Go-around performance issues

[badderjet 181]

I'm back in the sim on Thursday so I will try to get some video of the Coupled vs Non coupled G/A for comparison. What equipment type are you operating? (FP or FO)

If you can, please make your footage public. Looking forward to seeing it. If you can do multiple runs, you might want to shoot during single as well as dual channel operation.

That's because it is something of a VS mode. The VS you get depends on the flap angle you have set for the climbout (that's my understanding of the mode anyway). Try selecting less flap angle and you will get a higher VS. Target climb speed also increased with less flap angle.

That's contradictory to me. If it maintains V/S, you can't get a higher climb rate when retracting flaps. In fact that's what I'm doing, see above where I explained what it does for me. And BTW initial flap setting is fixed anyways - 15 or 1 for one engine out. During flap retraction target speed increases, but the system apparently tries to maintain around 1000 fpm climb rate, and does so by modulating thrust (and pitch of course). One of my original questions though was if it's intended to be a constant thrust setting in the first place (e. g. if there is "one" fixed reduced G/A thrust). Right now I see the thrust change all the time, so that confused me a bit. I just don't have a clue how it's supposed to be, but I figured it would be different.

[kevinh 409]

If you can, please make your footage public. Looking forward to seeing it. If you can do multiple runs, you might want to shoot during single as well as dual channel operation. That's contradictory to me. If it maintains V/S, you can't get a higher climb rate when retracting flaps. In fact that's what I'm doing, see above where I explained what it does for me. During flap retraction target speed increases, but the system apparently tries to maintain around 1000 fpm climb rate, and does so by modulating thrust (and pitch of course). One of my original questions though was if it's intended to be a constant thrust setting in the first place (e. g. if there is "one" fixed reduced G/A thrust). Right now I see the thrust change all the time, so that confused me a bit. I just don't have a clue how it's supposed to be, but I figured it would be different.

That's odd. I tried an auto go-around with different flap settings last night and it stabilised at higher speed and higher VS as flap was reduced. Maybe it's a weight effect? Like you I don't know how it's meant to work, so inputs from RW NG pilots are helpful. A lot depends on whether PMDG had access to the actual AFCS control laws or are trying to replicate what they observe the Level D sim doing. The later could lead to a situation where it works perfectly for one aircraft configuration but not so well for others. Kevin Hall

[zazaboeing 15]

Rafael, I'm back in the sim on Thursday so I will try to get some video of the Coupled vs Non coupled G/A for comparison. What equipment type are you operating? (FP or FO)

Hi Paul, I'm on the 737ng @ Gol as captain now.

[Spin737 102]

If you go-around from a dual-channel approach, the A/P stays on. If you're doing a single-channel, the A/P disconnects with the TOGA button. The speed window is closed and the commanded speed is based on flap position. Just clean up and don't worry about it. The window will open when a new mode is engaged (eg. ALT AQ).

[badderjet 181]

That's odd. I tried an auto go-around with different flap settings last night and it stabilised at higher speed and higher VS as flap was reduced.

Oh ok, just for me to reproduce - what was your approach flap setting and what did you select on the go-around, and were you all-engines or single engine?

Hi Paul, I'm on the 737ng @ Gol as captain now.

I think he meant if you were flying fail-op or fail-pass.

The speed window is closed and the commanded speed is based on flap position. Just clean up and don't worry about it. The window will open when a new mode is engaged (eg. ALT AQ).

That's interesting - but they positively have nothing to do with any other speeds usually selected, like flap maneuvering speeds, e. g. nothing like V_REF40+XX or so? As I mentioned before, they just 'look' odd to me, as if the system was just throwing random numbers of increasing order.

[Spin737 102]

That's interesting - but they positively have nothing to do with any other speeds usually selected, like flap maneuvering speeds, e. g. nothing like V_REF40+XX or so? As I mentioned before, they just 'look' odd to me, as if the system was just throwing random numbers of increasing order.

- F/D pitch commands 15° nose up until reaching programmed rate of climb. F/D pitch then commands target airspeed for each flap setting based on maximum takeoff weight calculations

That's all the systems handbook has to say about that. As many pilots like to say, "It's PFM" or Perfect Freakin' Magic. Translations may vary. In other words, you don't need to be able to build it to fly it.

[badderjet 181]

In other words, you don't need to be able to build it to fly it.

Weird, you're not the first one to tell me...

[nrcrate 40]

I'm sorry to disagree with you Paul,but the Non-Automatic (not a dual coupled AP) G/A in the NGX is completely erroneous compared to the real plane:- It disengages the A/P but it stays "ON in the background" and if you manually pitch up, it enters the CWS Mode for pitch and roll when you were flying F/D only! (that's ridiculous)- G/A power should remain sufficient to aprox. 2000ft/m and G/A Thrust Mode should remain on, not come back to cruise and reduce power when you need it the most- The second press should give you full thrust and STAY there, independent on any other mode, that's an autothrottle mode only! If you want get my help in beta-testing around these issues, I volunteer for that, no problem, just let me know.

EXACTLY!

[badderjet 181]

PS2 Ok now, as I understand it, letting the AP fly an ILS is pretty much independent from the FMS. In fact I could just dig up the chart, set up the radios, get my V_REF from the manual, set her on the localizer and go. No FMS involved at any point, and I don't think I'd have to select the approach on the DEP/ARR page either. Now try the following. Shoot the approach, and to be on the same side let's fly this as a coupled approach so let the APs do the work. At some point during the approach (earlier is probably better here), hit TOGA so as to "initiate" a go around, more importantly though to leave the ILS modes. Immediately cancel all warnings, gain manual control, kill AT and the APs and recycle the FDs. So your FMA should be clean and clear now. Also try not to leave the ILS too much. Now arm APP again. To my understanding, system wise we are at a point now that is no different from a usual ILS intercept (apart from that we're already spot on the LOC and G/S, more or less). However, I promise you won't get G/S armed in this state. You'll have to reselect the approach on the FMS, and then eventually it would let you arm G/S again. Remember, radios are totally unchanged, you still had your G/S indication, even around the center. And yet it won't arm.

Quoting myself for a second, as I found out the official conditions that should make G/S arm in any case: - ILS frequency select- AP or FD on- APP switch Nothing to do with FMS at all. These simple conditions should suffice for G/S to arm. As I explained, TOGA, then resetting AP will bust the system, and a reset is only possible by reselecting approach in FMS. Of course maybe there are other ways, but this is one way. And one that shouldn't be.

[kevinh 409]

Oh ok, just for me to reproduce - what was your approach flap setting and what did you select on the go-around, and were you all-engines or single engine?

I used Flap 30 and was on a dual coupled ILS approach, two engines operating, MCP altitude 4000 feet, heading select: runway heading. Selected go around at 200 feet RA, Flap 15 then gear up once the flap was moving. Once stable I tried various flap settings, increasing the selected altitude as necessary to prevent capture. I can't remember the exact weight, but I had about 6,000 LB of fuel on board and I hadn't changed the payload from the default start up setting, so ZFW about 121,000 LB. Kevin Hall

[badderjet 181]

Alright thanks, that should be enough to get me started.

[zazaboeing 15]

I think he meant if you were flying fail-op or fail-pass.

Sorry about that, it was fail passive.

[rocketfs 2]

My error. In re-reading FCOM, a miss-approach will NOT be automatic unless it is an autoland approach. I wrongly assumed that it would pitch up on its own due to the increase in power input but it makes sense that it would not sustain it without pilot input. The FD will indicate pitch but it must be input manually by pilot. If not the power will decrease to maintain the ASI setting. Seems the PMDG NGX may, in fact, be performing according to specs in the manual. My understanding then is that it will hold power setting as long as it is manually pitched up as commanded by FD. Full GA power would be available if necessary by a second TOGA press(?) I will try it on my next flight.

You initial post stated "coupled approach". That is autoland, not? Bert Van Bulck

[rocketfs 2]

Small addition to the previous, when you press the TO/GA button with an active approach, the aircraft will pitch up to establish a 1000-2000 FPM climb profile at VREF or MCP speed. Speed will increase as you retract flaps. If you want the throttles to advance to the Go Around thrust setting, you must press the button a second time or not have an active approach loaded.

Paul, A 1000 to 2000' climb: what will give 1000'/min and what will give 2000'/min? Bert Van Bulck

[badderjet 181]

A 1000 to 2000' climb: what will give 1000'/min and what will give 2000'/min?

Question I'm also having. Without manually intervening it will be too lazy to go past 1000 for me in any case.