Auto throttle speed control

[Vollie 11]

[MarkW 1,490]

The engines are definitely slower to react than the NGX but I have to wonder where you had the speed bug.  In windy conditions you need to fly at a higher speed to compensate for fluctuations in the aircraft speed caused by the wind.  If you have the speed bug at the lower limit then yes you could have a problem.

[Vollie 11]

The engines are definitely slower to react than the NGX but I have to wonder where you had the speed bug.  In windy conditions you need to fly at a higher speed to compensate for fluctuations in the aircraft speed caused by the wind.  If you have the speed bug at the lower limit then yes you could have a problem.

I know what you mean, but that is not the problem. I added 5 knots more to save iT. But te autothrottle is not holding the select speed. The speed goes slower and slower iTS reducing power and becomes in te stall area. I think no one of the pilots like that to operate at that speed.

[Vollie 11]

The engines are definitely slower to react than the NGX but I have to wonder where you had the speed bug. In windy conditions you need to fly at a higher speed to compensate for fluctuations in the aircraft speed caused by the wind. If you have the speed bug at the lower limit then yes you could have a problem.

Oh Im sorry I forgot to say that VREF speed

Was 145 and I added 5 knots to it. So I types 150 knots for the landing. But the problem is the autothrottle was slowing down and not holding the given speed in de fmc.

[sosuflyer 30]

Oh Im sorry I forgot to say that VREF speed

Was 145 and I added 5 knots to it. So I types 150 knots for the landing. But the problem is the autothrottle was slowing down and not holding the given speed in de fmc.

The autothrottle does not pay attention to the approach speed set on the approach page in the fmc. You have to actually set the speed you want in the MCP speed window

[Vollie 11]

The autothrottle does not pay attention to the approach speed set on the approach page in the fmc. You have to actually set the speed you want in the MCP speed window

Thats what I did, I had put iT into mcp. I dont know why the speed was descresing

[MarkW 1,490]

Are you sure one of the speed modes was active?  You can check by looking at the Green at the top of the HSI display.  Should say THR HOLD, or some other indication to show that the A/T is actually engaged.  Just trying to think of things that could be a problem.   I have never had this issue on the 777.

[sosuflyer 30]

Thats what I did, I had put iT into mcp. I dont know why the speed was descresing

Ok, that's one thing crossed off or list.

 

In addition to what MarkW said, we need to know more:

 

1 version number of your 777 installation

2 what kind of approach are you making (rnav, rnp, ils, visual, etc)

3 are you using autopilot to fly the approach

4 autopilot modes used during approach (the green boxes above the hsi on the pfd, as well as the physical buttons pressed on the MCP)

5 hardware throttle usage and settings ( like nullzones and throttle override settings in the PMDG menu in the fmc)

 

Try and get that info for us and we can help you out and see if it's user error or not

[Vollie 11]

Ok, that's one thing crossed off or list.

In addition to what MarkW said, we need to know more:

1 version number of your 777 installation

2 what kind of approach are you making (rnav, rnp, ils, visual, etc)

3 are you using autopilot to fly the approach

4 autopilot modes used during approach (the green boxes above the hsi on the pfd, as well as the physical buttons pressed on the MCP)

5 hardware throttle usage and settings ( like nullzones and throttle override settings in the PMDG menu in the fmc)

Try and get that info for us and we can help you out and see if it's user error or not

1 version no 1.10.6061

2 making ILS approach

3 yes using autopilot, but disengaged Because 2 times chance to stall.

4 autopilot Modes used during approach all green lights were on the HSI.

5 autothrottle override NEVER im using throttles.

 

I want to say that there was a lot of headwind and turbulence.

I dont know if this is a reason that the throttle cant holding the speed. Sometimes at descend the same problem meanwhile throttle engaged and mcp spd on.

 

 

[Mike777 163]

autopilot Modes used during approach all green lights were on the HSI.

 

Hi, Volkan,

 

Did the green light on the left say "SPD" or something else?  The light on the left tells you what mode the autothrottle is in.  What did the green light on the right say (vertical mode)?

 

Mike

[Vollie 11]

Hi, Volkan,

 

Did the green light on the left say "SPD" or something else?  The light on the left tells you what mode the autothrottle is in.  What did the green light on the right say (vertical mode)?

 

Mike

Hi Mike,

 

Thanks for your message. I cant remember what was on the display slowing in green light. But I know that I clicked on the spd button and selected the VREF speed. I selected speed 145+5 150 kts

[Mike777 163]

 

 

Thanks for your message. I cant remember what was on the display slowing in green light. But I know that I clicked on the spd button and selected the VREF speed. I selected speed 145+5 150 kts

 

Hi, Volkan,

 

It is possible that the autothrottle went into HOLD mode, although it should not do that if you activated approach on the MCP.  However it might be possible if you used a VNAV or FLCH descent and then switched off the autopilot and followed the loc & glideslope manually -- I'm really not sure.  The Asiana crash last summer was in large part caused by the pilots not realizing they had forced the autothrottle into HOLD mode and then not watching the actual speed.

 

If you can reproduce the situation where the autothrottle fails to maintain the proper speed, see what is showing in the left green indicator (assuming it is lit).  This shows the autothrottle mode.  Also make sure the autothrottle is on, not just armed, and the proper speed is showing in the MCP speed window.  Finally, make sure that VREF is showing on the pfd (which I believe requires you to select it in the CDU approach window by clicking on the setting you want -- for example flaps 30/145 and then entering it right below on the right -- or manually entering it). 

 

Really curious to know what went wrong!  The autothrottle is supposed to be able to handle gusts and you dialed in extra speed.  If the speed drops below VRef it is supposed to crank up automatically, even if this results in a speed higher than the target one.  If the speed is too high, it is supposed to reduce thrust, but not as rapidly.  But you lose all of this if the autothrottle goes into HOLD. 

 

Mike

[Nixon 30]

Hello pilots,

 

I had update my b777 300ER. During landing To VHHH airport I experienced Some problems with the autothrottle speed controlling. There was Some wind from 230 at 10kts and outliers with 20 Kts something like that. The autothrottle does not follow the input speed limits exactly, this results for me two times in a stall. So I had disabled the autothrottle and used the throttle manually. Did I Anything wrong? Or is that a known problem with the 777? Because I never experienced this error with the 737 ngx.

 

Please tell me your experience about this error

The only time I have had this happen in the  PMDG 777 is landing at Manchester UK the other night. The weather was very poor ( I suspect in real life they may have not attempted to land until things calmed down a bit). The A/T was in hold mode (I have the A/T in the PMDG override when in hold mode). I moved the throttle forward and the speed still decreased for a little while and then as the engines spooled up the speed increased slowly. I disconnected the A/T and set the thrust to give me a Vref speed plus around 12 knots. I put it down to the large engines taking a while to spool up and also as I think the IAS was partly increasing and decreasing due to the weather and at a greater rate than the A/T could spool the engines up or down. That's why I disconnected the A/T and flew with the higher Vref speed.I didn't attempt to keep exactly to the vref plus 12 speed but adjusted the throttles once it was obvious that the speed was increasing or decreasing by about 4 knots.

 

I have no idea if what I did is the accepted way to deal with this but it leads me to think that you may have had a similar thing happen to you and therefore it's unlikely that it's hardware related.

 

Finally I used to live in Hong Kong and I know that Chek Lap Kok airport can have very bad down draughts from the hills on Lantau island immediately to the south of the airport. So I think that you would have at least as bad conditions as my Manchester landings. I'm old enough to have experienced landing many times at the old Kai Tak airport and even just as SLF it was always fun especially when on finals as you could look out and see the TV's on in the adjacent flats.

[777simmer 117]

You should never see HOLD mode during final approach!

 

That is how Asiana crashed (as was mentioned already)!

 

When on an ILS with LOC and GS captured (both green) the AT will be in SPD mode (green) which is good.

Only in SPD mode will the AT keep your speed.

[jbassue 181]

This happened to me the other day. The A/T did not respond to the decrease in IAS and did not bother to try holding the speed set in the speed window, which was VREF + 5 knots.

It remained at idle while approaching the amber line, I think it was because of changing wind during the final. 

 

EDIT: the A/T never commanded idle thrust, but it seemed to maintain about 50% N1 regardless of a decreasing IAS

 

 

So, I responded by deactivating A/T which isn't recommended during normal landing procedure, and manually controlled throttle input for the last portion of landing;