737NG cruise CG

[Sue Ridgepipe]

I'm hoping someone here can help with more info about the cruise cg on the perf init page in the 737-800.
I believe there are a couple of default values used - 26.2% by the FAA and 5% by the CAA.

Why do they use different figures, and does this translate to much of a difference in the max alt?

Also, what do people generally use? Our company uses 26.2% and we never touch it, but are there any companies out there that have their own settings and why?

[plain-plane]

Well FR drivers are not allowed to touch the default of 5%...:confused:
And yes it does make a difference of approx 2000' (if I remember correctly)

Also in EASA country the buffet margin in 1,3 and in the US it is 1,2...:confused:
So we are often flying around 3000 ' lower than our US cousins:cool:

[Checkboard]

I normally enter a value about halfway between the take-off CG and the ZFW CG values on the load sheet. 26% is typical. 5% is the forward limit = highest stalling speed, so the worst case for the buffet limit display.

(Stall speed increases with forward CG, as the tail carries less of the load/provides more down force, which then has to be taken up by the wings, i,e a higher angle of attack for any given weight.)

[speedbird37]

we use MACTOW -4% on the cruise CG

[mrjet]

"Well FR drivers are not allowed to touch the default of 5%...
And yes it does make a difference of approx 2000' (if I remember correctly)

Also in EASA country the buffet margin in 1,3 and in the US it is 1,2...
So we are often flying around 3000 ' lower than our US cousins"

Plain-plane you don't remember correctly. It's a few hundred feet you lose at the most, especially since FR load their aircraft with a forward CG anyways.

The gain in manuever margin far outweights the minor loss in altitude capability by leaving the CG at 5%.

[relax.jet]

We do T/O CG - 4 units

[levantes]

We use 18% CG on the PERF-INIT page for the whole flight which I find the number to be quite realistic.
It makes a huge difference especially when you do a 5-6 hour sector with respect to fuel!

[KristianNorway]

We use the lowest of the stated MAC CG-values on the final loadsheet and subtract 5% for additional safety margin.