Working on the ADAHRS bracket. This bracket is an add on sold by Vans to install the ADAHRS module of and EFIS system. The bracket is placed at bulkhead F707 and connects with F787 stiffener web and the top fuselage J stiffeners

First deburred and sanded the bracket itself. It looks kind of funky and has a lot of predrilled holes for all kind of brands of ADAHRS modules from different EFIS suppliers.

Next I drilled the bracket in place. Being level is key here as the ADAHRS will define your horizon position in the EFIS screens.

I used a digital level clamped to the bracket to ensure 0.0 position.

All drilled to #30 for LP4-3 pop rivets.

 After drilling, still all perfectly level.

Also in the longitudinal direction. It's best to do this drilling while the fuselage is fully level on the longerons. Once the fuselage is on it's landing gear, it's very difficult to get this right.