Our PI Manual includes the following section:
"Who May Serve as a Principal Investigator:  Any Colorado State University
non-temporary, salaried state classified or general faculty employee
(including faculty on transitional appointment) may serve as a principal
investigator.  Individuals with other types of appointments (e.g., temporary
and/or non-salaried) require approvals in each instance from their
departments, colleges, the Provost, and the Vice President for Research and
then should be listed as co-principal investigator with a non-temporary,
salaried employee.  Graduate research assistants and post-doctorals are
considered temporary, non-faculty appointments. Faculty affiliates are
non-salaried appointments."

Based on this,  it would depend on the type of contractual arrangements the
department had struck with the faculty member.  If totally retired, then a)
approvals definitely needed and b) co-PI probably needed (although Emeriti
faculty have an established track-record, so the co-PI might be deferred)

................................................................
Celia S. Walker
xxxxxx@vines.colostate.edu
Colorado State University