Ok... I’m wondering what I’m doing.... so basically...
gross weight 2655kg and 666 index units... main tanks full... aux empty... max fuel that now can be added in the aux tanks.....
So it’s similar to question 3 of ex 5.13?.., but I’m not getting the sums to work.....!

Can you give me the question number and page number please.

Hey Bob... it was question 25 of the practice exam 1...
I’m just confused as in the book, says adding fuel to the aux tanks will move the c of g back.. so why now... when adding fuel to the aux tanks... am I going to the forward limit by adding to the aux tanks?

I agree. there's something wrong there. Looks like it should have said 'how much fuel can now be burnt from the aux tanks. We'll check it out.

OK. I've checked it out. There's nothing wrong with the question, but it is a tricky one.

While it is true that adding fuel to the aux tanks will move the centre of gravity back, the FORWARD LIMIT also goes back as weight increases. It turns out the the forward limit goes back faster than the centre of gravity does.

So adding weight to the aux tanks will eventually put you outside the forward limit even though the centre of gravity is moving back.

The only way to solve the problem is with the 'two point' method because you are adding weight to hit the forward limit.