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Autothrottle Hold Mode

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Hi fellow simmers !

 

I'd like to know about some impressions of  PMDG 777' s Autohtrottle behave when in Hold Mode. Please the intention here is discuss only based on last paragraph on PMDG FTCOM page 99.

 

I think any serious simmer would like to test this and colaboratte with SP that has comming..... and I hope that be soon.

 

Best of all,

 

Marco Aurélio

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I've been wondering about the HOLD mode as well, but at the other end of the flight. The paragraph on p. 99 that Marco cited refers to its use during takeoff. I'd like to know more about the HOLD mode during approach and landing, especially with the release of the NTSB report on the Asiana 214 accident at KSFO. (As most of you probably have heard, Boeing is held at fault to some degree in 4 of the 40 specific findings.) How accurately does the PMDG model reflect the real-world functionality of the autothrottles in FLCH mode during approach?

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HOLD works the same as the real aircraft.  The only time you want to see it on the FMA  is during the take off roll or in descent with the throttle at ilde.

 

It should never be a factor in final approach or during landing, except if you screw up like the guy's at Asiana.  

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how did the Asiana crew manage to get into hold mode on final approach?!

They were cleared for a visual approach, which appears to have spooked them.

 

During the approach phase the PIC first used V/S, and then below 3000 feet  used LVL CHG! The aircraft naturally started to climb to the 3000 feet MA altitude they had dialed in. So the A/P was disconnected and the throttles manually moved to idle to reduce the thrust. The A/T was still armed.

 

As they approached the runway the PIC did not notice that the A/T was not commanding speed. He was not aware he had put it into HOLD mode when he reduced thrust to idle.

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how did the Asiana crew manage to get into hold mode on final approach?!

 

They reverted from V/S to FLCH on final with the flight directors on. The MCP had the missed approach altitude set & so the flight directors commanded a climb, the pilot flying then disengaged the autopilot ignored the flight directors and forced the nose down, thrust was already at idle and the A/T went to HOLD.   

 

Bottom line is don't touch FLCH on final approach,  I would be very surprised if Asiana instructs their pilots to do otherwise.

 

Note to Peter -  thrust was already at idle way before they selected FLCH

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AT went to HOLD as the AT system was commanding THR REF and detected the pilot pull the thrust levers to idle. This caused the AT to go to HOLD mode.

 

Best regards,

Robin.

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wow what a crazy approach, why isn't it possible to land using ILS if you are cleared for a visual approach? Why do they sometimes clear for visual or ILS?

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wow what a crazy approach, why isn't it possible to land using ILS if you are cleared for a visual approach? Why do they sometimes clear for visual or ILS?

 

 The ILS was under maintenance so not an option, the localizer & PAPI was available.  Only a visual or non precision  RNAV approach to 28L was available .

 

btw, you still use the ILS on a visual approach if it's available.

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wow what a crazy approach, why isn't it possible to land using ILS if you are cleared for a visual approach? Why do they sometimes clear for visual or ILS?

I think the ILS was not working and hadn't for a little while.

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why isn't it possible to land using ILS if you are cleared for a visual approach?

 

It is, but if I recall correctly the G/S was NOTAMed out of service that day (people also said the PAPI was out, too, but they saw the NOTAM after the accident...which was added because the plane hit it...)

 

 

 


Why do they sometimes clear for visual or ILS?

 

If it's a clear day, you're getting the visual.  It's all about throughput.  With visuals, if the plane ahead of you calls the field in sight, I can ask if you see the traffic ahead (not even the field), and if you have the traffic, I can clear you for the visual approach.  Additionally, if I clear you via the ILS - even if you're in visual conditions - if you lost comms and had to go around at the same time, you'd be flying the published missed.  If that published missed puts you across the paths of the other runways, that could cause issues.  Rare, but the entire IFR system is predicated on always accounting for lost comms.  This is why some ILS approaches are listed as CONVERGING - it's the same ILS approach as the "basic" one, but has different missed procedures to ensure the paths avoid each other (example: IAD Converging ILS R12 and Converging ILS 19L/C/R).

 

More info?

Go here: http://www.fly.faa.gov/ois/

...and open up West Directory (on the left) > ZDV > DEN.

 

Note that DEN's max throughput in fully VMC conditions, using runways 35L|35R|16R|16L for arrivals, can get up to 152 aircraft per hour.  That's achieved because visual approaches place separation requirements on the pilots.  Otherwise, the controllers would need to keep 3 miles between the aircraft.

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There's a very good animation from the NTSB on the youtubes. 


 


Not wanting to start a debate or anything, but had the 777 had the signature Airbus alpha-floor, flight envelope protection, I believe we wouldn't have had a crash.


 


Both Airbus and Boeing philosophies have their own ups and downs. On one hand, hard flight envelope protection would've saved this aircraft, on the other hand pilots would become complacent and begin depending on flight envelope protection (Air France A330).


 


I agree the pilot's didn't understand the airplane, and were primarily at fault for this incident. The fact that he pushed flight level change, and then seconds later disconnected the autopilot is just unbelievable. A simple act of switching autopilot modes for really no reason caused this. Of course a continuous scan of cockpit instruments should've picked up on the error.


 


I think the NTSB made a great call by recommending airline procedures instruct pilots to switch off flight directors when not following them. Perhaps Boeing should consider changing the "HOLD" phraseology to something along the lines of "MAN" for manual, since it could easily be interpreted as "Holding Airspeed".

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Not wanting to start a debate or anything, but had the 777 had the signature Airbus alpha-floor, flight envelope protection, I believe we wouldn't have had a crash.

 

Perhaps Boeing should consider changing the "HOLD" phraseology to something along the lines of "MAN" for manual, since it could easily be interpreted as "Holding Airspeed".

 

Confusion of what the term "HOLD" means didn't play any role in this though according to the report. I don't think they even noticed the mode change honestly. The captain never should have hit FLCH in the first place and he never should have done it without calling out the mode change he was making verbally so that the other pilot was aware and could potentially correct it. The instructor pilot stated he never even noticed it (he was busy extending flaps or something at the time it was pressed). The captain very clearly didn't understand what he was commanding the AFDS to do in a much wider sense given that he commanded a climb at 1500 feet on an approach.

 

Regarding low speed protection, the issue as Boeing's chief test pilot and engineer described it at the hearing made a ton of sense to me - namely that doing so would violate two of their core principles.

 

1. The AFDS system can't have two controllers/inputs to the same primary flight parameter. FLCH is a pitch for speed or "speed on elevator" mode - if the AT kicked in while in this mode, you'd have both thrust and pitch controlling the airspeed parameter. That creates problems algorithm wise (PID instability, instability in a single engine thrust asymmetry situation etc) and it violates the design principle.

 

2. To mitigate #1 above, it would need to trigger a pitch mode change to a speed on throttle mode such as V/S, ALT, VNAV PTH etc as well. One of Boeing's other core design philosophies is that the pilot has control and AFDS modes should not change without the pilot commanding them to. When the captain held the thrust back against the motion of the AT servos as it tried to climb, this is effectively the same thing as moving the yoke while AP CMD is active. It tells the system "I want manual control." That's what HOLD is - it disconnects the AT servo and gives the pilot manual control. You'd have both the pitch and thrust modes changing on their own without pilot command and that's just not what Boeing does. If a pilot is just pressing buttons and moving controls without any regard for what those commands do *and* is incapable of properly handflying the aircraft after disconnecting the automatics, then that pilot shouldn't be in the cockpit, period. Blaming Boeing is totally obfuscating the true cause - lack of understanding of the airplane's systems and really, lack of basic piloting skills.

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Confusion of what the term "HOLD" means didn't play any role in this though according to the report. The captain never should have hit FLCH in the first place and he never should have done it without calling out the mode change he was making verbally so that the other pilot was aware and could potentially correct it. The instructor pilot stated he never even noticed it (he was busy extending flaps or something at the time it was pressed). The captain very clearly didn't understand what he was commanding the AFDS to do in a much wider sense given that he commanded a climb at 1500 feet on an approach.

 

Regarding low speed protection, the issue as Boeing's chief test pilot and engineer described it at the hearing made a ton of sense to me - namely that doing so would violate two of their core principles.

 

1. The AFDS system can't have two controllers/inputs to the same primary flight parameter. FLCH is a pitch for speed or "speed on elevator" mode - if the AT kicked in while in this mode, you'd have both thrust and pitch controlling the airspeed parameter. That creates problems algorithm wise (PID instability, instability in a single engine thrust asymmetry situation etc) and it violates the design principle.

 

2. To mitigate #1 above, it would need to trigger a pitch mode change to a speed on throttle mode such as V/S, ALT, VNAV PTH etc as well. One of Boeing's other core design philosophies is that the pilot has control and AFDS modes should not change without the pilot commanding them to. When the captain held the thrust back against the motion of the AT servos as it tried to climb, this is effectively the same thing as moving the yoke while AP CMD is active. It tells the system "I want manual control." That's what HOLD is - it disconnects the AT servo and gives the pilot manual control. You'd have both the pitch and thrust modes changing on their own without pilot command and that's just not what Boeing does. If a pilot is just pressing buttons and moving controls without any regard for what those commands do *and* is incapable of properly handflying the aircraft after disconnecting the automatics, then that pilot shouldn't be in the cockpit, period. Blaming Boeing is totally obfuscating the true cause - lack of understanding of the airplane's systems and really, lack of basic piloting skills.

 

Fantastic comments Ryan and well summarised. Some general observations which may assist with people understanding the incident:

 

1. The differing design philosophy between Boeing and Airbus. Many people have overlooked the fact that the Asiana PIC had just transitioned off the A320 and had 33 hours on the B777. FBW has been a factor in many incidents globally and as identified, there was an over reliance on automated systems in the Asiana accident.

 

2. Korean culture (and military rank) has been a component in many incidents/accidents (though has greatly improved in recent years). Three out of the four pilots were ex Air Force - the PF had no military background. The PF was 'Ab Initio' trained by the Company.

 

3. The PF was an experienced pilot and ex instructor on the A320, though he hadn't flown into SFO for almost 10 years.

 

Everyone can get rusty, but like you state above, the complete lack of understanding of the systems, poor basic airmanship and poor CRM are the true causal factors of the incident.

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Thanks all of you for healthy comments....

 

Hold is one of the modes in Autothrottle system.....As you said it can appear on take-off or in descents.....When this happen the autothrottle servos stop to work and Thrust levers remain in some position while pilot not interfere...this allows the pilot to adjust the thrust without disengage the autothrottle.

 

Ok......

 

The main utility of HOLD mode is on take-off.... (after 80 Knots) before or  after lift-off the pilot can adjust the thrust. It's a great resource to tame down the bird ......and comply with some noise abatment procedure , ADD MUCH MORE PLEASURE ON TAKE - OFF and perform tight turns in SIDs.more realistically without a huge G force (passengers aren't like goods)....This kind of airliner is highly automated and the pilot has few chances to  " Pilotage ".

 

My question is : Does PMDG service pack will fix the way how it is presently modeled ?

 

The next time I will show a short video demonstrating the present state-of-art.

 

Once more...my intention is collaborate with the SP that has comming.

 

What a wonderful simmers's community !.... Congratulations to all

 

See you soon.

 

Please don't stop to put comments !

 

 

By the way I'd like to congratulate  Kyle Rodgers...He has been doing a nice job !

 

Thanks for sharing with us ....Kyle Rodgers.

 

 

 

Marco Aurélio

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My question is : Does PMDG service pack will fix the way how it is presently modeled ?

 

Not quite sure what you're assuming is broken that needs to be "fixed"...

 

What am I missing?


 

 


By the way I'd like to congratulate to Kyle Rodgers...He has been doing a nice job !
 
Thanks for sharing with us ....kyle Rodgers.

 

Thanks!

 

...and you're welcome!  :wink:

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My question is : Does PMDG service pack will fix the way how it is presently modeled ?

 

 

 

Considering the release product we currently have models the FLCH correctly.

 

Then yes! it will be fixed in the service pack because it is fixed already in the release version. The changes should be as follows:

1: none

 

yay!

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Dear Marco.

 

Be careful with what some people here in this Forum say and write.  Specially what happened to Asiana. There is a significant difference between having an idea about, and really knowing what happened...

 

Simply, try this in your PMDG 777: 

At any configuration ,with A/P, F/D and A/T engaged,  at 10000 feet, set 0 ( zero ) on the altitude window.  Now press FLCH.  The plane will start to descend, at the commanded speed ( bug speed ). The FMA initially will be  THR I xxx I FLCH . Soon after the throttles reach idle, the HOLD mode will replace the THR mode . So far, so good...

 

While descending, disconnect the A/P and disconnect ONLY your side F/D ( leave the other F/D ON ).  Now, start pulling the yoke for a level flight ( or a shallow descend ), and allow the speed to reduce into the yellow band.  Half way into the yellow band, you get EICAS " AIRSPEED LOW" , however, you do not get the A/T " wake up" protection !

 

At this point, if the fellow Korean pilot ( or yourself ) had disconnect the other F/D , the FMA HOLD mode will turn to SPEED mode,  the A/T will "wake up" and the throttles advance to maintain the bug speed. A Beautiful Stall speed protection...

I dont want to extend this talking, but for your info, the correct F/D config for a visual approach, is to have the Pilot Flying and Pilot Monitoring OFF ( in this sequence ), then Pilot Monitoring ( only ) selected to ON. This is to avoid losing the stall protection in case of a Go Around. FCTM 5.45 , 5.54

 

Conclusion: should the pilots had follow the Boeing FCTM , the outcome certainly was a normal landing.

 

Vpira

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Dear Marco.

 

Be careful with what some people here in this Forum say and write.  Specially what happened to Asiana. There is a significant difference between having an idea about, and really knowing what happened...

 

Simply, try this in your PMDG 777: 

At any configuration ,with A/P, F/D and A/T engaged,  at 10000 feet, set 0 ( zero ) on the altitude window.  Now press FLCH.  The plane will start to descend, at the commanded speed ( bug speed ). The FMA initially will be  THR I xxx I FLCH . Soon after the throttles reach idle, the HOLD mode will replace the THR mode . So far, so good...

 

While descending, disconnect the A/P and disconnect ONLY your side F/D ( leave the other F/D ON ).  Now, start pulling the yoke for a level flight ( or a shallow descend ), and allow the speed to reduce into the yellow band.  Half way into the yellow band, you get EICAS " AIRSPEED LOW" , however, you do not get the A/T " wake up" protection !

 

At this point, if the fellow Korean pilot ( or yourself ) had disconnect the other F/D , the FMA HOLD mode will turn to SPEED mode,  the A/T will "wake up" and the throttles advance to maintain the bug speed. A Beautiful Stall speed protection...

I dont want to extend this talking, but for your info, the correct F/D config for a visual approach, is to have the Pilot Flying and Pilot Monitoring OFF ( in this sequence ), then Pilot Monitoring ( only ) selected to ON. This is to avoid losing the stall protection in case of a Go Around. FCTM 5.45 , 5.54

 

Conclusion: should the pilots had follow the Boeing FCTM , the outcome certainly was a normal landing.

 

Vpira

 Ok ..fellow !

 

Seems that I haven't explained clearly.

 

I was thinking and talking only at take-off...try to examine with more attention and may be you can see what I've been tried to explain. To simplify : the Hold mode in takeoff changes.at 400 ft AGL to Thrust Reference Mode without any change to Vnav or other vertical mode... please read FCTM last paragraph on page 99. 

 

Thanks so much for your attention.

 

Best of all.

 

Marco Aurélio.

Not quite sure what you're assuming is broken that needs to be "fixed"...

 

What am I missing?

 

 

 

Thanks!

 

...and you're welcome!  :wink:

Hi Kyle

 

See the post above !

 

 

Thanks,

 

 

Marco Aurélio

Considering the release product we currently have models the FLCH correctly.

 

Then yes! it will be fixed in the service pack because it is fixed already in the release version. The changes should be as follows:

1: none

 

yay!

 

 

  Thanks hopskip ! Ah...Ah....

 

 

Marco Aurélio

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I was thinking and talking only at take-off...try to examine with more attention and may be you can see what I've been tried to explain. To simplify : the Hold mode in takeoff changes.at 400 ft AGL to Thrust Reference Mode without any change to Vnav or other vertical mode... please read FCTM last paragraph on page 99.

 

While I applaud you for looking into the manuals, you always have to remember that the FCTM is somewhat summarized when compared to the FCOMs.  The FCOMs go into greater detail, and as such, are the true reference material for where you'd want to go to confirm or question the correct operation of the aircraft.

 

FCOMv2 4.20.10 goes into more detail, but the basic explanation of what you're seeing is:

Hitting TO/GA selects THR REF as the thrust mode.  That is overridden by HOLD at 80 knots.  VNAV automatically kicks in at 400', unless you hit TO/GA again after 50 knots.  Since VNAV automatically kicks in at 400', THR REF resumes as the active thrust mode.

 

What you're seeing is the proper behavior.

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I was thinking and talking only at take-off...try to examine with more attention and may be you can see what I've been tried to explain. To simplify : the Hold mode in takeoff changes.at 400 ft AGL to Thrust Reference Mode without any change to Vnav or other vertical mode... please read FCTM last paragraph on page 99.

 

Hi, Marco,

 

I think you  may be misreading "VNAV engagement" to mean "pilot engages VNAV."  VNAV is normally armed on the ground and "engages" automatically at 400 ft.  At that time thrust mode switches out of HOLD to another mode - normally to THRUST REF.  Take a look at FCTM "Pitch Modes," FCTM p. 322.

 

Mike

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Hi Kyle,

 

No !

 

I'm not using VNAV at takeoff.. I'm just using TO/GA and LNAV ....nor Auto Pilot.

 

Your last paragraph is correct and I understand what you are saying !

 

Thanks.

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No !
 
I'm not using VNAV at takeoff..

 

I never said you have to.  Read 4.20.10.

 

It never mentions a single thing about pre-arming VNAV at all.  It is automatic unless cancelled by hitting TO/GA after 50 knots.  Autopilot is also irrelevant to the discussion, because ON or OFF, you're going to get the same behavior.

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Hi, Marco,

 

Since you cited a paragraph in the FCTM on p. 99 that is discussing VNAV and Autothrottle transition out of HOLD, I thought you were using VNAV.  However the wording of the FCTM is a bit misleading.  It says that HOLD mode "remains engaged until VNAV engagement or another thrust mode is selected."  This implies that, if VNAV is not selected, the pilot must intervene to "select" another thrust mode when in fact THR REF is automatically selected in most circumstances.

 

Mike

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Hi, Marco,

 

Since you cited a paragraph in the FCTM on p. 99 that is discussing VNAV and Autothrottle transition out of HOLD, I thought you were using VNAV.  However the wording of the FCTM is a bit misleading.  It says that HOLD mode "remains engaged until VNAV engagement or another thrust mode is selected."  This implies that, if VNAV is not selected, the pilot must intervene to "select" another thrust mode when in fact THR REF is automatically selected in most circumstances.

 

Mike

Thanks Mike777 .....

 

 

I'm editing a video to show one take-off from LPPT to LPMA... and a Landing as well showing some characteristics of this outstanding PMDG Product. Please i'd like to hear your comments after you have the patience to watching it.

 

Again...my intention is only share some pleasure moments with other simmers.

 

Best of all,

 

Marco Aurélio

I never said you have to.  Read 4.20.10.

 

It never mentions a single thing about pre-arming VNAV at all.  It is automatic unless cancelled by hitting TO/GA after 50 knots.  Autopilot is also irrelevant to the discussion, because ON or OFF, you're going to get the same behavior.

You're 100 % right Kyle !

 

Please don't get me wrong...But at the end of this discussiion all of us will learn more about this outstanding Arliner.

 

And I have some new question about it like Ground Effect...and others. Of course not here but at another thread.

 

Kyle...my intention is collaborate only.

 

Best of all,

 

Marco Aurélio

 

 

 

Thanks.

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