744 aft CG, lo weight T/O.

[Lemper]

I would like to have the opinionS of Big Lady Riders on this topic.
My fourth Airline on the type, and here is the hick-up:
Two of them IMPOSE, in their SOPs, a static T/O technique for LO WT AFT CG; One RECOMMENDS it, and one RECOMMENDS a rolling T/O techinque.
When I say static, I mean 70% N1 (or 1.1 EPR for PW) on the brakes, release and then push TOGA, and rolling T/O means release brakes first, gently increase to 70% N1 stable then push TOGA.
I have an idea what to do and why, but with age, I start doubting more and more every day.
So, come on guys, unleach your brains and experience.
Thanks

[chemical alli]

here is a number of reasons why said sop are different per same type different engine manufacturer

1.pw4000 increase thrust with brakes on then to toga after rolling due to pw4000 having a nasty stall/surge characteristic at vr due to compressor tip clearance

2.rb211 either will work as the rb engines compressors are built tough but as they age have been told by tech reps that due to heating of compressor and case differential and high tip clearances normal surge or stall will be at approx 200 to 400ft after t/o approx 1min 30 to 2min mark

3. cf6 increase with brakes on then toga the ge is easy to surge with x winds

[Lemper]

Makes sense...Thanks. Now, one operator on a Faraway Island operates both PW and GE, same technique regardless of engine.
More opinions around?

[chemical alli]

Makes sense...Thanks. Now, one operator on a Faraway Island operates both PW and GE, same technique regardless of engine.
More opinions around?
question which sop technique? brakes on /toga or rolling 70%n1 /cf6 or 1.2 epr then toga pw4000 would be interested what sop this far away island hopper uses cheers

[Phil Squares]

Here's our SOP

When taking off at light weight and with an aft CG, the combination of full
thrust, rapid thrust application, and sudden brake release may tend to
pitch the nose up, reducing nosewheel steering effectiveness. With CG at
or near the aft limit, maintain forward pressure on the control column until
80 knots to increase nosewheel steering effectiveness. Above 80 knots,
relax the forward control column pressure to the neutral position. At light
weight and aft CG, use of reduced thrust and rolling takeoff technique is
recommended whenever possible. The rudder becomes effective
between 40 and 60 knots.

Note: Elevator forces for rotation are very nearly the same for all weights
and CG locations.

[Lemper]

Thanks Phil. Comforting, as this is what I have always thought too, however,
I still cannot figure out the rationale behind 1) IMPOSING a technique, whatever it is; [I believed from early english aviation lessons that a procedure was imposed/established/mandatory...and a techinque was recomended];
2) what WOULD be the advantage, with light weight and aft CG, of revving up engines while on the brakes and then releasing them; intuitively (yeah, I know, one should not fly with intuitions....nowadays) I associate that with pushing on the brakes while backing an aircraft (NOT the 747) with reversers.
Not that it gives me mystical anxieties, but I'd like to get informed opinions other than ab-initio brain washed kids with business degree, or retired colonnels who will tell me in shattered English that it is a State Secret.

[john_tullamarine]

Another consideration ..

(a) for low weight and rolling start, the breakaway thrust is comparatively low .. one is some distance down the runway by the time full thrust is set

(b) for high weight and rolling start, the breakaway thrust is high and full thrust is set before the aircraft has progressed any great distance

(c) .. low weight AND limiting distance departure may dictate the sense of holding on brakes initially.

Re pitch up, this can be a problem in excessive tailwinds ... however, if the AFM technique words are heeded, and limitations observed, then one should not need to be too concerned ..

[Lemper]

Thanks John. Makes sense too. However, I wonder if (some) company's SOP makers do read the AFM!

[JammedStab]

I would like to have the opinionS of Big Lady Riders on this topic.
My fourth Airline on the type, and here is the hick-up:
Two of them IMPOSE, in their SOPs, a static T/O technique for LO WT AFT CG; One RECOMMENDS it, and one RECOMMENDS a rolling T/O techinque.
When I say static, I mean 70% N1 (or 1.1 EPR for PW) on the brakes, release and then push TOGA, and rolling T/O means release brakes first, gently increase to 70% N1 stable then push TOGA.
I have an idea what to do and why, but with age, I start doubting more and more every day.
So, come on guys, unleach your brains and experience.
Thanks

Straight from the AFM. I suppose the reasons for the procedure are due to what previous posters stated. I notice that it says release brakes, IF APPLIED. I wonder if some are misinterpreting that as meaning brakes must be applied until 70% N1 is set. Our SOP is a rolling takeoff is recommended but brakes may be applied. Perhaps earlier AFM info was different.

L O W G R O S S W E I G H T, A F T C G T A K E O F F P R O C E D U R E
1. Confirm 15% (or greater) derate thrust for takeoff, or the equivalent using assumed temperature thrust reduction, or the equivalent using fixed derate thrust and assumed temperature thrust reduction.
2. Align airplane with runway centerline. Apply brakes (optional).
3. Advance thrust levers to approximately 70% N1 and allow engines
to stabilize.
4. Release brakes, if applied.
5. Advance thrust levers to preselected takeoff thrust.
6. Input full forward control column deflection to approximately 80 knots to improve nose wheel steering.


The AFM also states in a separate area for any takeoff "With the CG near the aft limit, maintain forward pressure on the control column to approximately 80 knots to increase nosewheel steering effectiveness."

[Intruder]

From our FCOM:
Rapid thrust application combined with an aft CG, light weights, slick surfaces and a rapid brake release, all reduce nose wheel loading. A rolling takeoff is preferred.

[main_dog]

That's what our FCOM Supplementary Procedures recommend too (rolling takeoff): and we operate RB211s, PW4056s and 4062s, and now GEnx-2B67s. Southeast Asian major.

Not sure why a static takeoff could be desirable in this scenario? :confused:

[JammedStab]

Perhaps it is not as rolling is recommended. But if for some reason static is required, release brakes at 70% N1 or equivalent.