Fluid-tight mechanical fastening system and associated structural assembly

A structural assembly comprising:

• a first member comprising an external side and an internal side, said first member defining a first member through-bore;
• a second member comprising an external side and an internal side, said second member defining a second member through-bore aligned with said first member through-bore;
• and
• a mechanical fastening system comprising:
• an outer bushing at least partially received in said first member through-bore proximate said external side of said first member, said outer bushing defining an outer bushing through-bore;
• an inner bushing at least partially received in said first member through-bore proximate said internal side of said first member, said inner bushing defining an inner bushing through-bore and comprising a flange positioned in a gap between said internal side of said first member and said external side of said second member, wherein said flange is in sealing engagement with said external side of said second member;
• a fillet seal sealing an interface between said flange and said internal side of said first member;
• a nut plate in sealing engagement with said internal side of said second member, said nut plate defining an enclosed clearance bore and comprising a nut received in said clearance bore, wherein said enclosed clearance bore extends from a first end portion adjacent to said second member to a second end portion opposite said first end portion, wherein said first end portion is an open end and said second end portion is a closed end;
• and
• a bolt extending through said outer bushing through-bore and said inner bushing through-bore, and into threaded engagement with said nut.

A method for assembling a first member and a second member comprising:

• forming a first member through-bore in said first member and a second member through-bore in said second member;
• inserting a bushing into said first member through-bore, said bushing defining a bushing through-bore and comprising a flange, wherein said flange abuts an internal side of said first member;
• connecting a nut plate to an internal side of said second member, wherein said nut plate defines an enclosed clearance bore aligned with said second member through-bore and comprises a nut received in said clearance bore, wherein said enclosed clearance bore extends from a first end portion adjacent to said second member to a second end portion opposite said first end portion, wherein said first end portion is an open end and said second end portion is a closed end;
• aligning said bushing through-bore with said second member through-bore;
• and
• inserting a bolt through said bushing through-bore and threading said bolt into engagement with said nut.