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Tony747-400

Manually Closing Thrust Levers And HOLD mode

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Hi Guys.

 

I'm of the understanding that when you manually close the Thrust Levers to idle thrust the aircraft will go into HOLD mode and will be shown on the FMA. This understanding comes from watching a YouTube video in the Asiana incident at KSFO.

On my sim (P3D V3) when I close the Thrust levers using the F1 key the aircraft stays in SPD mode and the Thrust Levers will move again automatically to regain the intended thrust. What is the correct behaviour of the aircraft when manually closing the Thrust Levers, should it go into HOLD mode? If so how do I get HOLD mode to become active?

 

Thanks for any help

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I'm of the understanding that when you manually close the Thrust Levers to idle thrust the aircraft will go into HOLD mode and will be shown on the FMA.

 

This understanding is incorrect. When in HOLD mode, you are in control of the throttle position, despite AT being technically ON.

 

 

 


On my sim (P3D V3) when I close the Thrust levers using the F1 key the aircraft stays in SPD mode and the Thrust Levers will move again automatically to regain the intended thrust.

 

This is correct.

 

 

 


What is the correct behaviour of the aircraft when manually closing the Thrust Levers, should it go into HOLD mode?

 

No.

 

 

 


If so how do I get HOLD mode to become active?

 

Enter a throttle regime where HOLD is commanded. The main ones are:

  • After 80ish knots in TOGA
  • After a commanded IDLE in VNAV

 

 

 

Always go to the manuals. YouTube content is very often incorrect. At the very least, in many cases, it is not clearly explained as evidenced by the discussion here.

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As Kyle said, what you experience is the expected behavior of the plane.

 

If the AT is any mode other than HOLD, the pilot can "override" by moving the thrust levers by hand. As soon as he releases his hand, the levers will move back to their previous position (+ a possible correction).

 

In HOLD mode, the servos are disconnected from the thrust levers. The pilot can move the levers, release his hand and they will stay where they are left.

 

I don't know how it is on the 737, bu on the 777, if the the levers are on an IDLE HOLD (or disengaged) and the aircraft slows down below Minimum Maneuvering Speed, the AT will "wake up" anyway and speed up to MMS. You can see this wake-up function in action here.

 

 

 

 


Enter a throttle regime where HOLD is commanded. The main ones are:
After 80ish knots in TOGA
After a commanded IDLE in VNAV

 

I might add:

 

After a commanded IDLE in LVL CH (level change)


EDIT: Regarding the Asiana accident, which was a 777 not a 737, I don't understand how the aircraft could slow down below MMS with ATs ARMED. Whenever they are armed, they will wake up and spool up the engines to accelerate at least back up to MMS. In the Asiana accident, what I read was that the airspeed got indeed below MMS with an "AIRSPEED LOW" warning on the EICAS, aural warning and all.

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I know YouTube videos you have to be careful of for factual accuracy but I thought this video was from the official report from the NTSB report to the KSFO incident. The video shows the aircraft in V/S mode descending, FLCH is selected which started a climb to the MA altitude. The pilot disconnected the autopilot and it states that the pilot closed the Thrust Levers which put the aircraft into HOLD Mode. Maybe if you have the time to see the video you could comment and see why I am asking this question.

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I don't understand how the aircraft could slow down below MMS with ATs ARMED.

 

Because the A/T will not wake up in FLCH.

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Tony, for convenience of other users you could link us to the video you saw please! That way we don't have to look for it and guess :)

 

 

 


the pilot closed the Thrust Levers which put the aircraft into HOLD Mode

 

There's a misunderstanding in that sentence somewhere. Either the video didn't explain it properly (which is possible) or you didn't understand it correctly. Anyway, that's not what the aircraft does as Kyle said. Maybe the pilot closed the levers BUT AT THE SAME TIME as FLCH was doing it because it went into hold. The relation is not: pilot closes levers -> plane goes into HOLD.


Because the A/T will not wake up in FLCH.

 

Oh really? Didn't know that! Will try it out. In any case if that's true, I'd say it's a design flaw on Boeing's behalf...

 

Maybe the pilots had the exact same misunderstanding on the system that I just displayed right here.

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Tony, for convenience of other users you could link us to the video you saw please! That way we don't have to look for it and guess :)

 

 

 

 

There's a misunderstanding in that sentence somewhere. Either the video didn't explain it properly (which is possible) or you didn't understand it correctly. Anyway, that's not what the aircraft does as Kyle said. Maybe the pilot closed the levers BUT AT THE SAME TIME as FLCH was doing it because it went into hold. The relation is not: pilot closes levers -> plane goes into HOLD.

 

 

Oh really? Didn't know that! Will try it out. In any case if that's true, I'd say it's a design flaw on Boeing's behalf...

 

Maybe the pilots had the exact same misunderstanding on the system that I just displayed right here.

https://youtu.be/QVaQYhd_Qy0

 

Here's the link

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Oh really? Didn't know that! Will try it out. In any case if that's true, I'd say it's a design flaw on Boeing's behalf...

 

I wouldn't go quite that far. You could make a similar argument that the aircraft should then also be double checking pilots in all kinds of other situations. As an example, if the descent rate is "too high" after the RA starts picking up returns, it would be a "design flaw" that the aircraft not "wake up" and take over your command instructions to not allow such a thing. You could also put yourself right into the side of a mountain in ALT HOLD. Is it a design flaw to not force a climb any time you get a GPWS alert? You're the PF. Your job is the safe operation of the aircraft. It is not the responsibility of the automation - ever.

 

FLCH, as a speed mode, is a THR + PITCH mode. You use pitch to hold the speed based on IDLE (or pilot-set) or FULL thrust. Its sole job is to allow you to maintain a speed through pitch on idle or the limit. If you decide to take over the pitch regulation, then it is your job to ensure you're on speed. You can underclimb (trend toward overspeed), over climb (trend toward stall), under descend (trend toward stall), and over descend (trend toward overspeed) the set airspeed if you set this mode and not regulate pitch effectively.

 

The pilots should've changed back into SPD HOLD - that's what they were assuming the AT was doing, ignoring the FMA the whole time apparently.

 

 

 

 

Here's the link

 

When you were testing your own situation, were you also climbing or descending without the AP, while in FL CH mode?

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Why would you even press the FLCH button on final approach? That seems like a very bad idea to me.

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Why would you even press the FLCH button on final approach? That seems like a very bad idea to me.

 

They were high on profile, so selected FLCH in order to get a higher rate of descent. In principle fine, but the problem is that when hand-flying in FLCH if you ignore the FD commands you will end up in bother, because as mentioned, the A/T will not re-engage until the mode changes to a speed-on-thrust mode (i.e. ALT, G/S, V/S etc etc).

 

Boeing says it considered changing the mode to automatically wake up. Bob Myers, flight deck chief engineer, says—for this particular design—they were faced with a choice. “If we did a wake-up or some sort of mode transition of the autothrottle and hold mode for a low-speed condition, we would have had a mode transition without the pilots authorizing that change.” He says the change would have resulted in two systems trying to control speed—the autopilot and the autothrottle. “We looked at the two situations and felt that the less confusing was the design we chose.”

http://aviationweek.com/awin/777-autothrottle-design-highlighted-asiana-crash 

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I wouldn't go quite that far. You could make a similar argument that the aircraft should then also be double checking pilots in all kinds of other situations. As an example, if the descent rate is "too high" after the RA starts picking up returns, it would be a "design flaw" that the aircraft not "wake up" and take over your command instructions to not allow such a thing. You could also put yourself right into the side of a mountain in ALT HOLD. Is it a design flaw to not force a climb any time you get a GPWS alert? You're the PF. Your job is the safe operation of the aircraft. It is not the responsibility of the automation - ever.

 

FLCH, as a speed mode, is a THR + PITCH mode. You use pitch to hold the speed based on IDLE (or pilot-set) or FULL thrust. Its sole job is to allow you to maintain a speed through pitch on idle or the limit. If you decide to take over the pitch regulation, then it is your job to ensure you're on speed. You can underclimb (trend toward overspeed), over climb (trend toward stall), under descend (trend toward stall), and over descend (trend toward overspeed) the set airspeed if you set this mode and not regulate pitch effectively.

 

The pilots should've changed back into SPD HOLD - that's what they were assuming the AT was doing, ignoring the FMA the whole time apparently.

 

 

 

 

When you were testing your own situation, were you also climbing or descending without the AP, while in FL CH mode?

I was doing the same as the video, selecting FLCH initiated a climb, I disconnected the Autopilot and pushed the nose down and started a descent. I pressed F1 to close the throttles expecting HOLD mode, but I stayed in SPD and the throttles would power up automatically to regain required thrust.

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I wouldn't go quite that far.

 

I see your point Kyle, which is very valid. I believe though that the protection system of the aircraft should be consistent. To me it doesn't make much sense that the ATs will wake up if they are DISENGAGED, but not if they are ENGAGED at IDLE HOLD in FLCH. The feature is not being consistent. Either it does NEVER let the aircraft slow down below MMS as long as the ATs are armed, or it shouldn't be installed at all.

 

As I'm reading it also seem like the NTSB agrees with me. For some reason I can't seem to reach the NTSB website now to get the actual report, but as you can read in this article that quotes from the report:

 

 

The NTSB found that there were also several contributing causes:

 

  • Complex autothrottle and autopilot flight director systems that were inadequately described in Boeing’s documentation and Asiana’s pilot training,

They were high on profile, so selected FLCH in order to get a higher rate of descent. In principle fine, but the problem is that when hand-flying in FLCH if you ignore the FD commands you will end up in bother, because as mentioned, the A/T will not re-engage until the mode changes to a speed-on-thrust mode (i.e. ALT, G/S, V/S etc etc).

 

http://aviationweek.com/awin/777-autothrottle-design-highlighted-asiana-crash 

 

That's very interesting Tony, thanks for quoting because I can't seem to access that website. As I remember Aviation Week requires a subscription in order to read their articles.

 

I don't think selecting FLCH in final approach is fine however. I honestly don't understand what they were trying to achieve. FLCH won't make the aircraft descend to regain the G/S, quite the contrary, it will almost level out while the speed comes down to 152 (see min, 1:57), at least if you have the target altitude set to runway elevation, which was not the case.

 

If the Autopilot is disengaged but the F/D is STILL in FLCH CLIMB mode (they had the missed approach altitude in the window), the AT will CONTINUE to be in THR mode, as you can see in the video. The plane thinks that the pilot is intending to climb to 3000 feet. Only once the pilot held the thrust levers back, for some reason I don't understand, FLCH kind of "accepts it and surrenders" and reverts to HOLD. But it's still in CLIMB mode, see 2:10 that the pitch bar of the F/D is commanding nose up.

 

Now they apparently disconnected ONE of the F/Ds because somehow they realised they didn't want to climb. But to reset the system you have to turn BOTH F/Ds off. I don't know if this is a thing of the NTSB reproduction or not, I don't know if they show the PFD from the PF or from the PM.

 

The question now is: What sense does it make to have FLCH in CLIMB mode with AT's in HOLD? It's completely messed up.

 
Without being a Boeing engineer and at the risk of saying something that doesn't make any sense because of reasons XYZ, what "I" would have done is the following: When FLCH is engaged in a climb mode, and the thrust levers are held back, effectively inhibiting FLCH from doing "its job", the system should EITHER continue to be in THR mode and bring the levers back up as soon as the pilot releases OR reverting to THR HOLD and crossing the FLCH flag on the FMA with an amber bar as in: "FLCH is not able of performing its mission". The pilot would immediately notice (hopefully) that something is going wrong.
 
This is nothing "new". It happens when in ALT HOLD mode with A/Ts disengaged AND disarmed, at idle thrust and speed slowing down around halfway down the amber bar. At this point the system will say "to hell with altitude" and will let the aircraft descend to prevent it from stalling. On the FMA the green ALT mode will be crossed out with an amber bar.

 

 

ignoring the FMA the whole time apparently.

 

Ignoring the FMA indeed, but more importantly, ignoring their speed which is MUCH worse! Once the AIRSPEED LOW warning triggered, it took them 4 seconds (!!!) to react to this alert, and it was the PM who reacted.

 

This was an unstabilized approach from the very beginning. Being 5 nm out, at 180 knots, thrust at idle, flaps 5 and to further complicate it, well above the G/S, they were doomed from the very start.

 

Oddly enough, I flew on the 777 the other day to ESSA. The same happened to me, with the difference that I was on the G/S. I had to go-around and try it again because there was no way I could stabilize the approach by the mile 3.

Why would you even press the FLCH button on final approach? That seems like a very bad idea to me.

 

Indeed. As I said, what where they trying to accomplish with that? Remains a mystery to me.

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I was doing the same as the video, selecting FLCH initiated a climb, I disconnected the Autopilot and pushed the nose down and started a descent. I pressed F1 to close the throttles expecting HOLD mode, but I stayed in SPD and the throttles would power up automatically to regain required thrust.

 

Hardware throttles?

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By the way, I went and tried it myself and it didn't work, i.e., the ATs wouldn't revert back to HOLD upon manually retarding the levers when in THR | FLCH CLIMB mode.

 

For this to work however, the option "A/T MANUAL OVERRIDE" must be in ALWAYS. Otherwise it will ignore the hardware in any mode other than HOLD. Remember we are trying to force the AT into HOLD by manually closing the throttles while in THR and FLCH.

 

I've been looking closer and MAYBE this has to do with not being able to FULLY CLOSE the throttles via a manual override. They want to stand right up again. Hardware is Saitek X52.

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Hardware throttles?

Idle, and Setting is A/T Overide In Hold Mode only. I see Alpha Floors post, looks like the setting for the throttle has to be in "Always"

By the way, I went and tried it myself and it didn't work, i.e., the ATs wouldn't revert back to HOLD upon manually retarding the levers when in THR | FLCH CLIMB mode.

 

For this to work however, the option "A/T MANUAL OVERRIDE" must be in ALWAYS. Otherwise it will ignore the hardware in any mode other than HOLD. Remember we are trying to force the AT into HOLD by manually closing the throttles while in THR and FLCH.

 

I've been looking closer and MAYBE this has to do with not being able to FULLY CLOSE the throttles via a manual override. They want to stand right up again. Hardware is Saitek X52.

I will try that setup tomorrow and see how that works.

Thanks

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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

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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...

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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

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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 (!!!)

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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"?

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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.

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...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.

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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...

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