*binary-file-types* contains a list of strings naming file types which
require recognize as binary (FASL) files. FASL files are the output of compile-file, dump-forms-to-file or with-output-to-fasl-file.
You need to add a type to this list if you want load such files but they have an extension which is different from the default (the value of *binary-file-type*).
LispWorks User Guide and Reference Manual - 20 Sep 2017