What is done in an acceptance flight?
I suppose it also depends on the situation. Are we talking about an acceptance flight from the factory, heavy maintenance test, or something like a lease return/sub-lease acceptance flight?
We had some pretty bad experiences following subcontracted heavy maint work (B744's)and developed our own flight test program for this purpose. Basically it was a factory acceptance test with some of our own stuff throw in and took 2 full days although the flying portion only took about 5 hrs. One thing you should keep in mind is are the crew qualified for that type of flying. Depressurizing, overspeed warning tests, IFSDs, etc are not for regular line guys. (One of 744's was at M.94 I believe when it was agreed the ovrspd warning wasn't working.) The insurance companies will raise caine if they find out. If you put the question to Airbus they'll agree. (Of course they'll offer to do it for you at a price you wouldn't believe.)
For a lease return or sublease acceptance flight read the contract first especially if your the lessor. These I find very interesting. Keep in mind that it's an in service aircraft with well maintained logs and a maint history that their inspectors have poured over for 5-6 weeks. A simple 1 hr flight to show it's fully functional should suffice. I've seen airlines request the full up factory test but the leasing return conditions usually specified much much less. The clincher when the shouting starts is "well if that's what the lawyers wanted then thats what they would have stated that explicitly in the contract just like they did with everything else." In the end we usually do a few extra tests just to smooth things over but it's a long long way from an factory acceptance test.