411A pay particular attention to the wings;they are of an unusual construction,basically made out milled aluminium planks which have a habit of corroding,very expensive to replace (the wings strength is in the planks) Your surveyor should particularly watch out for corrosion here,it can be very subtle. Worked for Air Contractors who used to operate the beast,good a/c but as has allready been said you must have top notch engineers & a generous maintenance budget (whatever your budget was ,double it,trust me!)