Every time it is worn!
Every time the PFD is worn
Every time the PFD is worn
Every time the PFD is worn
Every time the PFD is worn
Every time the PFD is worn.
Every time the PFD is worn
Every time the PFD is worn
According to the manufacturers instructions.
Inflatable PFD
Every time the PFD is worn
We do not know what you mean by "PFD", please do not use abbreviations. But the answer would be when the instructions for the "PFD" say it needs to be replaced.
a pfd for everyone aboard