minima. LPV is a "sub-type" of GPS approach wih precision approach-like (i.e ILS) minima. And you get that thanks to WAAS.GLS, based on GBAS(LAAS) will do the same for airliners, correct?

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