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View Full Version : B777 TO1/TO2 Take-Off Limitation


BMM389EC
18th Sep 2007, 09:09
Hello All
My FCOM says TO1(10%) or TO 2(20%) should be considered a limitation for take-off.Don't advance thrust levers except in an emergency. Vmcg and all that stuff.
Now my question is-when does that no longer apply? Above V2-1.13 x Vs1G in Take -off config. Vmcg no longer a problem(is it?) ?
Or is it later?

SuperRanger
19th Sep 2007, 15:53
windshear?

mutt
19th Sep 2007, 18:30
Its not written, but considering that the problem is directional control you can increase the thrust when you have exceeded VMCG/VMCA for the installed engine, alternatively you can do it anytime as long as you do it slowly and ensure that you maintain directional control.

Mutt

john_tullamarine
19th Sep 2007, 22:49
.. and, if you get caught out ... a bit more bank into the operating motors will lower the Vmc significantly ... won't do much for climb .. but anything (potentially) is better than going in upside down or cartwheeling after digging in a wingtip ...

The effect of bank is quite pronounced .. don't have much quantified data to hand but, as an example and subject to the limitations of my recall over the intervening years, one many-engined military beastie operated by a far off land has something like a 30-40 knot difference between 5 degrees bank one way and the other ...

BuzzBox
20th Sep 2007, 01:20
My understanding is that the limitation is related to Vmcg issues, particularly near V1. Once airborne and above V2 you can safely increase thrust above the fixed derate, all the way up to Max TO if necessary.

Once upon a time we had a note in our 777 Flight Crew Training Manual to that effect. The note has since been removed, but in the sim we still practice increasing thrust in the event of an engine failure. Given the hugely reduced thrust settings we use for most take-offs, the increased thrust following an engine failure provides much better single-engine climb performance.

BMM389EC
20th Sep 2007, 01:53
Agreed-I'd be looking for the improved single engine performance-I also remember there being something written on a previous type that you could safely take it above V2........but have'nt been able to find anything in my Boeing books.
Now that begs the next question-TO 1 take-off with an assumed temperature of say 45 degrees. Airborne and you press the TOGA buttons. Does it delete everything and you've got Max TO, or does it just delete the assumed reduction and leave you with TO 1?

BuzzBox
20th Sep 2007, 03:11
If you push the TO/GA switches after take-off LNAV/VNAV will disarm, TO/GA will engage, ALL derates will be removed and the autothrottle will engage in THR REF.

If you don't push the TO/GA switches and increase thrust by manually advancing the thrust levers, the autothrottle will activate when VNAV engages at 400ft above runway elevation, and set the thrust to the selected take-off thrust setting. That will probably result in a thrust reduction - not what you really need at that point!

john_tullamarine
20th Sep 2007, 06:39
Points to note ..

(a) there should be no need to increase thrust if everything goes according to the gameplan .. as the calculations are predicated on the rules and the thrust ..

(b) if you want to increase, then KNOW the minimum V1/V2 values (for maximum rated thrust) for the conditions .. and respect them

(c) in any case, advance the throttles SLOWLY

(d) unless you happen to be somewhere near limited with the reduced thrust levels, the aircraft generally will go like a cut cat anyway .. and, by the time you get around to thinking about pushing the throttles up .. speed will not be a problem on the ground and you only need to worry about Vmca .. and that WILL bite you if you aren't a bit cautious ...

setvfs
14th Oct 2007, 10:28
For those of you with EFB performance tool if you slect show full this will give you the thrust rating you can advance to while staying within VMCG limits.

To be safe wait until airborne and stable above V2.

mutt
14th Oct 2007, 16:25
Thats interesting......but surely it stays with the same rating?

Mutt

TwinJock
15th Oct 2007, 17:34
Boeing is looking at this, as it has become a problem with a 50% increase in thrust from the 777-200 A market and the B777-200LR. We are waiting for a solution, as it will create a problem if TOGA is selected at low speeds.