jonseagull

Just started flying fixed de-rated 767's and trying to find out why with a de-rated T/O one or two you add +1/2 or +1 units of stab trim yet with an assumed temp derate a/c that could produce the same N1s on T/O, the stab trim is not adjusted.

Any ideas out there ?

Spooky 2

I have never heard of this procedure. Where did you find it?

wobblyprop

Jon,

Does it perhaps have something to do with the reduced thrust pitch couple change resulting from the lower thrust from TO 1/2

Rgds

Wobbers

P.S. Just joined the World of TUI?

Spooky 2

I will go one step further and say that what you have described is not now, nor has it ever been a Boeing procedure. Tribal folklore and nothing more.

wobblyprop

funny, because there are separate stab trim tables in the PI for FULL, TO1 and TO2 say differently. Example TOM 160,000kg MAC TOW 24%

FULL stab = 4
TO1 stab = 4.5
TO2 stab = 5

Spooky 2

Excuse me and my ignorance. I read something into the first post that was not there. I cannot find the data you refer to in the QRH Perf section and that may be because my QRH is not tailored as the one you are using. Can you point to the page and engine model that your using?

Spooky 2

Just a little more for what it's worth. No one in the Boeing 767 program, either technical, training, or performance have ever heard of this policy or procedure so I suspect it does in fact take on somewhat of a tribal technique. the fact that it may work that way in the Perf section of the QRH is nothing more than a coincedince??

penguin22

Here's ABX Air's official tribal technique:

No stab adjustment for Max Power or TO1.
When we use TO2, we add one unit to the trim. I'll dig around and see if I can find any reference as to why.

Veruka Salt

We (Qantas) added half a unit up trim when using assumed temp reduced thrust (RR & GE engines).

jonseagull

How'du guess wobbly !

Spooky, I believe the additions are an amalgamation of the stab trim tables from the PI tables in the QRH. The confusion I have arises from the fact that you can get the same N1 figures via the assumed temp method but we currently don't add the 1/2 or 1 unit.

Could just be a company difference that has not yet been addressed.

shitzig

Hi all,

once i flew with a captain that was asking me to calculate the EPR % reduction we were doing when using the Assumed Temperature Metod (ATM)
so that we could use then the P.I. fixed TO1 or TO2 tables.

for example 1.73 original Epr to 1.60 would mean:
60x100/73= 82% therefore roughly 20% thrust reduction.

i dont know if this is the way because now, going through FCTM, i found boeing treats differently
ATM and Fixed derate metod when to moving thrust levers forward during take off. and i wonder if thats not the reason because there is no trim table for ATM.

ATM:

"the primary thrust setting parameter IS NOT CONSIDERED A LIMITATION.
if conditions are encountered during take off were thrust is needed the crew should not hesitate to manually advance thrust levers to maximum to thrust."
they have a note:
"NOTE: an increase in elevator column force during rotation and initial climb may be required for ATM takeoffs."

may this mean its not supose to trim for ATM for the event of full thrust is
needed during takeoff?


they also say: the Fixed Derate IS A LIMITATION for takeoff and thrust levers should not be advanced forward unless conditions are encountered were aditional thrust is needed. a thrust increase following an engine failure could result in loss of directional control.

john_tullamarine

they also say

Suggest you run a search on derate .. plenty of threads around.

Concern is that

(a) ATM is just a matter of taking off at less than rated thrust. All data remains OK .. provided that the reduction still gets you off the ground etc. in accordance with all the various rules

(b) derate, functionally, is the same as bolting on a lower max (rated) thrust engine .. and ALL the certification bits and pieces are tied to that lower maximum thrust .. including things like Vmca/Vmcg (hence the reference to directional control). So, depending on the actual engine installation, potentially you could run the throttles up to a thrust setting which could embarrass you at lower weight speed schedules ..