Federal officials are investigating the state of Michigan's practice of letting its passenger planes be used by officials at Michigan State University for athletic recruiting trips.
The Federal Aviation Administration inquiry comes less than a month after it published a series on the taxpayer-funded planes that focused on how the aircraft are used and who uses them.
The FAA, the Michigan Department of Transportation and the school say a preliminary investigation is underway. MDOT and Michigan State University say the review relates to the East Lansing school's use of the state-owned planes by top athletic officials.
The review could trigger a formal FAA investigation.
MDOT spokesman Jeff Cranson said the FAA is seeking financial documents such as billing, invoices and proof of payments.