Unstable on Approach After AP Disconnect

[adamant365 28]

Hi All,

 

I am wondering if PMDG has confirmed in any way that the FBW/handling behavior has issues or is being tweaked? For the third flight in a row, I had issues after disconnecting the AP to perform a manual landing from an ILS approach. I was fully established, had a very smooth 3deg glideslope, and was stable in trim. However, as I crossed the threshold at the "50" call out, the nose pitched up about 2 deg and my ROD decreased to about -450 fpm without and (and I mean ANY) input by me. It wasn't a wind gust (wind was steady 090@07 at RWY07R in VHHH), and I had also completely disabled AS2012's thermal effects.

 

It is very frustrating after a 10+ hour flight (compressed to about 4 hours) to have a nicely executed approach end with a fair bit of float and touchdown beyond the aiming point. I can't think of anything I would possibly be doing wrong and this is three flights in a row this has happened. In some capacity or another, I have had issues with manual landings since release (unless it is a manual circuit where the AP never controls the AC).

 

Is anyone else experiencing this and/or have PMDG confirmed there is an issue with FBW or manual control? Sometimes it just seems like the aircraft has a mind of its own when it comes to trim and this mysterious FBW system.

[hopskip 253]

Ground effect?

 

Regardless, you just described a pretty perfect flare

[Boeing or not going 578]

Floating on touchdown is the result of excess speed. But there have been complaints of the fbw system. i started a topic that ended up being a long discussion and a message from Ryan I believe saying they would look into it. I get annoyed fighting the airplane on approach so until a patch I fly mostly auto when with other airplanes I never do.

[adamant365 28]

Floating on touchdown is the result of excess speed. But there have been complaints of the fbw system. i started a topic that ended up being a long discussion and a message from Ryan I believe saying they would look into it. I get annoyed fighting the airplane on approach so until a patch I fly mostly auto when with other airplanes I never do.

Ok, thanks for this. You described it best with five words: fighting the aircraft on approach. That's exactly what I feel I'm doing.

 

I can tell you what I'm not doing is floating due to excess speed. I have the aircraft pretty much always nailed to VREF +5 from the FAF on down with AT on.

 

Either way, what is happening is it feels like the aircraft is pitching up on its own. I can see a subtle amount of ground effect being added, but i shouldn't have to use an aggressive forward pitch on the column to force my way through it. The aircraft should just settle and that is not what is happening. This is a definite pitch up at around 50 feet AGL. What's worse is sometimes trim seems to work and sometimes not.

[JC75 22]

Is it 50 ft you are kicking ap out?

 

I've had issues were I've noticed rudder trim, is no longer 0 and I've also found at times kicking autopilot out much earlier than your 50ft that I have to rapidly apply a lot of trim adjustment for same pitching up reasons. Seems depends on when aircraft is fetched out of ap, as to if I seem to inherit an out of trim aircraft or not.

[adamant365 28]

Is it 50 ft you are kicking ap out?

 

I've had issues were I've noticed rudder trim, is no longer 0 and I've also found at times kicking autopilot out much earlier than your 50ft that I have to rapidly apply a lot of trim adjustment for same pitching up reasons. Seems depends on when aircraft is fetched out of ap, as to if I seem to inherit an out of trim aircraft or not.

No, I generally disconnect the AP at the FAF/Glideslope intercept, whichever is later...so usually around 1000' AGL or so. What I'm seeing isn't that I'm inheriting an out of trim aircraft, rather that it is in perfect trim but trying to make further minor corrections is very difficult. And then there seems to be a slight pitch up movement around 50' AGL that is not commanded by me. With the late idle thrust reduction that the sim's A/T provides, I try to start my flare right at the "30" call but since I'm seeing this pitch up at around 50', it's very difficult to perform consistent landings.

[Driverab330 74]

Does it only happen when you land into VHHH? Have you tried any other airports?

 

The A/T go to idle at 25' RA. So yes if your sink rate is already at around 450fpm and you initiated the flare at 30' callout which means the airplane will actually pitch up at about 20-25' due to its inertia, you will float quite a bit.

 

This happens very often in real life when people experience a slight increase in head wind coming into land. In that case what people would do is pick another aiming point slightly further to your original one, hold the pitch till the 20'-30' call out then slightly raise the nose then hold it there just to soft the touch down a bit. You may need to manually reduce the thrust to idle slightly earlier as you raise the nose up instead of waiting for the auto thrust to act ( be a proactive pilot )

 

It's ok to touch down slightly firm initially, that will improve as you become more experience. To make you feel better, landing in Flight sim is much much Harder to judge than in real life due the lack of depth perception and peripheral vision. Anyways, landing at the correct position is much more important than making a soft landing to please the flight attendants. Because they can never see how much rwy you have got left in front of you.

 

Normal rate of descent at touch down is between 100-200' fpm.

 

Good luck on your next landing. : )

[dravid kenyala 6]

Is it 50 ft you are kicking ap out?

 

I've had issues were I've noticed rudder trim, is no longer 0 and I've also found at times kicking autopilot out much earlier than your 50ft that I have to rapidly apply a lot of trim adjustment for same pitching up reasons. Seems depends on when aircraft is fetched out of ap, as to if I seem to inherit an out of trim aircraft or not.

Hi. You said you trim a lot in this airplane. I have saitek yoke as well. at what point you do start trimming your aircraft? When you will be knowing the aircraft is out of trim? When to stop trimming. On what references like either watching the fd bar to be on centre line of artificial horizon by trimming it is not on the centre of artificial horizon.

When you will know this time I have to trim up and k this I have to trim nose down? Sorry man I am having trim buttons and I know that I have to trim but I don't know when to trim and what to see to initiate manual trimming. All the above questions are same but I want you to know my problem with trimming.

Thanks.

[adamant365 28]

Does it only happen when you land into VHHH? Have you tried any other airports?

 

The A/T go to idle at 25' RA. So yes if your sink rate is already at around 450fpm and you initiated the flare at 30' callout which means the airplane will actually pitch up at about 20-25' due to its inertia, you will float quite a bit.

 

This happens very often in real life when people experience a slight increase in head wind coming into land. In that case what people would do is pick another aiming point slightly further to your original one, hold the pitch till the 20'-30' call out then slightly raise the nose then hold it there just to soft the touch down a bit. You may need to manually reduce the thrust to idle slightly earlier as you raise the nose up instead of waiting for the auto thrust to act ( be a proactive pilot )

 

It's ok to touch down slightly firm initially, that will improve as you become more experience. To make you feel better, landing in Flight sim is much much Harder to judge than in real life due the lack of depth perception and peripheral vision. Anyways, landing at the correct position is much more important than making a soft landing to please the flight attendants. Because they can never see how much rwy you have got left in front of you.

 

Normal rate of descent at touch down is between 100-200' fpm.

 

Good luck on your next landing. : )

 It hasn't only happened at VHHH. My last four flights were PANC-VHHH, KATL-KLAX, KOAK-KMEM, and PANC-KCVG and I saw this behavior on landing at all four destinations since all four came off ILS approaches. I honestly don't think my technique is the issue here. I am able to correct by doing as you say...pick a new aim point and just land a little bit longer. What I'm more concerned with is the fact that there seems to be a slight uncommanded pitch up movement at 50' AGL that simply should not be there. If I'm not stable in pitch and/or have all pitch forces trimmed out by 100', I go around so I know I'm not out of trim. The only yoke movement I make below 100 is roll axis. And then it's only very slight to correctly line up.

 

I've been simming for quite some time, and have been using the CH yoke since at least '06 and I have never had an issue with an aircraft making any uncommanded pitch changes. Yes, I understand this is not the NGX, and the 777 has a complex FBW that the NG does not, but I can hardly believe the real 777 is this difficult to fly manually, especially on approach. The NGX is a dream to fly which as I understand it, it should be the other way around with the NG being tricky and the T7 being much simpler.

 

Now one thing I considered...isn't there some sort of movement of the "flippers" that occurs at about 50' AGL during landing as certain hydraulic systems come on line for landing?? Is it possible that somewhere in PMDG's code this pre-pressurization of these hydraulic systems is causing an issue for the sim?? I don't know....