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

Hi Bert! 'Coupled' uses autopilot vs 'manual' which does not. Dual Coupled would be required for full autoland.

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.

Sorry, but this is not correct, it does not work correctly in my setup. What should happen is that the autopilot pitches the aircraft up to follow the flight director which will be somewhere around 15 degrees nose up. This is to command a pitch setting which causes the aircraft to fly at the manoeuvring speed for the existing flap setting, which will be flap 15 for a two engine go-round. Except that the speed it actually flies at is as if it were at max weight with flap 15, not it's actual weight at that time. The autothrust will advance the thrust levers to provide sufficient N1 to achieve a rate of climb 1000-2000 FPM, the amount varies according to the conditions but is likely to be around 90%. When you reach acceleration altitude you retract the flaps on the speed schedule. Each time you reduce the flap setting the airspeed cursor will drive towards the manoeuvring speed for that flap setting although once again it assumes you are max weight so the cursor moves to a figure which is higher than the green mark on the airspeed tape. What actually happens is that you get a measly 78%, a pitch attitude around 7 degrees nose up & a ROC <1000 FPM. Cheers, Doug

What should happen is[...]Except that the speed it actually flies at is as if it were at max weight with flap 15, not it's actual weight at that time.[...]Each time you reduce the flap setting the airspeed cursor will drive towards the manoeuvring speed for that flap setting although once again it assumes you are max weight so the cursor moves to a figure which is higher than the green mark on the airspeed tape.

See my question regarding exactly this issue on the previous page. So this is how it should work? At least it's a good start for further investigation. As stated before, I have always been wondering about what weird speeds the system sets during flap retraction. Now it could make sense, but I'll have to check the numbers against the actual performance data. Thanks for the heads-up, very helpful.

See my question regarding exactly this issue on the previous page. So this is how it should work? At least it's a good start for further investigation. As stated before, I have always been wondering about what weird speeds the system sets during flap retraction. Now it could make sense, but I'll have to check the numbers against the actual performance data. Thanks for the heads-up, very helpful.

You're welcome. Confusing, isn't it? The FMC knows your instantaneous weight & calculates the exact speeds during the initial climb after takeoff & on the approach & sets these on the speed tape. It also sets the correct speeds (in green) on the speed tape during a go around but the magenta cursor drives to the speed for an aircraft at max weight! Doug

Confusing, isn't it? The FMC knows your instantaneous weight & calculates the exact speeds during the initial climb after takeoff & on the approach & sets these on the speed tape. It also sets the correct speeds (in green) on the speed tape during a go around but the magenta cursor drives to the speed for an aircraft at max weight!

Er sorry, now I'm confused (I think!). Your saying it calulates for max weight is how it should be... or how it actually is, on the NGX? Because what I see (speed bug wise), are values somewhat off to the flap maneuvering speeds (which are still displayed during the G/A IIRC). So I guess the bug is going for max weight here.However I never paid much attention to what the FD would command, I somehow thought it would command what the speed bug commands, but apparently that issue deserves a closer look again...

Er sorry, now I'm confused (I think!). Your saying it calulates for max weight is how it should be... or how it actually is, on the NGX? Because what I see (speed bug wise), are values somewhat off to the flap maneuvering speeds (which are still displayed during the G/A IIRC). So I guess the bug is going for max weight here.However I never paid much attention to what the FD would command, I somehow thought it would command what the speed bug commands, but apparently that issue deserves a closer look again...

That is how it works on the real aircraft & how it seems to work in the NGX although I have not studied it too closely in the NGX. The FD will command a pitch to satisfy the speed & ROC requirement at each stage of the go-around & the autothrust should provide the correct amount of thrust to achieve this. The problem with the NGX is the way it flies the initial go-round manoeuvre when it does not set sufficient go-around thrust to enable you to fly the correct pitch attitude at the correct airspeed with the correct ROC. Thankfully the real aircraft does it correctly! Doug

Ok, well I just grabbed some numbers from the performance data and tried to land at 60 tons and also at MLW, and the numbers seem to differ here and there, but some are always the same it seems. The first that appear when you start retracting to 15 is always something like 162, 164, 174. Apparently the flap 15 speed, although QRH suggests more than ten knots less. For 60 knots and appropriate V_REF I come up with 155, at MLW 161. So that's qutie a bit less. Retracing to 5 yields ten more, that's 184. Error remains. Retract to 1 gives 204 all the time, and flap up comes up with the last twenty knots and always goes up to 224 no matter what the weight. At some point during ONE of my attempts, the speed bug showed some obvious numbers at least: it would command flap maneuvering speed for the *next* flap setting (but correct numbers for *actual* weight). So retracting flaps to 5 would show flap 1 speed. Retract flaps to 1 would show flap up speed. Seriously no reason why it did that. Further investigation tomorrow...

Ok, well I just grabbed some numbers from the performance data and tried to land at 60 tons and also at MLW, and the numbers seem to differ here and there, but some are always the same it seems. The first that appear when you start retracting to 15 is always something like 162, 164, 174. Apparently the flap 15 speed, although QRH suggests more than ten knots less. For 60 knots and appropriate V_REF I come up with 155, at MLW 161. So that's qutie a bit less. Retracing to 5 yields ten more, that's 184. Error remains. Retract to 1 gives 204 all the time, and flap up comes up with the last twenty knots and always goes up to 224 no matter what the weight. At some point during ONE of my attempts, the speed bug showed some obvious numbers at least: it would command flap maneuvering speed for the *next* flap setting (but correct numbers for *actual* weight). So retracting flaps to 5 would show flap 1 speed. Retract flaps to 1 would show flap up speed. Seriously no reason why it did that. Further investigation tomorrow...

See Page 4.20.25 of the FCOMv2 for a technical description. Although the supplied manual is out of date the information shown here is still current. Doug

Ok, well I just grabbed some numbers from the performance data and tried to land at 60 tons and also at MLW, and the numbers seem to differ here and there, but some are always the same it seems. The first that appear when you start retracting to 15 is always something like 162, 164, 174. Apparently the flap 15 speed, although QRH suggests more than ten knots less. For 60 knots and appropriate V_REF I come up with 155, at MLW 161. So that's qutie a bit less. Retracing to 5 yields ten more, that's 184. Error remains. Retract to 1 gives 204 all the time, and flap up comes up with the last twenty knots and always goes up to 224 no matter what the weight. At some point during ONE of my attempts, the speed bug showed some obvious numbers at least: it would command flap maneuvering speed for the *next* flap setting (but correct numbers for *actual* weight). So retracting flaps to 5 would show flap 1 speed. Retract flaps to 1 would show flap up speed. Seriously no reason why it did that. Further investigation tomorrow...

What variant are you flying? I am flying the -800 which has an ultimate take-off weight of approx 79,000 Kg. Try loading up to this weight for take-off, then note the flap manoeuvring speeds as you extend the flaps on the approach. Yes, this is well above the normal max landing weight but this is permissable in an emergency since the 737 is unable to dump fuel. You will see the following bug speeds in green on the speed tape: Up = 224F1 = 204F5 = 184F15=174 These are the 'command' speeds demanded by the FMC during go-around regardless of your actual weight. In other words the speed that the magenta cursor will drive to even though the speeds for the actual weight will be shown in green on the speed tape. Cheers, Doug

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.

Sorry, but this is incorrect. During a go-around the MCP speed window is blanked & it is not possible to set any speed here. The speed is controlled by the FMC according to the existing flap setting. See FCOMv2 page 4.20.25 & my other posts above... Doug

Hello, thanks. Your FCOM reference really explained it - when you said max weight at first, I was looking for MLW numbers, not MTOW. I would not have assumed they were using MTOW numbers, but given your argument it might be the worst case scenario it actually makes sense. I will recheck the numbers, but I think we got it sorted out for me. And yes, I was always referring to the -800 model.

Hello, thanks. Your FCOM reference really explained it - when you said max weight at first, I was looking for MLW numbers, not MTOW. I would not have assumed they were using MTOW numbers, but given your argument it might be the worst case scenario it actually makes sense. I will recheck the numbers, but I think we got it sorted out for me. And yes, I was always referring to the -800 model.

It might seem a strange way of going about things but one advantage is that, at lower weights, you always have sufficient speed for flap retraction when you reach acceleration altitude without having to accelerate first. I just tried a go-around at a weight of 78 tonnes but the sim froze. Maybe it can't handle things at this weight?

LOL I will do more testing as well... Yeah, I figured they'd always have a safety margin that way. Then no wonder the speeds seem to be quite the same each time.

LOL I will do more testing as well... Yeah, I figured they'd always have a safety margin that way. Then no wonder the speeds seem to be quite the same each time.

Finally managed to get it to fly a go-around at 78 tonnes: The magenta cursor went exactly to the manoeuvring speeds I mentioned previously & this time they coincided with the green marks on the speed tape because the actual weight agreed with the FMC logic. However the initial response of the aircraft is still incorrect: whilst it applied more thrust as expected (due to the heavier weight) the pitch/power/ROC are still below what is to be expected. This is accompanied by a visual "PULL UP" warning on the PFD with an audio "TOO LOW GEAR" warning, both of which should not occur. Cheers, Doug

Finally managed

LOL My words of the day... finally "managed" to fly such go-around as well - been at least five attempt until I was finally there. First approach was a complete lockup when hitting TOGA. Interesting, second lockup, and both post HF4 install... bad sign? Second approach at least resulted in an actual go-around, but I forgot about my totally exaggerated force feedback joystick always throws the stick around like crazy when toggling the gear, resulting in AP disconnection and loss of TOGA pitch mode. [...] Finally it worked, and as you say, speeds were spot on (MTOW this time), also compared to manual again. Makes a lot more sense now. On my journey however the thing never stopped to amaze me. Without spoiling the fun, I will first let you have a close look at the following: And no, I'm neither talking about the rather liberal interpretation of "altitude HOLD", nor my abbreviated final approach (you can tell I was getting frustrated with all the futile go-around attempts...). Instead, my unshakable system understanding has always been that one can have one active mode per AFDS channel, plus an armed mode. Certainly less, but definately not more. Apparently though, the NGX has provisions for arming two pitch modes at a time - otherwise I see no explanation for G/S and V/S sitting perfectly next to each other, as opposed to centered as they would usually be. Or it's me, once again, and I'm missing another major point here. In fact I can even find it in the manual, but without further explanation. Enlighten me, whoever can come to rescue! Oh, got another one. Under certain circumstances (will have to investigate further, once again... sigh) it's impossible to cancel the wailer during the go-around. Probably during dual-channel operation, will check tomorrow. Anyways, you can hammer your Z button, it will only restart the wailer and the flashing red A/P light on the ASA won't exstinguish by any means. This behavior takes place until for example TOGA pitch modes gets replaced by ALT ACQ. Hitting Z then immediately silences the wailer, just as usual. I believe reclycling the FDs (and hence quitting TOGA mode) could also work. First I need to find a way to repdroduce though.

Edited October 6, 201114 yr by badderjet