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Tristan Marchent

747 V3 TOGA Press Delay

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Is this 'delay' only found on GE engines? I have a vague idea of what you're talking about and I believe it's ony encountered on 747s with GEs, but I don't have a source to support that.

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Not something I've heard of. My closest experience to the real thing is in 747-400 full flight simulators (GE and RR power) but I don't recall any simulated delay there, either on takeoff or go-around.
 
Why should there be a delay?
 
Edit:
 
I found this in the FCOM I have
 
"The TO/GA switches are inhibited two seconds after radio altitude decreases
through five feet on landing. TO/GA is enabled again three seconds after radio
altitude increases through five feet for a rejected landing or touch and go.
"

That's the nearest thing to a delay I could find in relation to TO/GA switches

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I know the 747-400 has a delay in setting T/O power when the TOGA button is pressed

 

You know this from actually flying the plane, I assume...?

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You know this from actually flying the plane, I assume...?

I don't know this from flying the plane... but from watching an in cockpit video on youtube, it definitely shows this. But please correct me if I'm wrong?

 

https://youtu.be/5wjoF8-Oaew (Presses TOGA at 9:06, and there is a slight delay..)

https://youtu.be/2hbQH9J7LWE (Again here at 00:59 seconds, another delay)

 

Are you seeing the same as me? Might be a specific engine...

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ΤΟGA doesnt have any delay. Thats actually its job to set power asap especially on go around manoeuvre or in case of windshear  


I see what you are talking about the servos on the auto throttle. Thats different than the actual toga mode which is instantly visible on the FMA as THR REF or THR (in case of go around) mode. On both cases the engines are already spooled  up before the toga application that has to do with the servos on the autothrottle. Remember that this is irrelevant because the thrust on the 744 is fly by wire and fully controlled by the eec 

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I seem to recall one second from pressing the switches to THR REF and another second from then to the thrust levers actually moving. At least on the ground setting takeoff thrust, no idea about the go around.

 

(RR engines).

 

Why? I can give you no rational idea, and not sure it's in the books anywhere either. But I am 99.9% confident that is what the real aeroplane does.

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On both cases the engines are already spooled  up before the toga application that has to do with the servos on the autothrottle. Remember that this is irrelevant because the thrust on the 744 is fly by wire and fully controlled by the eec 

The Autothrottle servos still are in the loop, EEC or no EEC. Anyway a delay in activating the servo isn't exactly desirable (you certainly wouldn't want that on a go around).

 

In the first video (KLM, GE engines) THR REF is annunciated as soon as the captain operates the TOGA switch. If there is a delay in the aircraft I've never noticed it in the sim (which use aircraft parts for the servos and clutches). However he could be holding the throttles momentarily against the servo,

 

Why hold the levers back? There is only one servo for all four thrust levers, each lever has a slipping clutch. If one of the clutches fails you could get asymmetric takeoff power so it might be wise to hold the levers until all four start to move, Just a theory, mind you.

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Hmm interesting.

 

In the first video listed, if you listen carefully you can hear the movement of the throttle coincides with the sound of the servo's.

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Hmm interesting.

 

In the first video listed, if you listen carefully you can hear the movement of the throttle coincides with the sound of the servo's.

You can't hear the servo in the cockpit. What you hear as the throttles move is the whine of the CF-6s spooling up.

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There's a definite delay between "THR REF" annunciation and the throttles moving forward in both videos.

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On takeoff, up until the point the TOGA buttons are pressed the servos have been disconnected whereas on go around the response of the throttles may be quicker due to servo already being connected. Just a theory...

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I'm sceptical that this is related to a specific engine. Qantas' 744s are equipped with RR's on the OJ* series frames, and KLM appears to use the CF6 fleetwide. 

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