Re; the MEL (if true). How could that NOT be negligence, in light of what transpired? Lawyerfest......
Provided the MEL has been applied appropriately, then there is no "legal" problem, apart from the manufacturer's and regulator's decision to create such an MEL in the first place.
A jet I have flown had two overspeed protection systems; one electric and one mechanical. Either would shut down the engine if the front end (N1) became disconnected from the back end (N2). The electric overspeed protection system was MEL-able. That may be the situation here.
On my current aircraft, a Cat A MEL has the time or cycle limit stated in the MEL text for the item. A Cat B MEL expires after 3 days, a Cat C MEL after 10 days and a Cat Z MEL expires at the next EBA negotiation finishes.
