Weight and Balance system

[747FOCAL]

Can somebody explain the positives (and negatives) of having an onboard Weight and Balance system that feeds info to the FMS when the aircraft is on the ground?

Thanks :)

[jettison valve]

747FOCAL,

I am no W&B pro, not at all. But here is what I am thinking of:

Positive:
- It may avoid typos (so far, the driver has to enter f. e. ZFW and ZFWG to initialize the FMS), which can result in faults ("excess aft cg" warning) and subsequent manual fuel xfers during flight.
- It *may* serve as a cross check for the traditional way of W&B. Apparently, AI tested a system on A320s which was found to be very accurate. On the other hand, some B747F operators deactivated such a system due to the poor reliability.

Negative:
- Poor reliability (see above),
- Doesn´t take running loads (f. e. lbs/in) into account; therefore, the load sheet has to be done anyway!

Waiting to see the experts´ answers,
J.V.

[john_tullamarine]

Precisely for the same reason such systems have been saving flightcrew's necks for the past 30-40 years .. they provide an independent gross check on

(a) loadsheet mistakes due to finger trouble

(b) loadsheet mistakes due to weighbridge defects .. very important for freighters where it is super easy to end up with a very, very large incorrectly reported can weight (OK, mass ..)

(c) physical loading errors .. the next time a can load is put in back to front, or the cans get mixed up ...won't be the first .. or last ...

I have experience on two systems in years gone by .. neither was terribly accurate but the error was reasonably consistent so the gross check need worked fine ... one just kept the zero error in mind when comparing apples with oranges ... saved my neck once or twice along the way.