True, though this may mean many things. The only part of CFR 14 that mentions that a certificate is required for operating aircraft is CFR 14 61.3 which states that an unexpired certificate is required to `exercise the privileges' of that certificate. So if the PAO does not require the certificate to begin with, this part does not apply and one only has to comply with part 91 rules. Again, feel free to disagree, the sheriff told me this so who knows:)