1) commanded EEC TOGA is a typical engine safe value below 100%. O.K., that is normal but actually nothing a PF needs in case of emergency. Disconnecting both EECs on the overhead panel would be too distracting and time consuming...
So perhaps an "emergency power" switch, like it can be seen on e.g. turbo prop floating planes, could safe the day.

 

GA thrust on high-powered under-wing airliners is typically way less than full power. There is one very good reason, which may not be fully applicable to the 777 due to its FBW, but is quite noticeable in for ex. 757 - the engines, as they start producing more power, create a pitch-up force, since they are under the CoG.

This is apparently a contributing factor in recent 735 crash in Kazan. If you visit Simon over at avherald, you will find that even with added thrust, aerodynamic speed stability combined with pitch-up moment meant that the airplane slowed down from 150KIAS pre-GA down to 117 lowest speed - that even with downtrim on stabilizer.

 

For this reason, and also to reduce the risk of GA alt bust, engines on first TOGA press don't spool up to rated thrust, but rather to a thrust that should deliver something like 2000fpm.

 

If you NEED the thrust (say there is, for some reason, an aircraft in front of you and you have to overclimb it, or you found yourself against a mountain, second press of TOGA button should deliver full rated thrust)

Second TOGA push really only applies to Boeings as far as I am aware. Most types I know of give you full rated thrust once you selct TOGA

Indeed - I am talking PMDG products though.

Chaps, could this be an issue of having no approach idle?

 

For example, on the A320 you have two "idles" - ground idle and approach idle. I don't know off-hand if the 777 has the same, but I imagine it does. The reason for this is to ensure the engine is able to get to TOGA power in the required timeframe. On the A320, if you were at ground idle (~20% N1) it takes about 12 seconds to get to TOGA power, whereas at approach idle (~40% N1) it takes approximately half that.

 

If the 777 does indeed have approach idle, is it possible that completely disarming the A/T system also disabled approach idle? I have no 777 documentation to hand so this is purely speculation but maybe some PMDG or 777-rated guys could answer this.

The 777 like most (if not all) airliners have approach idle

What I meant was - did completely disabling the A/T system also disable an automatic approach idle?

A/T status has nothing to do with approach idle.

 

Regards

second press of TOGA button should deliver full rated thrust

 

 

did completely disabling the A/T system also disable an automatic approach idle

RE-EDITED for better understanding:

That sounds interesting. I indeed disarmed A/T, applied manual idle for deceleration  and manual full thrust (limited by EEC) for going around. I  later tried it by pressing TO/GA (only once) which triggers TOGA thrust, illuminates the A/T button and leaves the A/T arm switch in off position.

(737ngx TOGA PB only triggers FD bars when A/T switch only armed)

 

If disarming A/T delivers ground idle on approach the gap would rise, no matter if manual full thrust, derated TOGA or fully rated TOGA (second TOGA button push) is applied. That could be a good explanation!

(I will have to drive the "Autobahn" now for a few hours. So I'll be back...)

 

 

 

I really hope this shear info helps you understand why the 777 with GE90s has what you call "latency". (i like the term, I really do!)

Thank you very much Luc for your very indepth look into the many aspects of possible engine latency. I will go through it very thoroughly as soon as I have adequate time. I really appreciate it!

 

 

Always happy landings (with APPR IDLE!),

Claus

If disarming A/T delivers ground idle on approach...

 

As said above, it doesn't.

 

And as usual, the answers are in the manual if you do a simple search:

 

EEC Idle Selection

The EEC selects minimum idle or approach idle automatically. Minimum idle is a

lower thrust than approach idle. Approach idle is selected in flight if:

• engine anti–ice is operating

• the flaps are commanded to 25 or greater

• one hydraulic system air–driven demand pump is inoperative, and the

flaps are out of the UP position

• the opposite engine bleed air valve is closed

Approach idle decreases acceleration time for go–around. Approach idle is

maintained until after touchdown, when minimum idle is selected.

 

 

With the high gearing analogy I did not mean the ("viscous") connection of N2 to N1. I thought of the difference of transmission effort between small and large diameter fan blades. So a large diameter fan operates on lower RPMs producing the same amunt of thrust as a small diameter fan operating with higher RPMs. Actually like a large tire requires lower engine RPM than a small tire for the same speed on the road. The small tire requires higher engine RPM which results in higher fuel consumption. BUT the small tire can be accelerated easier, as it does not require more torque but higher engine rpm, which is easier to deliver. (reduction, tire on road=effective thrust)
Facit: the large fan diameter delivers fuel efficiency for the price of agility.

The GE90 is no less "agile" than any other high bypass turbofan. As was mentioned earlier by Rob, they have to be as responsive to meet the certification rules. Yes it has a larger fan with more inertia, but the core produces more energy than a smaller turbofan so overall the balance is maintained.

Another thing that's a golden rule in the real world flying side is that this engine "latency" and all these thrust issues for a go around are more directly resolved with flap use rather than JUST the engines thrust (although both are critical). 

 

Your first half of flap movement adds lift, and your second half increases drag (for the 777, that means your first 15 degrees will allow you to slow down, your second 15 degrees will keep slowing you down, but force your engines to run harder to counter the drag)  This in turn means that your most immediate speed increase comes from retracting the flaps on a go-around as the engines SHOULD be running high enough to start giving you a push once that drag is gone even if you haven't speedily pushed the TO/GA button. Then the high engine thrust from cranking the engines does the rest

Hello folks!

 

Thank you very much for all the replies you made on this thread.

I really learned a lot and there were many things quite new to me.

 

But here is something that confused me over the last week:

I stated several times in my posts on this thread that pressing TO/GA triggers FD and Thrust TO/GA , even though the A/T arm switch is in OFF(!) position.

Additionally A/T becomes enganged (green A/T light).

THAT IS ONLY TRUE if you turn the A/T arm switch(es) to OFF from Cold and Dark BEFORE the cockpit gets electrical power (battery/GPU).

 

As I prefer to start the systems and engines without A/T being armed (just a single click could catapult you somewhere...), I always keep the A/T arm switch in OFF position until RWY alignment is obtained for T/O.

 

Because the A/T arm switch of PMDG's T7 is by default ON from cold and dark and the manual states an "always on" policy for this switch, most of you would probably not have noticed this BAD autoflight BEHAVIOUR.

Once again: this only happens if you turn OFF the A/T arm switch before "electricity reaches the cockpit".

In the further course of the flight, the "A/T-arm-in-OFF-position"-switch continues to behave like being actually always "ON". 

This leads to the conclusion, that turning the A/T arm switch(es) from on to off in cold and dark IS NOT RECOGNIZED by the (PMDG) T7 logic. It logically remains in the ON position although it is set physically and visually to OFF...

 

So it's a BUG and not a FEATURE, I think (or hope).

If it is nevertheless a feature, it would be a very dangerous one, because a pilot getting used to a "TO/GA-power-always-there-no-matter-what-the-arm-switch-says"-TO/GA switch could make a big hole in the ground before even noticing that this time something went wrong...

 

Always happy landings,

 

Claus

 

P.S.: I really searched the T7 forum thoroughly for this A/T trouble, but found nothing about it. Probably some PMDG officials could post an answer about this subject?

So thanks in advance...

Sounds like you might have found a bug. The SOP is for the A/T to be left armed so it can automatically engage if necessary, but of course if the switch is off the associated A/T should not engage. This is clearly stated in FCOM Vol 2. Probably best to raise a support ticket about it. There might even be time for a fix to be found for SP1.

 

 

Sounds like you might have found a bug.

I just checked FCOM Vol2. 4.10.4.

It says: with A/T arm switches off all  A/T modes are turned off and their activation is prevented.

 

So I decided to raise a support ticket at PMDG, what I just did.

We will see...

Can you inform us about PMDG answer, please. I'm sure everyone is interested in outcome.