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StubbinMyToe

777-200 overspeed after takeoff

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On the runway I hit 52% throttle, then engage TOGA,  I rotate as usual, get into a stable climb then engage A/P with LNAV/VNAV.   But almost always the plane will go into overspeed.  I am sure it is something I am (or am not) doing, anyone  have a suggestion?


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After takeing off, are you following the the Flight Director indications? If you do so, you shouldn't get into an overspeed situation.


John Rubens
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Do you manually trim for speed before A/P engagement?

 

Yes, I am used to doing that because even on the NGX I have it set to realistic.

After takeing off, are you following the the Flight Director indications? If you do so, you shouldn't get into an overspeed situation.

 

Not sure what you mean


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Hi,

 

It's simple: you must either pitch up (MUCH!) more, or reduce power. The AP system probably can't react fast enough to the changing conditions, and overspeed results.

 

I'm guessing the aircraft is very lightly loaded.

 

Use all the pitch you need, but be careful not to have a tail strike.

 

If you use max power and the aircraft is empty, then you'll need about 30 degrees of pitch initially, reducing to ~25 degrees, to maintain airspeed.

 

Best regards,

Robin.

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On the Primary Flight Display you have the Flight Director enabled? As soon as you reach Vr speed, you are suppossed to pull back on the stick until your pitch reaches the Flight Directors commanded position.

The tutorial flight describes this much better than I do.


John Rubens
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You don't need the flight director - but you do need an understanding of physics.

 

You can only change one thing: pitch or power. If you want 10 degrees of pitch, then you'll have to reduce power, otherwise you will overspeed. If you want maximum power, then you'll have to increase pitch, otherwise you will overspeed.

 

Best regards,

Robin.

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I actually had the same problem several times. I did same takeoffs from same airports, same load and everything. I did 6 takeoffs and  3 of those were wit overspeed. Two times N1 was exceeded even on takeoff roll. All settings were normal. 


Edward

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If you are engaging AP in VNAV/LNAV mode, make sure to review the speeds set for the first few SID waypoints. Often a SID will have rather high speeds at waypoints very close to the departure runway (speeds of 220Kts for eg), and if you engage AP with VNAV, it will rapidly accelerate to those waypoint speeds before you have any time to clean up flaps. Reduce these by entering speeds closer to your V2 speed (I use V2+20kts at the first waypoint) to stop VNAV overshooting your flap speeds.

 

And use derated thrust for takeoffs, especially when lightly loaded.

 

Rob


Robin Harris
 

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I limited my speeds for the first three waypoints down from 250 to 200 but still get overspeed.  I don't get it, the plane is perfectly trimmed before I engage A/P.   The plane was fully loaded PAX wise and about 50% cargo.  Fuel was set using short setting,    Sometimes, but not always, the FMC will give me a message saying that the default takeoff speeds were deleted (or something similar).

 

I've been flying the PMDG 737 for a long time, and basically I am using the same procedure to setup the 777 for takeoff, but with different parameters obviously.   But this plane is cruising like mad, by the second waypoint in the SID it is almost 300 knots even though the speeds are limited in the FMC.  After a few seconds it slows itself down and recovers.


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I limited my speeds for the first three waypoints down from 250 to 200 but still get overspeed.  I don't get it, the plane is perfectly trimmed before I engage A/P.   The plane was fully loaded PAX wise and about 50% cargo.  Fuel was set using short setting,    Sometimes, but not always, the FMC will give me a message saying that the default takeoff speeds were deleted (or something similar).

 

I've been flying the PMDG 737 for a long time, and basically I am using the same procedure to setup the 777 for takeoff, but with different parameters obviously.   But this plane is cruising like mad, by the second waypoint in the SID it is almost 300 knots even though the speeds are limited in the FMC.  After a few seconds it slows itself down and recovers.

You still haven't confirmed if you're using derated take off or not.

 

Try TO2 and 60 degrees C to start.


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The full takeoff power is designed so that the aircraft can be completely maximum takeoff weight (say, 14+ hours of fuel plus a good load of passengers) and have an engine fail at V1, and still get airborne and climb at a good % (something like 2 to 4% climb ratio) with a single engine.

 

With both engines going with say, 2 hours of fuel on board... you have yourself a rocket ship.

 

Reduce the power using one of the derate systems.

 

Even with a takeoff derate you may need 25 pitch up once positive rate is confirmed.

 

Without topcat, I'd suggest entering a derate assumed temperature of between 40 and 60 degrees so as to reduce the N1% limit down to the mid-90's.


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Trent Hopkinson, 2015 Crewmember of www.mangrove.com.au WorldFlight sim

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