You might have a contact point problem.
Compare this aircraft cfg to the default 747 and look at the contact points you might be able to use the contactpoints of the default 747 for the mel jet.just edit out the oldones and replace with copies of the default 747.
Even this might not be enough as there might be a size differance and the refferance points might not be the same. But you might get lucky & it will tkake care of it. 8)