A state audit is questioning Iowa State University's use of donations to buy an airplane used largely by former President Steven Leath to work on his piloting skills.

A report released Tuesday says the school failed to get required written permission from the executive director of the Board of Regents for the $498,000 purchase.

It says Iowa State should consider requesting reimbursement from Leath, now the president of Auburn University, for a March 2016 trip in which he was flown to his North Carolina home.

The report notes that 52 of 76 trips on the aircraft were used for Leath to obtain his instrument rating. Given its limited use for "clear business" reasons, the audit questions whether the purchase served a university purpose.

The university is defending the purchase, saying the plane facilitated Leath's fundraising activities.