Raytheon Aircraft Company has succeeded in lowering the per-day operating cost of the King Air B200 aircraft. By making internal airflow changes to improve cooling, Pratt & Whitney Canada has increased the aircraft's Time Between Overhaul (TBO) from 3,000 to 3,600 hours for the PT6A-42 engine. The company is also increasing the engine's Hot Section Inspection from 1,500 hours to 1,800 hours. Existing operators of B200 aircraft with PT6A-41 or -42 engines can have them retrofitted in the field.