Go Around - what did I do wrong?

[Holger]

Hi Mark,

wow, thank you very much for your explainations and the wonderful video. Unfortunately, I am away from my PC until next week, so I cannot reproduce the approach by myself. But I am looking forward to do this. 🙂

Best regards,
Holger

[Holger]

Hi,

does anybody manage to fly an RNAV Approach with the latest build? Having everything correctly configured (I believe), I am unable to set the beast into Profile Mode at Platform Altitude. To be precise: I am descending to Platform Altitude via Profile Mode or LVL CHG, level off, hit "FPA 3.0" (or whatever the button is called in the FMC) so that  "V/DEV" in the Nav Display. I am several feet below the desired glidepath in ALT HLD mode and as it is slowly approaching to my altitude, I hit PROF - but nothing happens. The button does not illuminate and the AT does not decelerate.

Doing the same in the A310 works perfectly everytime.

Best,
Holger

[Crabby]

55 minutes ago, Holger said:

Hi,

does anybody manage to fly an RNAV Approach with the latest build? Having everything correctly configured (I believe), I am unable to set the beast into Profile Mode at Platform Altitude. To be precise: I am descending to Platform Altitude via Profile Mode or LVL CHG, level off, hit "FPA 3.0" (or whatever the button is called in the FMC) so that  "V/DEV" in the Nav Display. I am several feet below the desired glidepath in ALT HLD mode and as it is slowly approaching to my altitude, I hit PROF - but nothing happens. The button does not illuminate and the AT does not decelerate.

Doing the same in the A310 works perfectly everytime.

Best,
Holger

I fly them all the time.  Are you sure you are at the platform altitude and NOT in Profile mode of any kind?  You must be on ALT HOLD or in LVL Change.  On the FMC did you see the FPA 3.0 change to some figure above or below the glide?  

[Holger]

13 hours ago, Crabby said:

Are you sure you are at the platform altitude and NOT in Profile mode of any kind?  You must be on ALT HOLD or in LVL Change.  On the FMC did you see the FPA 3.0 change to some figure above or below the glide? 

Hi Mark,

yes, everything you write is my procedure. Descending to Platfrom Altitude in LVL CHG, ALT HLD @ Platform Altitude, hitting FPA 3.0 so that a deviation in feet is being displayed. The appropriate graph is shown on the ND... I am waiting for it to come close to my ALT and then I try to hit PROF but the plane does nothing. At least I have to fly the RNAV approach manually. 

And all that works in the A310.

Regards from Munich,
Holger

[Azlog]

36 minutes ago, Holger said:

Hi Mark,

yes, everything you write is my procedure. Descending to Platfrom Altitude in LVL CHG, ALT HLD @ Platform Altitude, hitting FPA 3.0 so that a deviation in feet is being displayed. The appropriate graph is shown on the ND... I am waiting for it to come close to my ALT and then I try to hit PROF but the plane does nothing. At least I have to fly the RNAV approach manually. 

And all that works in the A310.

Regards from Munich,
Holger

I find you need to be level in ALT HLD mode at the altitude shown at the start of the RNAV approach on the chart with the altitude set to that height. You then press Profile and PDES comes up in blue on the PFD under ALT and turns green when VDEV approaches 0. I have occasionally had to descend to the final fix altitude on level change mode and try again

[Holger]

Hello everyone,

please join me on a very short test flight from Linz to Salzburg.

Today's route is LOWL Rwy 08 LIDSI1E LIDSI DCT MATIG MATIG2R LOWS Rwy 15

Here we are sitting at the apron of Linz and I am just going through the checklists and feed the FMC.

 

A few moments later I am taking off - although I am carrying no cargo for this flight, quite late due to the T/O-thrust bug. But never mind...

 

It is indeed a very short flight - our Cruising Altitude is just FL120. We have left Linz to the east and after a 180° turn over the city we are already heading westwards.

 

Great weather today! Almost spring here...

 

Here comes the interesting part: MDA is entered with 1.611 ft. WS832 and SBG are the last waypoint on the STAR. They have to be crossed at 5.000 ft or above. Platform Altitude is 4.000 ft.

 

But since WS832 is the IAF, I have chosen to cross it at exactly 5.000 ft. And as you can see, I am BEFORE the IAF and I am NOT in Profile Mode.

 

A few moments later, I have entered the Platform Altitude and the plane has turned into final approach. At Platform Altitude, I hit PROFILE mode several times, but the button never turned green. There was also no blue P.DES ARMED info on the PFD. However, to my big surprise, the light on ALT HLD turned off, P.DES was shown on the PFD and the plane started to descend by magic. I did not expect that!

During my last flights, I have always turned off the AP did the approach manually, since I had no info from the plane that it will carry out the RNAV approach.

 

During the final phase of the flight, things got crazy: The computed approach speed was very low (only 118 KIAS), so that I wanted to manually enter 130 KIAS. As mentioned in the videos earlier in the thread, it should be possible to fly the RNAV approach with a dedicated airspeed. But when I touched the knob, the AT turned off and the engines spooled up like crazy. I had to turn off the AP and fly manually in order to get stabilized again.

 

Short final...

 

...and a more or less perfect landing on this scenic airport.

 

So...  - the remaining question is: WHY doesn't the plane tell me that it is carrying out the RNAV approach? Why is the PROFILE button not illuminated? Why don't I get an "armed" message on the PFD as soon as I hit the 3° FPA button?

 

Best regards,
Holger

[Crabby]

1 hour ago, Holger said:

So...  - the remaining question is: WHY doesn't the plane tell me that it is carrying out the RNAV approach? Why is the PROFILE button not illuminated? Why don't I get an "armed" message on the PFD as soon as I hit the 3° FPA button?

 

Best regards,
Holger

Not sure about some things, but you would not get an armed message on the PFD when you hit the Final 3.0 FPA button.  I hit that before I hit the Profile button to get the Prof Des message in the PFD.  I believe this is where things are going sideways.  

[Azlog]

So normally I would get to the 4000ft and make sure I was in alt hold mode. Then I’d go to the approach page, make sure I had entered the MDA and press the final 3.0 button on bottom right.

I’d then go back up to the autopilot panel and press the profile button. This should cause PDES to appear in blue under ALT. The lights on the autopilot panel won’t change

Prior to reaching the WS816 waypoint, I would ensure that the aircraft is fully configured with gear down and flaps fully extended, otherwise it won’t do the RNAV approach

When the VDEV in the approach page hits 0, the light on the alt hold button goes out (you’ll hear a click) and ALT on the PFD is replaced with a green PDES. The light on the profile button will not come on at any point during this.

The aircraft will then descend on the glide slope at speeds dictated by what is entered in on the approach page which you can add wind correction to if you want a little faster. You can’t adjust the speed on the autopilot panel as this will take it out of “profile mode” and initiate a go around

[Azlog]

I feel that it’s also worth mentioning that the speed it gives you should be the speed you should use unless the headwind component exceeds 10kts (in which case, add half the headwind component minus 5. So 16kt headwind, add 3) or it is gusty (in which case, half of headwind before and all of gust. So 16kt headwind gusting to 20kt you would add 7) but no more than 15kt addition I think it is.

The reason for the speed it gives is to allow the aircraft to sink gently down onto the runway when you reach 5ft after idling the throttles at 20ft or so. If you come in too fast, you’ll just float down the runway and touch down far too late and/or hit it hard

[Holger]

Hi all,

thank you very much for your valued input. 👍

7 hours ago, Crabby said:

I hit that before I hit the Profile button to get the Prof Des message in the PFD.  I believe this is where things are going sideways.  

Yes, that's what I did, too. In the A310, I get a blue P.DES message on the PFD notifying me that RNAV is armed.

 

7 hours ago, Azlog said:

So normally I would get to the 4000ft and make sure I was in alt hold mode. Then I’d go to the approach page, make sure I had entered the MDA and press the final 3.0 button on bottom right.

I’d then go back up to the autopilot panel and press the profile button. This should cause PDES to appear in blue under ALT.

That's what I mean.

 

7 hours ago, Azlog said:

The lights on the autopilot panel won’t change

Ah, I see... However, this is a weird Airbus logic back these days. It's hard to understand why the PROF button does not turn green, since ALT HLD, LVL CHG and PROF are always somehow illuminated during the flight - depending on which mode is active. But in this crucial situation the pilot does not know about it. Especially in my case, when I do not get a blue P.DES message.

 

7 hours ago, Azlog said:

The light on the profile button will not come on at any point during this.

Thank you for the confirmation.

 

I believe Mark is right and there is a mistake in the order I press the FPA and PROF button in this situation.

 

7 hours ago, Azlog said:

Prior to reaching the WS816 waypoint, I would ensure that the aircraft is fully configured with gear down and flaps fully extended, otherwise it won’t do the RNAV approach

Oh, that might become a problem with ATC seperation on long finals. In Salzburg it is 8 NM, but there are also airports with longer distances (from the FAF to touch down). Following what I have learned for ILS approaches, I have to be fully configured at about 6 NM and stabilized at least at 4 NM.

 

7 hours ago, Azlog said:

The aircraft will then descend on the glide slope at speeds dictated by what is entered in on the approach page which you can add wind correction to if you want a little faster.

Hmmm... You should be able to fly the RNAV approach even with manual thrust. See the first video in this thread (although this relies on the A310, but I believe it is the same on the A300).

 

I just read that a new version of the A300 is out. I did not read the changelog yet, but I will try to do some training in the evening when the kids are in bed. I need to become more confident with RNAV approaches. Since they are a mix of automated and manual flying (the last few miles), they are my prefered approach type for bigger aircraft.

 

Again, thank you!

 

Best,
Holger

[Azlog]

Yeah I’m not quite sure how it is done in real life as normally on an ILS you’d want 180kts at more than 8 miles out, 160kts between 8 and 4 miles out and then final approach speed at less than 4 miles out but RNAV doesn’t really allow for that. Or at least not in the A300/A310. In the A320 RNAV works the same as ILS in that you just press the approach button and don’t think it matters if not fully configured

 

Could be the order you are doing it. I always think level hold, final 3.0, profile and it works almost every time. Had a couple where I’ve had interpreted the chart wrongly and had to descend further before trying again but it always gets there eventually. Since getting the A300, I’ve been doing quite a few cargo ops routes in the US which involves a lot of airports with RNAV approaches

 

You probably could disengage auto throttle and it might still work manually. I’ve never tried it as I normally keep auto throttle on until around 400ft to avoid chasing around trying to find where the throttle was set which can very quickly destabilise the approach

[Holger]

Both, the A300 and A310 are great addons as they are far away from the 737/A320 mainstream. And they offer a great challenge if you want to operate them as close to reality as possible. The A300 still has some issues, but I like it nevertheless. Last week I flew from Cologne to Kuwait City. And instead of flying back to Central Europe, I continued via New Delhi, Kathmandu, Tokyo, Seattle, Atlanta, Nassau, New York, East Midlands further eastwards. Pretending to be a freight dog offers you plenty of new destinations in FS.   🙂