The Series 400 will be appended to the existing type certificate for the preceding versions (1, 100, 110, 200, 210, 300, 310, 320) of DHC-6 aircraft.
Certification is not my speciality, but to the best of my knowledge, the 400 follows substantially the same cert basis as the 300, except in areas where the aircraft has been modified (for example, the new avionics), in which case the prevailing (most current) certification criteria is applied.
There are some areas in which Viking has voluntarily upgraded the aircraft to a more contemporary cert basis that what is required.
Hope this provides more clarity than confusion...
