Hudson Waterbus
Frequent SLF here, with a few comments in response to several earlier posts.
I recall from a few years ago travelling on some US domestic flights where the safety card said that the seat cushions were the only personal flotation devices, and that they were designed with straps through which one should insert ones arms. Perhaps USAir takes this approach.
I am fairly sure that BA safety cards, on some types at least, warn against attempting to open doors that are not clear of the water.
From fairly recent experience of ferry trips round New York and Victoria, Canada, and watching float planes taking off and landing in Victoria, it seems probable that water conditions on the Hudson would have been well withing limits for float plane operation. Perhaps this was a positive factor in the USAir success.
Is sea state taken into account designing (land) aircraft hulls for ditching survivability? If so, what limits are used?