How many consecutive fasteners should be installed into a scrap assembly before countersinking holes in the final assembly?

The correct answer is five. In aerospace assembly practices, it is important to consider the structural integrity and the precision required in the assembly process. The guideline to install five consecutive fasteners into a scrap assembly before countersinking holes is established to ensure that enough data is gathered to identify any potential alignment or fitment issues.

This practice helps technicians verify that the fastener installation sequence is correct and that tools are functioning properly before making permanent modifications, such as countersinking. If countersinking were to be done prematurely, any errors detected later could lead to additional rework or substandard assembly, which undermines safety and performance standards in aerospace applications.

In contrast, the other options — two, three, or ten fasteners — do not meet the established standard for ensuring adequate checks and balances to confirm that the assembly process is on track before irreversible steps are taken.