AIX uses XCOFF that has diverged from COFF so much that it is easier to treat it an entirely separate lineage – not entirely different from the Windows' PE object/executable format, which is also a COFF derivative.

XCOFF is pretty cool, actually, e.g. it does not require for two sets of the same library to exist, i.e. one to use for static linking and another for dynamic loading – the same .a archive can be used for both.

The .loader section keeps import and export symbol tables (what the binary provides to others, and what it needs resolved), library search paths and dependencies, and relocation and fix-up details. If the .a is being used for static linking, the .loader section is simply ignored.