This matter has been discussed under earlier topics about Impulse.
Impulse elected to go for the 110,000 lbs certification as it suited the MEL - SYD - BNE stage lengths and saved then money in charges. However you then strike problems in operating over shorter stage lenths ie MEL _ LAU, MEL - HBA, hence mlw probs have arisen. They will obviously have the aircraft re certified to higher weights to overcome the problem and pay proportionaly more in weight based charges.
The DC9 - 30f's were at a far higher weight than the DC9 - 30's used in pax service by TN and AN.
The DC9 - 30's used by TN and AN were seated for 91/94 seats and not 117 seats which is the QF B717 configeration.