Sign in to follow this  
StubbinMyToe

777-200 overspeed after takeoff

Recommended Posts

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?

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

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

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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. 

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

Nope, was ising the default takeofff rate.  I have yet to get PFPX + Topcat to help me get the info, so I avoided it

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

Last flight I was derated and pushed throttles up to 55%, stabilized and hit TO/GA. After t/o I saw the speed increasing way too quickly. The amount of pitch needed to maintain V2+20 would have been way too much. I attempted to override the mode the plane was in with with some type of SPD intervene on the MCP and couldn't figure it out. Need to work more on it for sure.

Share this post


Link to post
Share on other sites

I have sometimes found my hardware throttles will re-capture in Hold mode (even though I have moved into the null zone), usually resulting in the N1 value busting through the expected derate. Physical Throttles override auto thrust [never] option in the FMC PMDG options can mitigate this, but I have seen it not do that once or twice.

Share this post


Link to post
Share on other sites

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

 

Try TO2 and 60 degrees C to start.

 

That fixed it,  even with the 777-200 full pax and cargo (but not fuel) I guess those engines are just too powerful ;)

Share this post


Link to post
Share on other sites

That fixed it,  even with the 777-200 full pax and cargo (but not fuel) I guess those engines are just too powerful ;)

Glad that helped. Yes those engines are big and you have two of them! Just remember that it was designed to fly with just one engine. B)

Share this post


Link to post
Share on other sites

 

 


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.

 

Are you by any chance having these "rocket" take-offs after loading a saved flight with FMC programmed and all set to go??

 

I saved a flight all set up to go for pushback. This included Takeoff settings (derated thrust settings and Vspeeds), and for the life of me I could not get any control of the speed at takeoff, other than by pitching up very high (6000ft/min climbs). I soon realised she was taking off at full GA thrust, ignoring my TO derates, MCP speed settings, and climb thrust settings (CLB2).

 

Then I saw that "Thrust Ref" was not enunciating on the PFD after selecting TO-GA, and the heading and vertical mode fields on the top line of the PFD both had green "TO" enunciated, instead of the "TO/GA" which are normally there for a derated takeoff (if you see "TO" in these fields you are in for a Cape Kennedy experience). Clearly my takeoff settings were being ignored.

 

So I re-loaded the saved flight and did this;

 

Turn off both "AT/ARM" switches.

Turn off both Flight directors

Change the Takeoff settings on the FMC. I just re-entered the derate temp. You should get the message "Vspeeds deleted"

Accept new Vspeeds

Turn "AT/ARM" switches back on

Turn both Flight directors back on.

 

This time it worked absolutely perfectly, with a nice slow, steady climb-out, and speeds properly managed.

 

Rule seems to be that if you load a saved flight with FMC fully programed, you must re-initiate take-off settings by disarming Autothrottle and Flight Directors, re-affirm TO settings and Vspeeds, and then rearm Autothottle and Flight Directors.

 

Obviously one should not have these problems loading from a cold-and-dark state, or from a saved flight where no FMC programming has been saved.

 

Regards

Rob

Share this post


Link to post
Share on other sites

 

 

the heading and vertical mode fields on the top line of the PFD both had green "TO" enunciated, instead of the "TO/GA"

 

Well that in its own right indicates a problem as it is not possible to get TO as an FMA mode at any time.

 

Best regards,

Robin.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this