A local canine rescue non-profit is looking for pilots to transport animals to new homes and offering to reimburse for fuel and possibly operating expenses. Part 91 has exemption criteria for sharing expenses on passenger-carrying flights, but what about carrying animals? Can the pilot legally be reimbursed? Would the answer to this also apply to transport of blood?
Not legal to accept money in any amount for either dogs or blood without a Part 135 operating certificate. And the only one breaking the law for that would be the pilot, so you can't stop the rescue group from making an offer which isn't legal for the pilot to accept. But it might be a good idea to let them know they're inviting unsuspecting pilots to break the rules.
Sharing expenses under Part 91 requires that you have passengers, not cargo. You have to avoid “holding out” to the public. You have to have a “common purpose”. You can only share direct expenses such as fuel, oil, landing fees, etc. You have to share on a pro-rata basis based on the number of people in the aircraft. Part 91.146 and 91.147 offer some exceptions for receiving compensation for charitable flying and aerial sightseeing but both involve passengers, not cargo, and 91.147 requires a letter of authorization among other things.
If you are a Commercial Pilot, you can receive compensation under various types of operations listed in 119.1 without an operator certificate when common carriage is not involved. Transporting cargo is not included except for emergency mail service in case of a disaster.