The U.S. Air Force Academy, at Colorado Springs, Colo., has grounded 45 of its aircraft due to safety concerns after inspectors discovered "maintenance irregularities," the Air Force said on Tuesday. The fleet is maintained by a contractor, Doss Aviation, and will remain grounded while Air Force officials review and investigate discrepancies. The grounding affects UV-18s, gliders, motorgliders, T-41s and Cessna 150s. Safety concerns arose following the Jan. 2 engine failure of a UV-18 Twin Otter that was en route to Florida to pick up cadets from a parachuting competition. The Twin Otter had no passengers on board, and landed safely at Tinker Air Force Base, Okla. The news release said academy officials will keep affected aircraft on the ground until confidence is restored in the safety of the maintenance program and permanent fixes are in place for all discrepancies identified. Aircraft maintained by Embry-Riddle Aeronautical University and used for introductory flight training by ERAU instructors, is not affected. The contractor has directed an immediate independent audit of company operations at the academy. Company auditors will look at maintenance and management practices. Academy officials will work closely with the auditors and provide oversight and assistance, according to an academy news release.