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oscayala

Over-speed after take-off

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Hello friends:

After over 25 years in simulation, I just purchased it and I am really excited about this new PMDG toy.

I am experiencing an issue after take off. Both flight directors are on, proper flap settings and stab trim, all the FMC settings done correctly, L nav armed, V nav armed, Auto throttles armed, some de-rate power set, V2 set in the MCP and TOGA switch pressed. The speeds and acceleration on the runway are correct and the take-off is nice and gentle, but after positive rate of climb and gear up, the airspeed increases extremely fast and instead of maintain V2 + 10 or V2 + 20, goes quickly until 250, 270 or more in few seconds and sounds the over-speed alarm.

Am I doing something wrong?  I appreciate your comments.

Best regards and happy flights.

 

Oscayala

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Frooglesim actually mentions this in his "Fully loaded part 2" video. It seems to be a known issue that after take off, because of the sheer siZe of the engines that when flying light, the aircraft isn't staying within the 250kts/10000ft restriction.

 

A quick fix that Froogle mentions in his video, and that I have been using myself, is on the FMC s VNAV page, add an extra restriction in of 230kts/8000ft. You will most likely break this new restriction, but you should stay below 250kts while under 10000ft.

 

Luke Cantrill

Fly UK - Cargo Operations

 

 

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I don't think it's a bug or something. I noticed it to. Then I remembered the tutorial where it says to 'push your throttles fully forward' after THR REF annunciation. (page 0.00.63, second bullit). I noticed the next flight that the A/T is on HOLD on that instant, and I have A/T override set to 'only on Hold'. That means that, when a thrust setting of for example 92% (A/T from the FMC), full throttle overrides that setting, resulting in to much thrust and therefore overspeed.

In stead of full trottle your throttle setting after TO GA and THR REF is supposed to be matched with the programmed thrust. The small arrows on the N1 indicators have to align with the blue line of your physical trottles position.

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This sound to me like you're doing a light flight, low ZFW and/or little fuel in comparison to what this plane can really do.

 

I haven't had this problem, but all my flights have been over 13 hours with 600,000lbs+ GW with ZFW around 420,000lbs+... And even then she still has plenty power to almost shoot through speed restrictions.

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I've experienced this problem also.

 

It seems that the MCP set speed is being ignored after take-off. I've even tried pressing the rotary Speed dial on the MCP just after take-off to see if that has the desired effect.

 

NB: I've been using SHORT fuel loads (predetermined by the FMS) for short 60-90 min hops.

 

It's not a huge issue, but I'm interested to know why the 777 does this as opposed to other Boeings.

 

Rgds,

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Derate your engines if light. I'm talking serious derates like TO-2 with a 65C assumed temp. These engines are incredibly powerful and it will do that in the real thing too - you can't pitch fast enough to stop the acceleration just after liftoff at full thrust without risking a tailstrike.

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I have mostly done "light" takeoffs so far and my speed after T/O stays within reasonable margins of the magenta speed.

 

Try setting your hardware throttles to "NEVER" (never override A/T) in the T7 options.

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Guys I think Ryan has pretty much covered it, at light weights you use full derated take off & climb power, combine with the highest assumed temperature you can get away with. Also consider using FLCH on departure, the aircraft will use pitch to maintain speed.

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Guys I think Ryan has pretty much covered it, at light weights you use full derated take off & climb power, combine with the highest assumed temperature you can get away with. Also consider using FLCH on departure, the aircraft will use pitch to maintain speed.

That sounds very accurate, I like it. May i ask though...where can I find the assumed temps I can use?

 

Thanks,

 

Luke Cantrill

Fly UK - Cargo Operations

 

 

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That sounds very accurate, I like it. May i ask though...where can I find the assumed temps I can use?

 

Thanks,

 

Luke Cantrill

Fly UK - Cargo Operations

Unfortunately I don't think the TOPCAT calculations are ready yet, theirs a post on here to a freeware 777 calculator, I have forgotten the name, will do a search online for you.

 

Just be advised the freeware calculator does not respect obstacle limits, also never cancel the derate unless above V2+20 in the event of an engine failure

 

EDIT - do a search on The Avsim library for UTOPIA.

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Rob, if I may ask a silly question, if I use FLCH, do I need just Lnav selected for take off ?

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Thanks FLEX!

 

Will check out Utopia. I have PFPX already, but don't yet have TOPCAT, might have to invest in it for when the T7 figures are supported.

 

Thanks,

 

Luke Cantrill

Fly UK - Cargo Operations

 

 

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Rob, if I may ask a silly question, if I use FLCH, do I need just Lnav selected for take off ?

Hi Julian, you could still keep VNAV armed if the aircraft is using a full derate combined with an assumed temp, the aircraft in theory should remain manageable, but you obviously have the option to switch to FLCH at any time. Just remember that FLCH will bust any alt restriction in the SID so make sure your MCP altitude limits are setup correctly! As always use all the tools at your disposal.

 

@ Luke, definitely get TOPCAT when the 777 profile comes out, I couldn't imagine flying without it, it's just like the onboard laptop performance software flight crews use for Take off & landing data.

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Rob, if I may ask a silly question, if I use FLCH, do I need just Lnav selected for take off ?

 

 

You can arm LNAV prior to T/O, use HDG SEL, engage LNAV manually after T/O - it all works with FLCH as well!

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Thanks Rob.About to do a departure out of Dubai, so will try it. Thanks for your help. BTW, I agree with your comment regarding Topcat. I am really missing using it, so hopefully soon.

 

Edit Thanks Olli

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Thanks Rob.About to do a departure out of Dubai, so will try it. Thanks for your help. BTW, I agree with your comment regarding Topcat. I am really missing using it, so hopefully soon.

 

Edit Thanks Olli

 

Temps @ DBX are already 63c.  Just kidding.

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Temps @ DBX are already 63c.  Just kidding.

Haha, that's a very good point, it is 40c in Dubai this morning if you are using real weather! I am on my way to Doha tonight, not looking forward to it! :/

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So in my scenario I hope you can all help

 

I am doing a manual takeoff so not using lnav or Vnav and just using toga thrust. Once airborne how do I keep the speed minimised as obviously ap is off so I can manually steer the airplane.

 

Thnaks

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Too hot for me. I am use to a cold climate. Glad I can go to Dubai without working up a sweat

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So in my scenario I hope you can all help

I am doing a manual takeoff so not using lnav or Vnav and just using toga thrust. Once airborne how do I keep the speed minimised as obviously ap is off so I can manually steer the airplane.

Thnaks

If you insist on using TOGA your only option is to use pitch to control speed. In reality at light weights you would not use TOGA unless absolutely necessary, even if the runway is contaminated you can still use a derate.

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Aye the chaps covered it. If aircraft is light seriously derate the engines!!! Try it.. Put in no load with light fuel, take off with no derate and you will quickly find yourself at FL*rediculous* and too fast for the flaps!

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You don't need TOPCAT or Utopia to work out your assumed temp. All the data you need is in the FCOM (under Vol 1, Performance Dispatch). I think James White did a tutorial on this in this forum a few weeks ago. I'll also be doing a video tutorial soon.

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David, the FCOM doesn't give you runway specific data, they are just balanced v speeds hence why we are all waiting for TOPCAT.

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Aurasim also is developing a take-off/landing performance calculator for the 772LR (like they did for the majestic q400).

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