The report prepared by Rich Delmar, counsel to the Treasury inspector general, said that in many cases Mnuchin's office relied on "a single boilerplate statement" to justify the use of military aircraft rather than the more complete "facts and arguments" that are required.
Mnuchin's office said it would incorporate "enhancements" called for by the report in future travel requests. Mnuchin's requests included one, later withdrawn, for a government plane for use on his European honeymoon.
The IG report on Mnuchin's travels was the latest chapter in a controversy over expensive plane flights taken by top Trump administration officials which has already cost one Cabinet secretary his job. Health and Human Servivces Secretary Tom Price resigned last week after questions were raised about his use of private jets for multiple government trips.
The Treasury report said Mnuchin's staff had made nine requests for the use of government aircraft since Mnuchin became Treasury secretary this year, including a request for a government plane this summer for Mnuchin's honeymoon travels to Britain, France and Italy.
That request was later withdrawn. Mnuchin has said that request was made because of the need to have access to secure communication lines and was withdrawn after alternative ways to provide the secure lines was obtained. One plane request, for a trip in October to the Middle East, has not taken place yet.
The report said that the travel requests had a similar failing in that they did not provide enough detail on why the travel fell within the requirements set down in a 2011 White House memo. "To be considered a White House support mission (and thus qualify for a plane) the president must have specifically directed that the travel occur," the Treasury report said. "Travel that is simply in general furtherance of a presidential initiative does not qualify."
Trump administration officials said last week that they have tightened up on their approval process and the use of government airplanes by Cabinet officials. The Treasury report detailed some of the high costs associated with the use of military aircraft. It said that Mnuchin's trip in March to London, Berlin and a Group of 20 major industrial economies meeting in Baden-Baden, Germany cost $301,167 with a per-hour cost for the airplane put at $15,994.
Mnuchin's travel to a Group of Seven finance ministers' meeting in Bari, Italy, in May cost $314,442, the Treasury report said, while a Mnuchin trip to Ottawa in June to meet with his Canadian counterpart cost $16,350. Mnuchin's wife, Louise Linton, was on that trip and the report said that Mnuchin had reimbursed the government for the cost of her travel although it did not provide details of the amount of the reimbursement.
Mnuchin also reimbursed the government for the costs of his wife's travel with him to Louisville and Fort Knox, Kentucky, in August. That reimbursement was not broken out but the total cost of the flight was put at $26,900. While Mnuchin viewed the total solar eclipse that day with Sen. Mitch McConnell during the trip, the Treasury report said that "there is no indication that the date was chosen to coincide with the solar eclipse."
The trip had initially been scheduled to occur earlier in August and had been pushed back to accommodate a delay in the Senate's August recess, the report said. The Kentucky trip attracted attention because Mnuchin's wife posted a photo on Instagram of the couple stepping off the government jet. In her post, Linton included hash tags of various luxury designers she was wearing.
That prompted criticism from an Oregon mother who wrote "glad we could pay for your little getaway." Linton fired back that she was "pretty sure" she and Mnuchin had paid more in taxes than the Oregon woman had to cover the trip. Linton later apologized for her comments.