The Coast Dog STC was in direct response to a Transport Canada AD restricting 206s to five occupants. Only one middle row seat is permitted to be installed with anyone in row 3 (and no baggage/cargo in that area), along with any occupants in row 3 being required to demonstrate they can independently open the rear doors with flaps extended on the day of flight. This primarily came about after a recent 206 on floats flipped and passengers drowned.
Prior to issuing the AD some TC reports made specific reference that the FAA and Cessna had 'tried' to solve the problem in the past, but all acceptable options were too expensive to mandate. Put some restrictions on 206s, and the industry found a couple solutions in no time.
I do not think Beavers have had restrictions put on them, but I know some Canadian seaplane operators have gotten STCs for modified rear doors with simpler to use and better located door handles to help improve egress from an inverted Beaver. There have been quite a few drowning deaths in flipped seaplanes, and the issue is one of the bigger concerns of Transport Canada.
Last edited by StudentPilot479; 17th Sep 2021 at 07:02.