I know this topic was probably covered, but I can't find it (I really hate the search function)  Anyway:

 

I never used auto throttles for take off.  But in the 777 full motion sim, the instructor had us set the A/T to take off speed and hit the TOGA button and the plane accelerated to the 145 kts.  At 1000 ft, he had us dial up to say 200 kts and the plane did exactly that.

 

On my sim, If I have the speed set to 145 kts and hit TOGO, or if on the runway and activate the A?T button, the plane indeed accelerates - but it'll keep on going past 300 kts.  It never will back down to the set speed.

 

No once in the air, A/T works perfectly all the way through landing - It is JUST take offs that something is wrong.

 

2 questions:

1.  Is the TOGA generally used for takeoffs?  Or are throttles manually advanced on a 777.  Most Youtube videos show them manually advanced.

 

2.  What am I doing wrong? - VNAV is not selected AP is also not selected . Just A/T.  The speed selection in the FMC is set at 150 KTS also -so why the overshoot.

 

I mean I can easily correct this by manually switching off A/T and reducing the throttles but you over shoot 150 kts very quickly  _ Oh and I have thrust limit set at 20%.

1. Always used (especially on the 777) You manually advance to stabilize the engines then push TOGA

 

2. A V2 of 145 means you are incredibly light.  In fact I don''t think you can have a V2 that low due to Vmca.

 

Anyway, derate thrust & combine it with an assumed temp & CLB 2

 

Also change your thrust reduction height to 800 if the airfield allows it

 

Regards

Oh yes, I am flying very light and V2 is indeed 145 kts.  One more thing, I never set up the speed profile in the FMC.  I thought if I set A/T to 145 kts and hit TOGA I will go to 145 kts - Is that the wrong assumption?

 

So I re-did a flight and did set up speed profile in FMC, I hit TOGA and plane accelerated, this time it wants to settle in at 240 KTS, I set AT speed to 140 KTS, but it automatically chooses 240 kts.

 

How is my 140 KTS over-written to 240 kts?

The aircraft will 'attempt' to maintain the initial target speed until the acceleration altitude. Are you using a derate/assumed temp combination?

 

I would never use full rated thrust at the weights you are describing.  If I was forced to use full rated thrust I would either hand fly raw data with the FD off, accept the huge climb rate to control speed or go straight to FLCH with FD on after I engage the autopilot.

 

These engines are designed to give excellent climb performance at max take off weight. Using max rated thrust at light weights is airshow kinda stuff 

On my sim, If I have the speed set to 145 kts and hit TOGO, or if on the runway and activate the A?T button, the plane indeed accelerates - but it'll keep on going past 300 kts. It never will back down to the set speed.

 

No once in the air, A/T works perfectly all the way through landing - It is JUST take offs that something is wrong.

You need to understand that the autothrottle on takeoff is not in a speed mode. It is setting takeoff thrust. It will not reduce thrust if you exceed the set speed. Speed will be controlled by elevator controlling pitch. If you don't engage autopilot it's up to you to control speed by following flight director commands.

 

Derating thrust won't actually solve your problem, it will reduce acceleration a little and give you more chance to take control.

 

The important thing is to look at the FMA display on the PFD. If the left most annunciation does not say SPD then the autothrottle is controlling thrust.

 

 

Sent from my iPhone using Tapatalk

 

 

You need to understand that the autothrottle on takeoff is not in a speed mode. It is setting takeoff thrust. It will not reduce thrust if you exceed the set speed. Speed will be controlled by elevator controlling pitch. If you don't engage autopilot it's up to you to control speed by following flight director commands.

 

This.

 

You will need to understand the different modes of the A/T besides Speed mode.

 

For the whole first part of the flight, up until first level-off, it will stay in "thrust rating" mode.

 

That means, the autothrottle is selecting appropriate level of maximum thrust. Speed is controlled only by pitch.

 

In TOGA mode, that means, that you should pitch up to keep the speed to 165, then pitch down a bit as climb rating is set. Next step is acceleration, that can happen as soon as at the same precise point, or a bit later on (typical in Europe is 1500ft reduction, 3000ft acceleration)