After inspecting the Hi-Lok installation, what should be done if the collar is found to be under driven?

When a Hi-Lok installation is inspected and the collar is found to be under driven, it indicates that the collar has not been adequately tightened to the specified torque or the correct degree of deformation has not been achieved. The integrity of the connection could be compromised, which may affect load distribution and structural integrity.

Re-tightening the collar is appropriate because it allows for the necessary adjustments to be made to ensure the collar meets the installation specifications. Proper retightening can bring the collar to the correct torque, ensuring that the fastener functions as intended and maintains the strength and reliability required in aerospace applications. This process ensures that the fastened joint can withstand the operational stresses it may face during use.

Other options like replacing the collar or discarding it could lead to unnecessary material waste and increased operational costs if the collar can simply be adjusted to meet specifications. Leaving the collar as is would not resolve the issue of it being under driven and could ultimately lead to failure or safety concerns. Thus, re-tightening is the most effective and appropriate action in this scenario.