A mystery???

Or perhaps not.

If it was a serious structural issue, don’t you think Boeing would have it hidden away in a hangar with its engineers crawling all over it?
They certainly wouldn’t leave it out in the open for all to see.

Assuming of course there is room in the hangars now, given all the other fault testing going on! :diablo: 😉

Or perhaps not.
That is the leading edge of the tail which is not a structural component, just an aerodynamic one.
What we see here is an early section 47 barrel (we know its early as it has 5 windows. The 5th was deleted from the design after the early test barrels).
The absence of Section 48 (the section the tail attaches to) means this cannot be a structural test.

It is most likely some continuing electrical discharge testing or possible some sort of test for the leading edge’s de-icing properties.

If it was a serious structural issue, don’t you think Boeing would have it hidden away in a hangar with its engineers crawling all over it?
They certainly wouldn’t leave it out in the open for all to see.

Well presumably they’ve realised they now have a structural fault where the vertical stabilizer joins the fuselage…..that’ll be the next revamp and delay!