Transportation Secretary Pete Buttigieg and his staff spent nearly $59,000 traveling to official events on government-managed executive aircraft between August 2021 and June 2023, according to an inspector general audit released Wednesday.

Buttigieg opted to travel on the government fleet across eight trips and more than 20 flights, the Department of Transportation's (DOT) Office of Inspector General (OIG) determined in its months-long investigation. Though DOT has repeatedly explained that Buttigieg's use of the jets saved taxpayers money, the audit revealed that just three of the trips were justified by "cost effectiveness," while the others were justified by security, scheduling and communications concerns.

"Ensuring that Federal officials, including career personnel and political appointees, adhere to Federal requirements regarding the proper use of public resources is essential to maintaining public trust and confidence," the DOT OIG report concludes.

"The Department has internal controls over the process to authorize and approve travel on official use of DOT aircraft, such as requiring legal review and approval of all aircraft use justifications, and has implemented new ones, such as expanded voucher audit criteria, to help ensure process standardization," it continues. "Continued oversight in this area is important to maintain transparency and accountability for Federal funds."

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Overall, in the time period analyzed, Buttigieg's flights cost taxpayers an estimated $58,882. The transportation secretary used the jets, managed by the Federal Aviation Administration, to traverse the country, often traveling to local events where he delivered remarks awarding federal funding and grants for local infrastructure projects.

For example, in August 2022, Buttigieg and his staff traveled to Florida, Oklahoma, Minnesota, Ohio, Nevada and New Hampshire, most of which are considered "swing states" during federal elections, on the so-called Building a Better America Tour where he unveiled grants earmarked under President Biden's 2021 Infrastructure Investment and Jobs Act. 

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Buttigieg's use of the FAA aircraft for that trip cost taxpayers an estimated $14,940 and was justified by "exceptional scheduling" needs. 

In another example of his use of the FAA's jets, he and his staff spent $1,822 in April 2022 to travel to New York City for a radio interview and two meetings before returning hours later. Scheduling considerations were again used to justify the travel arrangements.

And Buttigieg most recently used the executive fleet to travel to Mexico for a meeting with the nation's president. That trip cost $14,029 and was justified by "exceptional scheduling; communications or security needs," according to the OIG report.

The OIG noted that, based on DOT's internal calculations, the three trips justified by cost-effectiveness saved a total of $10,678. However, the inspector general found that the agency is not required to "provide documentation to support commercial flight costs or availability information used in cost comparisons," meaning it is impossible to prove those cost savings.

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"As the report confirms, the Secretary travels by commercial airline the vast majority of the time and has directed that travel and logistical decisions be grounded in efficient and responsible use of taxpayer dollars," a DOT spokesperson told Fox News Digital in a statement. 

"The exceptions have been when the Department’s career ethics officials, who have served under both Democratic and Republican administrations, determined that the use of a 9-seat FAA aircraft would be either more cost-effective or should be approved for exceptional scheduling or security reasons," they added. "The majority of times the FAA aircraft was used actually saved taxpayers money, including in instances that were required for exceptional scheduling needs."

The report found that Buttigieg opted to travel on commercial aircraft for 57 trips, or for 82.6% of his total trips. By comparison, former Transportation Secretary Elaine Chao, Buttigieg's predecessor, opted for commercial on 90% of her trips. One of Chao's trips, though, a trip to France in 2017, cost taxpayers a staggering $69,952, the audit showed.

Also, in addition to determining the costs of Buttigieg's travel, the DOT OIG found that the agency, under both Buttigieg and Chao, complied with federal regulations, policies and procedures for the two secretaries' travel on the FAA fleet. But it also noted the agency has used incorrect cost estimates when determining the cost of traveling on the jets, an error that did not negatively impact cost-effectiveness.

"In this holiday news dump, the Inspector General admits that the Department of Transportation has been using incorrect flight cost estimates to justify Secretary Buttigieg’s use of a taxpayer-funded private jet," Caitlin Sutherland, the executive director of Americans for Public Trust (APT), told Fox News Digital. "After stonewalling the release of records for over a year, the Biden administration will try to say Buttigieg is in the clear, but Americans will see through this thinly-veiled attempt to exonerate the Secretary.

"Travelers are spending their hard-earned money and countless hours on flights to see loved ones this holiday season," she continued. "As they sit on the tarmac, they’ll have plenty of time to wonder why they’re paying for their own commercial flights and Buttigieg’s private flights, too."

The OIG audit was initiated in late February after Fox News Digital revealed Buttigieg's use of the jets, citing information obtained by Americans for Public Trust, a conservative-leaning watchdog group, in December 2022. 

Following the Fox News Digital report, Sen. Marco Rubio, R-Fla., sent a letter to the OIG requesting the investigation.

"It is unclear why Secretary Buttigieg would require such costly travel in these instances when more economical options were reportedly available," the Republican lawmaker wrote at the time.