The prime consideration remains accuracy and repeatability - which are usually expressed in terms of full scale reading.
Typical commercial weighing systems might be in the order of 5%.
A serious aircraft weighing application looks to much tighter limits .. Australia, for instance, requires 0.2% ... never mind that the majority of weighing kits can't really make that limit anyway.
Aircraft weighing kits are dramatically more expensive than their commercial cousins because of this sort of requirement ... and the errors in weighing aircraft and traps for young players .. let's not go there ... another hobby horse of mine.
On board systems are affected by a variety of error-inducing boundary conditions and, at best, are a useful guide only. I have never seen an on board system agree with the load sheet data but one should see a sensibly, if approximately, constant error. The secret is to watch for a divergence in error which is cause for investigation.
Keep in mind that we are not all that worried about very minor errors.
The value of such systems lies in picking up those errors which come out of left field and bedevil the safeguards built into traditional weight and load control systems used by airline and other operators.
Things like
(a) a defective weighbridge causing all the can weights to be straight out of fairyland .. I recall one such event where the bridge picked up some FOD which affected the system articulation .. picked up by a freighter crew which queried a sudden change in the on board system error history.
(b) cans loaded in the incorrect order .. shouldn't happen but does so far too easily at oh-dark-thirty in the rain. Good reason for the flight crew to do a followup check in those aircraft which have access post loading .. does your loading protocol have an independent person ticking off the cans as they go into the hole ?
(c) cans intended for one aircraft ending up in another .. likewise
(d) significant fuel misloads ... the Gimli glider was only one of many which has been caught by this gremlin.
I'm sure that others can add to this list ....
Last edited by john_tullamarine; 17th Nov 2004 at 21:02.