I gather you're the CFO's boss. None of that is the FAA's concern. That's only the IRS's concern, not the FAA's. However, there is no IRS-approved mileage rate for using private aircraft on business. The rate to which you refer only applies to reimbursement of government employees or contractors by the Federal government. The IRS allows only actual cost, which may be higher or lower than that ratem and requires documentation of that cost. If you take others in the plane with you, you cannot accept any reimbursement from your employer at all. See the Mangiamele interpretation. As a lawyer, you must be aware the US Court of Appeals has held that the NTSB and courts are required to defer to the FAA's interpretations of its own regulations unless that interpretation is "arbitrary, capricious, or otherwise not according to law." See Administrator v. Merrell and NTSB, 190 F.3d 571 (D.C. Cir. 1999). So far, the US Court of Appeals has not found the Mangiamele interpretation or its derivatives to be "arbitrary, capricious, or otherwise not according to law," but since you are a lawyer, you are indeed welcome to try, and I wish you good luck, because I, too, think it's a bad interpretation. However, until that happens, the Mangiamele interpretation has force of law, and your pilot certificate is at risk if you accept reimbursement in violation of 61.113 as the FAA Chief Counsel has interpreted that regulation in that letter. Good luck. There are a lot of folks who feel it's a bad interpretation, but until you manage to get it overturned by the US Court of Appeals, your ticket is at risk if the FAA finds out you're receiving reimbursement for business flights with others aboard. Again, good luck. However, in my opinion, for you to offer legal advice as an attorney that it's OK for a client of yours to violate the reimbursement restrictions in the Mangiamele interpretation would constitute legal malpractice. Anyone who accepts reimbursement in such circumstances is betting that the US Court of Appeals will overturn the Mangiamele interpretation, and that Court rarely overturns the FAA's interpretations of its own rules.