ENG FAILURES

[Hardy Heinlin]

If it's clearly documented like this, it must be true, of course.

I have never seen this in any 744 manual in the past 20+ years. I'm really surprised. I'd like to test it in the big sims ...


Cheers,

|-|ardy

[Britjet]

Google "autothrottle wake-up"...

Peter.

[John H Watson]

-Above 100ft Gnd for Approach / Above 400ft Gnd after Takeoff

And what happens if one or more Rad Alts are inop?  :mrgreen:

[Hardy Heinlin]

Google "autothrottle wake-up"...

Thanks. From Google I'm now learning that this is feature is installed on the 747-8 and some 747-400, and that they have been considering installing it on all models as recommended by the FAA in 2011 or 2013 (Asiana accident).

So it looks like it was airline specific in the past? Or it is still optional today?


Cheers,

|-|ardy

[jtsjc1]

I exchanged some emails with Capt. Bill Palmer who wrote the great "Understanding AF447" book and he was saying the FAA wanted this feature to be implemented on the 787 but Boeing refused saying speed protection was not required in any mode for the A/T and the modes in which it worked were "gravy" in his words. He also stated in the Asiana crash (his quotes) " Asiana's procedure of having one FD on and one off is also a problem (and a bad idea). The instructor pilot apparently failed to turn both FD off at the same time before turning his own back on. This would have put the A/T back into speed command mode however since his since his remained on,the autoflight mode remained unchanged and the thrust remained at idle."  He was very interested in that particular accident and I didn't realize that the A/T would remain at idle when switching off one FD. This being a T7 I understand its different than the 744 but if this is implemented to existing a/c I guess it will be the same.

[tango4]

Hi guys,
just coming in the middle of the topic because I already talked about that in another topic and still don't understand everything.
I read the report for the Asiana and if I understood correctly, the reason why there was no AT wake-up was because it was in HOLD mode. And the FD discussion mentioned above was the reason it REMAINED in HOLD mode.
But the reason it transitioned to HOLD mode was the fact that a pilot pushed FLCH with a higher altitude than present which commanded THR REF and immediately after that disengaged AP and pulled back the throttles to idle WITHOUT pushing AT disconnect.
Hardy I remember you told me that it was probably a 777 feature but the discussion  here about AT wake-up on the 747 makes me wonder (I also thought there was no AT wake-up at all on the 747 but it seems it is not the case). The other reason why I think it might be the case on the 747 (and I insist on MIGHT) is because I could not find any reference in the 777 FCOM clearly stating that if you hold the throttles back manually when in THR REF it will transition to HOLD mode.
Any input on that issue from the real pilots on those forum would be much apreciated (although it can wait for a specific British pilot to be back from golf !!).

Just edited for a thing I wrote that was wrong about the fd resets, my bad !

Charles

[Britjet]

BA aircraft have it. We would do a demo of it on conversion courses.
The A/T switch had to be ON, of course, but the mode would be blank.
I wouldn't have thought it would be airline-specific, but I don't know.
I haven't heard of the radalt connection.

The 777 accident was a classic case of being in FLCH HOLD mode, as I understand it. For this situation the 747 won't increase thrust either. Again we would sometimes use this to demo a low altitude stall recovery situation, typically in a tight base turn having selected FLCH..

Peter

[tango4]

Hi Peter and thanks for your answer.
If possible I'd still like a clarification on how to GET FLCH HOLD mode for a CLIMB (by that I mean MCP ALT higher than current ALT at the moment you press the FLCH button, which was the case for the Asiana).
Was my explanation correct ? (Press FLCH then force the throttle to idle, would it make the mode go to HOLD and out of THR REF or is it something else that I missed that caused HOLD mode to engage).
Perhaps that part is 777 specific ??
Thanks again for all your help !

Charles

[Hardy Heinlin]

Here's a demo with VNAV SPD and A/T mode blank. There is no wake-up, just alpha protection keeping the speed at stick shaker speed:

http://youtu.be/IJKU19Rn0GA

PSX behaves in the same way.

However, ... yes ... when VNAV SPD is engaged, the wake-up is inhibited.


Cheers,

|-|ardy

-Above 100ft Gnd for Approach / Above 400ft Gnd after Takeoff

I assume approach 100 is RA, and takeoff 400 refers to the usual barometric elevation record at 100 KIAS.

[Hardy Heinlin]

Wake-up is now available:

http://aerowinx.com/forum/topic.php?id=2637

[Britjet]

Hi Charles,

Not a situation that would readily represent itself ( and I have also flown the 777, but some years ago)  but I think that if you hold the throttles shut it will still resolutely stay in whatever mode it is in - I think that overriding the servos has no effect on the mode..

Peter

[tango4]

Thanks for your answer Peter !
In that case if anyone here is familiar with the Asiana accident and understood how the AT went into HOLD mode I'd be glad because it looks like I'm missing something.
And thanks for beta 5 Hardy  !

[Christo van der Loo]

Not sure if you have seen this...

http://youtu.be/QVaQYhd_Qy0

He did set 3000 while still in V/S and then when he pressed FLCH the airplane obviously wanted to climb. He then then disconnected the AT.

I am not 100% sure but remember being shown that while the thrust levers are moving fowrward in THR REF in the 777 and you physically hold them back the AT will go to HOLD, but as I say. Not 100% sure. Will have to check it out next time in the sim.

Cheers
Chris

[tango4]

Yes I've seen it a hundred times !
Ans as you mentioned the only thing I don't get is why on earth does the THR mode go from THR REF to HOLD !
I've tried it on the PMDG 777 (by holding the F2 key pressed for those familiar with FSX controls), without success. But I don't know if it is because of the way FSX models throttles or because this function does not exist.
So I still have no idea !

Thanks for your answer anyway and if you can try it in a real Sim that would be fantastic !

Charles

[Skybird]

Yes I've seen it a hundred times !
Ans as you mentioned the only thing I don't get is why on earth does the THR mode go from THR REF to HOLD !

Hi Charles,

Shall I try to give an explanation to this?  :roll:
First of all, the FLCH mode is NOT an approach mode. It is generally used by crew as a means of expediting descent towards the required path or when they get confused with the VNAV descent modes. It is an "easy" mode to engage, because it bypasses the whole FMC constrains. However, there are some inconvenient to this mode:
You can't choose your rate of descent (a R/D of 1000ft will be accomplished in 2 minutes!!), and the speed reduction is not anymore managed.
In FLCH, the elevators will move to maintain the speed, and the autothrottle will make the airplane climb or descent
Consequently, when FLCH is engaged, the only mode that could be seen on the FMA are THR or HOLD. In HOLD (the systems is telling the pilot "You have controls"), the PF can increase or decrease thrust to modify the rate of descent (or climb).

[tango4]

Hi Skybird,
Unfortunately I am aware of all that.
What I do not understand is in what situation HOLD mode would engage in a CLIMB.
During descent normal behaviour would be THR and then HOLD when levers reach idle.
In climb, when you press FLCH, AT goes to THR, and stays there until you reach your altitude.
I am totally aware that in the Asiana accident the pilot should not have pressed FLCH. And if I remember correctly the pilot did not even remember pushing it when he was debriefed by the NTSB shortly after the accident.

I really do not understand what caused HOLD mode in this accident (I've seen the NTSB video and read a big part of the report and I still don't get it).
Charles

[tango4]

And this is a quote from the description of the NTSB video for which Chris posted a link a few posts above (click below the video to expand and get full text):

The PF disconnected the A/P and moved the thrust levers to idle, which caused the autothrottle (A/T) to change to the HOLD mode, a mode in which the A/T does not control airspeed.

[Hardy Heinlin]

In FLCH the A/T never controls the airspeed, regardless of HOLD or THR or blank. FLCH is elevators on airspeed, and thrust on vertical speed.

[tango4]

I know that!  I guess I should have made a shorter quote !
The part I'm interested in is : moved the thrust levers to idle, which caused the autothrottle (A/T) to change to the HOLD mode.

Charles

[Britjet]

I have never heard of the autothrottle on the 747 transitioning to hold mode just by being held retarded, but it certainly seems to happen on the 777 according to the NTSB.

Occasionally you might override the rather slow throttle closure in a FLCH descent to get you down quicker, and HOLD would happen anyway after a few seconds, but if this is a result of holding the throttles shut then this is a new one on me. (Which isn't to say it doesn't happen)

I have certainly never seen it done in a climb scenario, which sounds downright dangerous, as happened to the unfortunate Asiana.

Of course, with a full-flight regime autothrottle which the 777 has (ie you keep it in all the time) the pilot doesn't get the exposure to the requirement to monitor thrust on the approach, as is the case for the 747.

When I converted back to the 747 after being on the 777 it took me quite some time to get used to including thrust in my scan..

I am having dinner with some 747 ex-colleagues this evening and will ask them..

Peter