Any news on HOLD mode bug at takeoff?

[Captain Kevin 586]

1 hour ago, EGLL said:

it seems to me you like your own sound in this forum.

WEL, no, not really, considering it's a little difficult to hear text on a forum. In any event, I'm not entirely too clear on what his point in bringing this issue up again was when it was established some time ago by Kyle that it was not an easy fix. Incidentally, I wasn't even the first one to respond to this.

[DEHowie 269]

Im telling you how it is in the real world. 

You need to get it that it is NOT a THRUST HOLD function on the Boeing like it is on an Airbus.

On a 320 and 330 which have a N1 or EPR hold function which is continually active and constant EPR you will see up to a 2% increase in N1 simply caused by ram effect on an EPR monitored aircraft. Now this is on a plane which IS maintaining a thrust setting.

The Boeing is NOT it is simply holding the thrust levers in whatever position they where in when the Throttle hold speed was passed. Hence there will be an increase in thrust due to RAM effect as the aircraft accelerates after it has passed the Throttle Hold speed. If your departing in strong headwinds you WILL need to set take off thrust by hand frequently after throttle hold has engaged as the aircraft will pass that airspeed at very low groundspeed.

Now whether P3D or Pmdg's logic is completely accurate is a different discussion with regard to the amount of spool up.

However the concept that the model is not accurate because thrust values increasing after throttle hold engages is NOT correct.

It is expected and does happen in the real world and a bug it isnt.

It is only prevalent between Throttle Hold and 400' AGL when Thrust Ref re-engages with Vnav.

Very observant mate but the Boeing autothrottle system has some weird "features" like Throttle hold, its numerous Vnav modes many which are counter intuitive and have traps awaiting every corner.

Converting from Airbus to Boeing for me is an eye rolling experience..lol..Airbus autothrust..its on or off easy. Boeing autothrust...its on then off but not really off then its back on..mostly..but if you move the thrust levers its on and off until you really need it then its definitely off and the toga button works most of the time except when you really need it.

Any wonder the NTSB ripped them apart...

 

 

 

[Dez 7]

19 minutes ago, Captain Kevin said:

WEL, no, not really, considering it's a little difficult to hear text on a forum. In any event, I'm not entirely too clear on what his point in bringing this issue up again was when it was established some time ago by Kyle that it was not an easy fix. Incidentally, I wasn't even the first one to respond to this.

 Yes Kevin, but he is a PMDG customer and he is entitled to ask as many times he wants to.
If he doesn't get a message, from the forum member is no point keep repeating he is not going to listen to any one.

All the best

Mo Dez

[jgoggi 65]

8 minutes ago, DEHowie said:

However the concept that the model is not accurate because thrust values increasing after throttle hold engages is NOT correct.

It is expected and does happen in the real world and a bug it isnt.

 

Darren, I appreciate your effort to get a logic explanation, but please, let's not discuss whether it's a bug or not, it has widely been aknowledged that it IS a bug, no doubt. No real life 747-400 (and not even the Aerowinx PSX, that is another very faithful copy of a real life 747-400) has that behaviour of constantly increasing N1 between 80 knots and 400 ft...

[icemarkom 59]

James, as a peanut-gallery observer, I gather Darren is an actual 747 pilot, and bases his answers on his experience with an actual aircraft. May I politely inquire whether you are arguing from the same position, i.e. you fly 747, and notice discrepancies; or are you just detail-oriented flightsim enthusiast as many of us are? Darren, also, please correct me if I am wrong in my assumption. 

[Captain Kevin 586]

7 hours ago, EGLL said:

 Yes Kevin, but he is a PMDG customer and he is entitled to ask as many times he wants to.
If he doesn't get a message, from the forum member is no point keep repeating he is not going to listen to any one.

Asking is one thing, but being a paying customer doesn't give anybody the right to be disrespectful, either. The last few posts he made regarding the matter made it seem like it was either an easy fix or PMDG was somehow being the bad guy by intentionally withholding the fix, in which neither is the case. At one point, he even expected that this issue should be treated with the highest priority and everybody should just drop whatever else they're doing. That I have a problem with, especially seeing that there were people out there that had issues where they actually weren't able to fly the plane. As far as I'm concerned, those issues are the ones that need to be dealt with first.

[DavidP 1,408]

9 hours ago, jgoggi said:

No real life 747-400

Unless you have experience, how can you say that? I will take the word from someone like Darren who is clearly qualified on this equipment and is experienced, over enthusiasts who spend hours analysing Youtube videos. Why not just give it a rest until PMDG give a firm position on the matter. Quite frankly, you're starting to make yourself look silly.

[icemarkom 59]

1 hour ago, Captain Kevin said:

Asking is one thing, but being a paying customer doesn't give anybody the right to be disrespectful, either. The last few posts he made regarding the matter made it seem like it was either an easy fix or PMDG was somehow being the bad guy by intentionally withholding the fix, in which neither is the case. At one point, he even expected that this issue should be treated with the highest priority and everybody should just drop whatever else they're doing. That I have a problem with, especially seeing that there were people out there that had issues where they actually weren't able to fly the plane. As far as I'm concerned, those issues are the ones that need to be dealt with first.

I for one find the autobrake issue with 777 a much more noticable, yet I am fine waiting for the fix.

 

It's software. It will be riddled with bugs. And that's OK. Whoever claims software has no bugs, clearly has no idea what they're talking about :-). That, too, is OK.

[Captain Kevin 586]

9 minutes ago, icemarkom said:

I for one find the autobrake issue with 777 a much more noticable, yet I am fine waiting for the fix.

Exactly.

[Nighthwk 566]

How about PMDG gives James the source code for the autothrottle system and lets him solve the problem if it's such a quick and easy fix.

[PinkPony 171]

 

13 hours ago, DEHowie said:

The thrust increasing is a natural effect seen on every jet aircraft i have flown.

The throttle hold mode(note its NOT thrust hold) is a mode whereby the autothrottle sets the limit thrust(Thrust ref)...on reaching HOLD(65-80 kts airframe dependent) speed the autothrust no longer can modify engine thrust. Ie it sets the thrust then depowers the servos to the thrust levers to ensure an autothrottle issue cannot reduce thrust.

It isnt an active system ie continually keeping the thrust the same like the Airbus system which continually maintains the desired EPR or N1.

As the aircraft with thrust set accelerates and the autothrottle in hold and no ability to adjust thrust accelerates ram effect will increase engine rpm ie N1 and can change EPR.

Here is an extract from our 787 manual...the 747/777/767/757 are all identical in application of Throttle Hold mode.

Quote...

The PM should verify that takeoff thrust has been set and the throttle hold mode (HOLD) is engaged. Once HOLD annunciates, the autothrottle cannot change thrust lever position, but thrust levers can be positioned manually. The HOLD mode remains engaged until VNAV engagement or another thrust mode is selected. 
Note: Takeoff into headwind of 20 knots or greater may result in HOLD before the autothrottle can make final thrust adjustments. 

The HOLD mode protects against thrust lever movement if a system fault occurs. Lack of the HOLD annunciation means the protective feature may not be active. If HOLD annunciation does not appear, no crew action is required unless a subsequent system fault causes unwanted thrust lever movement. As with any autothrottle malfunction, the autothrottle should then be disconnected and desired thrust set manually.

 

The engines spinning up due to Ram effect occurs on EVERY engine on every jet out there. As you can see its not a THRUST HOLD function but THROTTLE HOLD designed to not hold a set thrust setting but depower the autothrottle servos and stop a malfunction reducing thrust catastrophically.

 

 

Darren, you are of course correct. However, James is too in saying that there is a verified bug. What he didn't mention this time around, is that this bug is specific to the GE powered -400s only.

The PW and RR powered aircraft (EPR vs. N1 on the GE), are setting thrust with TOGA and maintaining it throughout HOLD, with the minor realistic variation you describe as the RAM effect increases.

On the GE -400s (still present as of the latest version), the N1 continues up to 4-5% above target until THR REF at 400' AGL kicks in. 

 

18 hours ago, jgoggi said:

Hi, just out of curiosity, how is the fixing of the increasing thrust during HOLD mode at takeoff going? Did you manage to find out what it is caused by? I suppose you have been working on it for more than 4 months, now, it must really be a tough issue.

Thanks.

 

 

James, 

I have reported dozes of "bugs" over the years for the B777 and B744, and continue to do so as I discover them. > 95 % of them have been addressed. The eagerness of a development team that is always looking to improve their products, is precisely the reason why PMDG products are this good. 

I also wish that every single ticket/item/bug could be resolved within days being reported, after PMDG investigate/acknowledge it. However, this is simply not possible.

RSR has discussed how the recent P3D v4 transition has taken up a lot of the teams time. Furthermore, he has also mentioned the 600 or so items for the B777 alone, that may or may not make their way to us, through updates. The issue here is development time, and being able to devote the necessary resources.

You have to remember that PMDG is a business. They have A development schedule and timelines. Unlikely that they throw all this out of the window, to address a "bug" which ultimately does not prevent us from flying the aircraft. That is why you see specific bugs being addressed in the change-log over others. Such as the annoying clicking noise from the B777 A/B selector (a result of the v3 to v4 transition).

At this point, following release the -400 has only had one major change-log, which was  followed by a second smaller one. The remainder have all been to to get v4 going, for which I am very grateful considering the short time it took them. In addition to other stability/performance changes with installers etc.

I am 100% certain they will address countless outstanding items, including the one we are discussing in a upcoming update for the QOTS II. Hopefully sooner rather than later. At the latest with the -8 release. This is safe to assume, considering they will want to bring the code up to speed with the -8. 

I am certain that continuously posting in this forum is not going to get it fixed any sooner. If you opened a ticket for the original bug report, it can never hurt to follow up with a nice message to the support staff. 

P.S. Dont forget, the team are currently working on the -600/700 v4 transition and DC-6 P3D release.  

 

[MauB 74]

Watch the video below (from a 400ERF) and you can see the N1 going above the limit for a short time. There are some other videos which I couldn't find showing the same engine behavior during takeoff roll and even during climb. So it looks like it's not a bug.

 

[PinkPony 171]

2 hours ago, MauB said:

Watch the video below (from a 400ERF) and you can see the N1 going above the limit for a short time. There are some other videos which I couldn't find showing the same engine behavior during takeoff roll and even during climb. So it looks like it's not a bug.

 

 

Your video has nothing to do with what James reported in his ticket.

What you see here is the commanded thrust, very briefly jumping above the target N1,rjustt as TO/GA is selected. This corrects itself almost instantaneously, and before HOLD kicks in. Once power is set, and HOLD comes on, the N1 remains within 1% of target N1. With the GE's in the QOTS II, the N1 continues to rise and rise until 400ft. 

 

To make it very simple. 

The -400 with PW and RR engines are behaving behaving absolutely correctly. Do a takeoff in the SIM, and observe your EICAS indications. Keep a close eye on actual EPR vs. target EPR from brake release up to 400ft.

Result? Within .03 EPR from brake release up to THR REF at 400ft AGL. Just as it is designed to function.

 

Now..a GE -400.... and observe your EICAS indications. Keep a close eye on actual N1 vs target N1 from brake release up to THR REF at 400ft AGL. You will see a distinctively different behavior to the PW/GE. Commanded N1 will continue to rise and rise above target N. (4-5%). Deal beaker? No of course not. Certainly a bug, and one that has already been reported, acknowledged and will be addressed..

 

P.S. The identical bug was present on the B777 upon release. 

Can we put this to rest now, and wait for the fix?

 

 

 

[MauB 74]

You are right regarding the bug, I stand corrected.
I could be wrong but I remember seeing this issue with any engine variant. Not a deal breaker for sure.

[craig_read 43]

James,

I noticed it still requires a fix, but if there has been no announcement or response to your ticket, it's safe to assume no news.  I am sure they'll be in touch when something changes.

To those who are arguing that this is not a bug.. the facts are, it is a bug, and this bug has been accepted by the team.  It is true that the videos shown here show slight drift in the thrust during takeoff, but not the steady increase of thrust during take off seen in the PMDG rendition.  This doesn't make the product unusable, but I can understand the frustration it causes.  I guess the fact things like this are being reported as bugs is a testament to the level of quality and faithful replication the sim community has come to expect from them, and the keen eye of simmers... you could say PMDG are a victim of their own success ;)