I have a question regarding Visual COBOL support under AIX.
Does Visual COBOL run under IBM AIX 5.3?
Visual COBOL was not tested under AIX 5.3. It was tested and certified only under AIX 6.1 and AIX 7.1. It may work anyway, but the chances are not good.
Here is a Knowledgebase article describing the file $COBDIR/docs/env.txt, and the general subject of supported versus unsupported OS versions: