Manually Closing Thrust Levers And HOLD mode

[Mike777 163]

As I recall, the Asiana PF put the aircraft into FLCH to descend faster.  He didn't realize that the MCP altitude window was set to the go-around altitude, which was higher than the aircraft was.  So the aircraft started to climb and increase thrust.  He then pushed and held the throttle handles at minimum and disconnected the autopilot.  At that point the throttles went into HOLD and stayed there.  I believe I tried it and this particular (non-standard) situation is not simulated by PMDG.   If he had used VNAV, the problem would not have arisen.  If the plane is more than 300 ft below the (presumably go-around) set altitude in VNAV, the aircraft will continue to follow the descent profile.

 

I also learned the hard way about another situation in which the A/T will go into HOLD on final.  If VNAV is the vertical mode (even w/ autopilot turned off) and the aircraft is flying above the VNAV profile, the A/T will go into HOLD to bring the aircraft back down to the profile.  If the plane stays above the profile the A/T will stay in HOLD.  I filed a ticket about this w/ PMDG and they believe this is proper performance.  How did I learn about this?  The KJFK VOR 13 Left approach.  I had VNAV set, but I also tuned the 13L ILS.  Autopilot off (the final approach can't be flown by the A/P).  But I used the 13L GS indicator for my descent, rather than the VNAV profile.  The VNAV profile is lower than the GS slope.  So the A/T went into HOLD and stayed there.  The results were not pretty.  A good reason to choose either an RNAV approach or an ILS one, but not both!  As was discussed in another thread, there is a good reason the FMC doesn't autotune the LOC/GS frequency on an RNAV approach.

 

Mike

[Alpha Floor 237]

To anyone interested, I found the Boeing report submitted to the NTSB here

 

This other pilot here mentions that:

 

 

What transpired was that they had left their "flight director" system which included the autopilot, partially on. As such, this would prevent a "wake-up" from taking place. Effectively, the lack of ‘wake-up’ meant that the auto throttle was not going to prevent the plane's speed from slowing down. In other words, the pilot needed to manually move the levers. This is Boeing's philosophy to allow pilots to override full automation

Of course, this design by Boeing has its flaw. This ‘wake up’ feature had been raised before during the certification of the Boeing 787 Dreamliner.

According to the NTSB which quoted a FAA report - this was a “less-than-desirable feature and it could be improved upon."

Hence, if the autopilot is disconnected and the auto-throttles are left “armed,” the thrust would hold in idle power and would not automatically increase to the target airspeed.

 

This pilot mentions, as I did before, the fact that the crew didn't reset BOTH F/Ds. Had they done so, they would have cleared the FMA and the AT would have waken up.

 

But in any case I think it's fair to say that this logic of the AP/AT system on the real 777 is not making everybody happy...

[Mike777 163]

Honestly, I have never understood why the 777 A/T would allow the airspeed to approach or go below the stall speed during final approach, in ANY conceivable situation.  

 

Mike

[Alpha Floor 237]

Honestly, I have never understood why the 777 A/T would allow the airspeed to approach or go below the stall speed during final approach, in ANY conceivable situation.  

 

Mike

 

I agree. In my opinion this is a serious inconsistency of the "wake-up" function. Either it works *always* or it better never works. 

 

However, the crew of the Asiana flight were not, I believe, hoping that the ATs woke up. No pilot should relay on a last resort feature, ever. I think they thought the ATs would revert to SPD and track the 137kt on the speed window. Obviously they weren't paying attention either to the FMA nor to the ASI. The most amazing thing is, there were 3 pilots in the cockpit, and one of them was an Instructor (!!!)

[Tony747-400 44]

Can we say as I haven't had a chance to test yet, for the PMDG 777 to act as the real aircraft with manually closing the Thrust Levers and going into HOLD mode, you have to change the settings of your hardware via the FMC to A/T Overide to "ALWAYS"?

[Alpha Floor 237]

Can we say as I haven't had a chance to test yet, for the PMDG 777 to act as the real aircraft with manually closing the Thrust Levers and going into HOLD mode, you have to change the settings of your hardware via the FMC to A/T Overide to "ALWAYS"?

 

Hi Tony. Common sense indicates that yes, AT override should be at ALWAYS because otherwise moving your hardware throttles won't have any effect.

 

If you do it via the keyboard, when you press F1, can you tell if the levers in the cockpit physically move all the way back to idle?

 

I tried it with manual override via my hardware and it DID NOT work.

[Alpha Floor 237]

Any updates on this guys?

[scandinavian13 5,192]

Any updates on this guys?

 

...in terms of?

[Alpha Floor 237]

...in terms of?

 

Well, the initial question of the OP hasn't been answered yet.

 

The issue is trying to find out if the PMDG 777 will behave like in the Asiana accident, i.e, when in THR | FLCH, if the thrust levers are manually closed, the thrust mode reverts to HOLD. When they are advanced again, it reverts back to THR.

[scandinavian13 5,192]

Well, the initial question of the OP hasn't been answered yet.

 

The issue is trying to find out if the PMDG 777 will behave like in the Asiana accident, i.e, when in THR | FLCH, if the thrust levers are manually closed, the thrust mode reverts to HOLD. When they are advanced again, it reverts back to THR.

 

Kinda makes you wonder if there's some, specific place people can go to report issues...

[Alpha Floor 237]

Kinda makes you wonder if there's some, specific place people can go to report issues...

 

Yes Kyle, I believe we all know about the ticket system. I used it recently.

 

The thing is I don't want to submit a ticket if I'm not sure whether the problem is on MY side or on PMDGs side. That's what the forum is for, I guess...

[scandinavian13 5,192]

 

 

Yes Kyle, I believe we all know about the ticket system. I used it recently.

 

Saw that.

 

 

 

The thing is I don't want to submit a ticket if I'm not sure whether the problem is on MY side or on PMDGs side. That's what the forum is for, I guess...

 

I appreciate that, but if you believe you've found something worth looking at, it's best to go to the queue, particularly if you're looking for us to have a look at it.

[Alpha Floor 237]

Dear all,

 

I did submit a ticket about this issue, I will keep you guys informed on the reply by the support team!

 

Also I want to quote from the Boeing Asiana 214 accident report page 37 regarding the AT HOLD mode:

 

 

 

When using Flight Level Change (FLCH SPD), the autothrottle, if armed, will enter the thrust
mode (THR) and adjust thrust to a level that will achieve the commanded change in altitude over
about a two minute period, if possible. The pilot can alter this two minute period by manually
changing thrust, without having to disconnect the autothrottle. For example, if a FLCH SPD
climb is commanded the airplane will begin to climb. The pilot can increase thrust to achieve the
climb faster (in less than 2 minutes), or decrease thrust to achieve the climb more slowly (in
more than 2 minutes). When this manual override occurs, the Autothrottle goes into HOLD
mode, which acknowledges that the throttles are being controlled by the pilot. This mode change
is annunciated on the FMAs and surrounded by a green box for 10 seconds to emphasize it.

[Alpha Floor 237]

So apparently this is a known issue. Because of hardware/flight simulator integration issues, and because most of us don't have servo-backdriven thrust levers, it would have been problematic to realistically represent this feature of the AT system of the real 777.