Looks like Dimples......

[chperplt]

Landing in LGA yesterday, I noticed a NW 757 that looked like it had dimples on its belly, aft of the wing, but forward of the tail. I then saw a US 737 that had the same thing in about the same place. It looked like a flat golf ball. I assume it was a repair of sorts.

Anyone have any ideas???

 

[flywithastick]

I'm guessing (maybe even wildly) that it's just where the skin is sucking in where riveted to the internals. Depending on the loading at the time, quality of fit, pressure differentials, etc. you can see some deformation at the rivets that might look like dimpling. The upper surface of my RV wing looks kind of dimpled when in flight with the low pressure tending to lift the skin between the ribs/rivets.

This sound like what you're seeing?