If it was a 747-400 , max Landing weight allowed is 285.800 KG, otherwise it's an overweight landing
Yep, that was certainly the number for ours.....As I recall it ballpark figures figures were if you were up to max ZFW you'd generally need to dump down to around 40 tonnes in tanks before you were at Max Ldg Wt ( structural).
Tanks fuel for the flight in question at departure may have been in the vicinity of 70, plus/minus tonnes, they may well have burnt 10 tonnes climbing out and during the short cruise, so maybe 60 tonnes left in tanks when it went pear shaped with the drunk......so at the risk of speculating ( but isn't that what we are here for) I'd have thought they would have needed to dump around 20 tonnes, maybe less if the ZFW was below max.
TBH can't remember the 744 dump rate...