Friedman (P), a commercial airline pilot, has been diagnosed with Insulin-Treated Diabetes Mellitus (ITDM), and although he holds a third class medical certificate authorizing him to pilot non-commercial flights in the United States, he seeks the first class certificate necessary to serve as a commercial airline pilot. Congress has granted D broad authority to regulate those 'practices, methods, and procedures the Administrator finds necessary for safety in air commerce and national security.' D has established rules requiring pilots to hold both a medical certificate and a pilot certificate. D lists a number of conditions generally disqualifying for any class of medical certification, among them a 'medical history or clinical diagnosis of diabetes mellitus that requires insulin or any other hypoglycemic drug for control,' otherwise known as ITDM. D has the discretionary authority to grant exceptions to the medical regulations. Regulations require the Federal Air Surgeon (FAS) to make his determination using standards published for each condition as set forth in the FAA's Guide to Aviation Medical Examiners (AME Guide). Regulations require the Federal Air Surgeon (FAS) to make his determination using standards published for each condition as set forth in the FAA's Guide to Aviation Medical Examiners (AME Guide). The process includes a medical examination performed by a member of the community of Aviation Medical Examiners (AMEs), and it may require pilots to provide additional medical information to the FAA where necessary. In 1996 D reversed its ban on those with ITDM and allowed a third class medical certificate (but not a first-class certificate). Based on actual results from third class pilots, D amended its AME Guide to broaden the third class ITDM protocol to all classes of medical certificates on April 21, 2015. P submitted a completed application for a first-class license to the FAA. D requested supplemental information. D was looking for continuous glucose monitor readings. P responded that he did not use a continuous glucose monitor. CGM uses a sensor inserted under the skin to check glucose levels in tissue fluid. A transmitter sends information about glucose levels via radio waves from the sensor to a wireless monitor. CGM data is not as accurate as other blood glucose measures like fingersticks. CGM is costly and is not covered by insurance unless medically necessary. Two days after Friedman wrote to D to note the Agency had requested information beyond its own published evaluation protocol, D revised its AME Guide. Under the new guidelines, P's application would be denied if he did not indicate he planned to comply with 90 days GCM data. P again advised D he did not possess any CGM data. P also presented letters from his physicians explaining CGM was not medically necessary in his case. The Expert Panel even submitted a letter in support of P's application. P eventually wrote D and explained he had to submit the data or he would not be approved. P claims D has behaved in an arbitrary and capricious manner in assessing his request for a commercial airline pilot's license.