The state of Missouri's fleet of 19 aircraft hasn't been used to its full capacity, Auditor Tom Schweich has determined.

The aircraft of six fixed-wing plans and helicopters operated by the Highway Patrol and departments of Conservation and Transportation costs $3.3 million a year to operate. In addition, the state employs 16 pilots at a cost of $1.5 million.

"The state airplane fleet is larger the necessary, there is duplication of efforts between agencies, and, despite the low utilization of state aircraft, state agencies incur unnecessary costs for chartered flights," Schweich said in a release.

The crux of Schweich's criticism focuses on duplication of flight services by the three agencies that's causing increased costs for the pilots and chartered flights. For the two year period analyzed (ending June 30, 2013), the state paid $183,000 for chartered flights even though state-owned pressurized passenger planes were available on 67 percent of the days of the charter flights, which resulted in $122,000 in unneccesary costs.

The state's Department of Transportation allowed non-authorized pasengers on state passenger flights, including spouses, family members and former commissioners in violation of state policy, the audit found.

The audit also found fault with the billing rate calculation used by the Missouri State Highway Patrol, because it didn't include operating costs such as mechanic fringe benefits, pilot training, hanger expense, other clerical and administrative expenses, and amortization of the purchase price of the aircraft. The error caused the agency to miss out on $191,500 from state agencies.

View the full audit report here.