Auto-coupled RNAV approach setup
I cannot seem to find a definite step by step procedure to allow autocoupling on RNAV approaches. I watched it being performed on Youtube but I could not see nor was it explained what they were setting up in the FMS. I understand that the lower left box on the radio panel has to be set to FMS and at some point APR armed must be selected from the NAV page but something was said about setting up and capturing VNAV first and then it would automatically disconnect or something. That part didn't make sense. At some point APR ACTIVATE has to be selected from the FMS NAV page but don't know when that is to be sequenced. I saw that the upper left of the PFD showed LNAV APR when it was all working but I am not able to get it to autocouple. I can fly LNAV/VNAV but the AP will not autmatically follow the virtual glideslope for me. In short, I need someone more knowledgeable to give me a "step by step". Thanks in advance.
Craig
Comments
Actually Craig I'm just about to record a video for my channel on this very subject. Basically, you must first of all check the ANP in the NAV page of the FMS, and keep an eye on it throughout the descent and approach where possible to make sure it doesn't go above 0.3NM, and set that as an aide memoire in the RNP section of the NAV page.
Make sure both the lateral and vertical trajectory in the FMS is exactly as stipulated on the approach chart during your descent preparation, and the missed approach procedure too.
You'll be cleared to the IAF (never the FAF) of the approach, which should be at least 2 miles from the FAF. Once this occurs, arm the approach in the NAV page of the FMS.
LNAV then turns to LNAV Approach mode on the FMA. Once the vertical deviation appears on the PFD, select VNAV and you should then see VNAV PATH on the FMA.
Make sure you dial in the decision altitude of the approach on the altitude selector
because during my testing, I've found that if you select go-around altitude as you would
on capturing the glideslope of an ILS approach, the aircraft sometimes won't go down.
This just means that if you do need to go around, you'll have to set the go-around altitude as well as doing all the other things that need to be done. Also make sure
ALT SEL isn't selected as it usually would be - we don't want the aircraft to level us off
as decision altitude, or at any other stage during the approach.
That's pretty much it - if I'm wrong, I'm sure others will correct me, but as I said, I'm just
about to record a video for my channel on the topic and that may make things a little more comprehensible.
John
Thanks, John. I have been doing some experimenting. One major discovery is that it seems not to want to create a virtual glide path if any of the fixes in the approach have been altered from what is in its current Q400 datebase. I use charts that match the scenery I have in FSX. So I occasionally find that the fixes being used in the current update database do not match my airports since they are frozen in time. With other aircraft, they will fly whatever I input in the flight plan. Indeed so will Q400 but not when it comes to approach. Also there are some VOR/NDB stations that have been decommissioned and therefore no longer recognized by Q400 even though they are still operational in FSX. It is indeed rather fussy, isn't it?
Since my post, I have had two successful RNAV approaches and both times the LNAV APR mode disregarded my set altitude and tracked the virtual glide path. According to what I have gleaned from others, the procedure seemed to be to keep the IAF altitude set without need to set it to the MDA. After confirming the plane descending correctly down the path, the Miss Altitude could be set without disturbing the descent. But I am using FSX. If you are using PD3 things might act differently. One difference I note from your procedure is that it was recommended that the approach had to be set to "ACTIVE" in FMS once VNAV was alive on the PFD (within the 2 minute range). I did so on both of my flights. Could that account for the difference? My experience is still rather shaky when it comes to this approach. In the 737NG it is a common feature called IAN and can be used for almost all non-precision approaches. Great to find that the Q400 has that capability. It doesn't seem to work for other non-precision approaches though. Tried to make it work for VOR but no joy. (But then again I was using my own fixes for the approach.)
Craig
Craig you're absolutely right - when you put your own fixes into the routing, the Majestic Q400 just won't do it. I have no idea why and whether that's realistic or a bug within the sim.
Technically, if you're doing it with a VOR approach, that's an RNAV overlay approach and in real life you would need the VOR to be tuned and active as a backup, so trying to do the approach in the absence of the beacon wouldn't really work out.
John
I am learning! Q400 definitely has a distinct personality! Thanks for the response, John
Craig
Craig, just as an update, the UNIVERSAL FMS manual states that no segment of the approach generated by the FMS can be edited, or the FMS-based approach can no longer be flown as an FMS appraoch. It says also that you may have duplicate points, in which case, just leave them and do not delete them.
So, it's not a bug but a genuine, realistic feature of the UNIVERSAL FMS - you can't edit the points on an FMS-based approach and, if they're not correct, you have to revert to an old-fashioned radio aid approach.
John.
You're absolutely right. I discovered that yesterday by trial and error. You hit the nail on the head. I was deleting the duplicate waypoints because they didn't make sense. I have done the same with ILS approaches but because they are navaid dependent I have not had any issues. So I naturally assumed that I could do the same with the RNAV. When I left it untouched it worked like a champ! The issue still remains, however, that I do have older charts that have RNAV approaches using different waypoints and with other aircraft, I have just edited the FMS flightplan to correspond to the charts. But if it is basically the same approach using the Q400 rendition should work fine. Thanks for your excellent input.
Craig