ZFW

in fact, yes. Weight is also an option just like if you want red or blue seats. Of course not every weight is an option: there is a range in between you can choose: the lower your requested MZFW, the less you will pay to the producer.Concerning the checks: ever seen a load sheet of a B747? It is CLEARLY printed what your MZFW is. Those papers are checked by autorities before you are allowed to use them (crosscheck with the actual aircraft certificate).So, before the calculation sheets can be used, they have to be approved (and the autorities are not going to allow a higher ZFW than allowed by the certificate).When they are in use: it is practically impossible to load the aircraft more then allowed: it will be clearly seen by the pilot on the documents and he will refuse to take off. And when we change some figures? That's fraud ;)A real-life incident which proves how relative the maxima are (and also indicates what I say is true): a few years ago, there was a singapore airlines flight bound for singapore, departing from brussels (cargo) and the take off roll was largely extended, just a few hundred yards before the end of the runway, the aircraft finally took of. Of course, dispatch was warned immediatly by the captain that something was wrong, as the aircraft didn't go in the air at Vr. The aircraft was placed in a holding in the neighborhood of Brussels while dispatch was running all the documents and calculations again. After a few minutes it was clear what the error was: the aircraft weighted 10 tons more then was declared (10 tons above the certified MZFW, as the aircraft was fully loaded) but did take off, and calculations (based on manuals for higher weight classes) showed the aircraft could continue the trip to singapore, remaining within CG limits and having enough fuel. The aircraft arrived safely in singapore without any further incidents.I think this makes my point well clear: the certified ZFW is just a commercial instrument for the producers: "you want us (the producers) to allow you (the airline) to take more on board? Fine, just pay more and we will increase the certified maximum weight" (Of course keeping in mind that ZFW+Fuel has a direct effect on maximum T/O weight and is therefor also influenced by commercial thinking by the producers)Nick