Originally Posted by
10secondsurvey
I wonder if they'll touch on something which stopped for many years and has returned over recent years. This is the placing of rows of seats at overwing emergency exits.
I don't know what you mean by "stopped"? I don't think there was ever a time when seats were removed altogether from around overwing exits as a matter of generality. Quite a bit of work was done, though, to see what the spacing should be between seat rows was at the exits. IIRC, one of the results was that making the gap too wide actually slows down the flow of passengers; there is definitely an optimum between too wide and too narrow.
There was, though, a specific issue with the 747 Classic. Some operators blocked off doors 3 (overwing) on the main deck, and installed seating all the way from doors 2 to doors 4 (except for galleys and toilets etc, of course). This was because the original certification testing showed that the aircraft could be evacuated well within the required time using all doors, and modelling showed that the certification test could still be met even if doors 3were not used. Consequently, doors 3 could be permanently blocked and the aircraft would still satisfy the certification requirements.
The operators who did this did not do it with the 747-400. There was also a change in the certification requirements, but I don't know which came first. The change was that there is now a maximum permitted distance between two adjacent emergency exits, which prevents the existence of a long gap such as would occur between doors 2 and doors 4 on the 747 main deck. (However, the Classic arrangement was grandfathered.) IIRC, when the A340-600 was under development, Airbus asked for an exemption from this requirement to avoid having to put in another pair of exits (overwing, I think); they could demonstrate that the evacuation test could be completed without those exits. But the request was turned down, I suspect for the same reasons that the requirement was originally inserted, so those exits are now there.