Pmdg 737 Rnav

[Brett Mcgalliard]

HiEveryone: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

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

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: _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).

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 were 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 arent, but I think they could still fly an Rnav RNP approach as long as the RNP is met. Its 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 Ive 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 wasnt inhibited by the crew. I dont 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

So, is this right? My understanding is that what gives vertical nav capabilities is the AFDSs 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?

the A300 has become my favourite plane at the moment. Today, I was flying into Nantes Atlantique LFRS, RW21. This RWY has an RNAV approach. During the final phase of this flight, I was turning into Final Approach and I was flying according to the requirements given by Approach Chart. AP was active, I have activated "Land" and "Approach", so that "CAT2" was shown on the PFD.

So, I thought that RNAV would be active - but the plane did not sink below 3000ft (which was the dialed in altitude). This led me to do a manual approach, but since the weather was quite heavy (40 knots wind on the nose, heavy rain), I had to do a go around.

I wanted to do a 2nd attempt, but I was unable to insert LFRS as a destination into the FMC again. Instead, LFPG was shown as the alternate airport. So, I have manually entered the waypoints and constraints of the new STAR until the FAF. When I have reached FAF, I was unable to to make an autoland, because I got the "Discontinuity" message and AP disengaged. I was unable to tell the FMC that I wanted to land at LFRS RWY21. Any attempts to insert LFRS in the "Fight Discontinuity" line failed as well as adding "LFRS" as a new waypoint behind the FAF.

LFRS RW21 has no ILS, only RW 03. You may tune the ILS, you will get the CAT category of the ILS, but there are no LOC and GS to guide the AP. So the only way for auto apr to minimums is the RNAV apr. To follow the VNAV path for the RNAV apr in the A300 is not the same with modern a/c. You must enter the DH in the MCDU and the a/c will make the required degrees decent after reaching the FAF. See the video tutorials (RNAV apr) for the exact procedure required.

Just for my understanding (because it does not make sense to me): I am descending in PROF mode to the platform altitude (e.g. 3.000 ft). MDA and DH is set properly, AT is active. Then I need to leave PROF mode and change to ALT HLD (or whatever) and enter PROF mode again? Hmmm...

Where is the descent angle shown? I did not see it yet.

Another thing that bugs me is that neither the A300 or the A310 are following constraints properly. E.g. I have set ALT to 4.000 ft, but a waypoint close to me has 3.000 ft mandatory. I expect the plane to stop at 3.000 ft until passing this waypoint before climbing to 4.000 ft. Or are those old planes not capable to follow this logic?

@Holger i have to apologize, you seem to be right. I didnt manage to fly an rnav too. The only way i got the plane to descend from the FAF was dis- and reengaging Profile mode. Which doesnt feel right, does it. MDA had been entered correctly. I think i will make a video of this, maybe i dont understand the system correctly...

3a8082e126