After a year-long safety review, the Federal Aviation Administration (FAA) issued a Special Federal Aviation Regulation (SFAR) calling for increased pilot training, experience and operating requirements for the Mitsubishi MU2B aircraft, saying the aircraft was more complex that other light twins and turbines in its class. The SFAR, estimated to cost $40.6 million and bring $85.4 million in benefits, would be effective 180 days after the final rule.

The aircraft, certificated in 1965, has moved from corporate and business aviation to personal use and air taxi operations, especially cargo hauling. Of the 397 aircraft on the U.S. registry, the majority are operated under Part 91 as personal-use aircraft. As of April 2006, 64 MU2Bs were being flown by 18 different Part 135 operators in the U.S. FAA blamed the shift for an increasing number of accidents, a total of 12 between 2004 and 2005 with 14 fatalities.

The FAA evaluated training programs for the aircraft and, concluding they were inadequate, directed Mitsubishi to develop a new training program, which has since been certified. The SFAR requires all pilots to undergo the new training program as well as annual recurrent training. It also established a minimum standard of 100 hours of pilot in command on multi-engined aircraft for pilots to operate the aircraft. (Docket #FAA-2006-24981)