@Avionimc: I took a look at the link you posted and dug further...and this is what I found.
It doesn't say what you stated, actually. It says that it's based on the certificate basically, when speaking about an ATP. I quote below:
§61.23 Medical certificates: Requirement and duration.
(1) Must hold a first-class medical certificate:
(i) When exercising the pilot-in-command privileges of an airline transport pilot certificate;.....
So stopped there. Doesn't say anything about Part 91...however does mention 121 ops.
So now I am thoroughly confused. My company is telling me it's only required every 12 months for flying the private owner around (part 91) but does it not require me (to be PIC) utilize my ATP to fly the GV type as PIC. I guess more digging required....
Anyone else can shed light on this??
eCFR ? Code of Federal Regulations