Add seam to centre fuselage inner side skin

I note that the front inner side skin is about 3mm displaced from the natural plane formed by the uprights. The centre fuselage inner skin would have to flex to lie flat against this skin. As supplied, the holes in any case do not match up so well, with about a 1.5mm mismatch. If the centre fuselage skin is flexed so that the holes match up, and also lies against the front skin, just aft of this is a bowing outwards with significant oil canning.

Both problems are solved by inserting a step. All of this is hidden behind the upholstery.

The approx 5mm high step so formed - while lifting the centre fuselage inner side skin away from the uprights a bit - does not affect the layup of the upholstery.

No disturbance to lay of upholstery