curved line above airplane doors

[Taliesin]

The rain gutter alignment has nothing to do with air flow, only water flow.

I think you are wrong there. If you look at the rain gutters you find that they are angled slightly upwards on the first door, more angled upwards before the wing, as air flow upwards, and angled downwards after the wing as air flows downwards. If it had nothing to do with airflow, the angle would be the same on every door but it isnt.