B738, EEC altn./assumed temp

[KristianNorway]

Hello gents

Can you guys tell me why it's not possible to use the assumed temperature reduced thrust method with EEC's in alternate mode?

Also, I read that during a takeoff in soft alternate mode the engine may windmill during takeoff, increasing N1 by as much as 7 %. What does the EEC do during normal conditions to stop this from happening?

[de facto]

Can you guys tell me why it's not possible to use the assumed temperature reduced thrust method with EEC's in alternate mode?

Simple, Boeing says NO,not allowed.I guess its because you will use performance restrictions to calculate your vspeeds and you dont have ass temp tables provided for that condition.

Also, I read that during a takeoff in soft alternate mode the engine may windmill during takeoff, increasing N1 by as much as 7 %.

You dont take off using soft alternate mode,you will be using the Hard Alt mode following your DDG.
N1 may increase during roll out but yet again if you follow your DDG, a weight penalty will occur,reducing your N1 for the weight,keeping it below your max thrust rating N1 limit,even with 7 perc roll increase.(26k for actual conditions)

What does the EEC do during normal conditions to stop this from happening?

It uses the great tool of Autothrottle and its computer.

[KristianNorway]

Simple, Boeing says NO,not allowed.I guess its because you will use performance restrictions to calculate your vspeeds and you dont have ass temp tables provided for that condition.

The question still is why. I get the theory behind no ass. temp. with contaminated runway or anti skid inop. Here you have a restriction due to a longer ASD, but I still don't get the EEC in alternate.

You dont take off using soft alternate mode,you will be using the Hard Alt mode following your DDG.
N1 may increase during roll out but yet again if you follow your DDG, a weight penalty will occur,reducing your N1 for the weight,keeping it below your max thrust rating N1 limit,even with 7 perc roll increase.(26k for actual conditions)

Of course you're right regarding hard alternate. I was a bit quick when writing there. Thanks for the workthrough!
Can the reason for the restriction be because of the lower thrust setting in the DDG? If you factor in a roll increase to maintain N1 within engine limits you couldn't count on those extra N1 figures for performance reasons..

[de facto]

Can the reason for the restriction be because of the lower thrust setting in the DDG? If you factor in a roll increase to maintain N1 within engine limits you couldn't count on those extra N1 figures for performance reasons..

No,the restriction is there so the fact of possible n1 increase during roll out does not go beyond the n1 limit for temp and pressure for the engine rating.
To reduce the take off N1 ,your take Off limit weight is restricted by a certain weight value in the AFM DPI section....

but I still don't get the EEC in alternate.

Sometimes ass temp is just not the priority of the day....EEC in alt mode is one.
Sorry,i am not sure but it .could be as simple as boeing can not know the temp the EEC in its reversion mode(alt) and therefore cannot provide assum temp table as climb and runway limit need the info of actual OAT.
Just a guess and stand to be corrected