Why does the Mitsubishi MU–2B have its own SFAR?
Since the MU-2 weighs less than 12,500 lb, a type rating is not required to fly the plane, so pilots only need a multi-engine rating. However, it is a high performance pressurized aircraft that requires more skill to fly. Mitsubishi Heavy Industries asked the FAA to create a type rating requirement for the MU-2, but the FAA decided on creating the SFAR instead, which is more strict than a type rating, especially in the amount of training specifically required.

Research showed that the accident rate of the MU-2 from 2001 to 2005 was not really exceptionally high compared to aircraft of similar size and performance. While the accident rate was higher than some, it was also lower than others. However, the FAA received a lot of pressure to create a rule for the MU-2.

Regardless, the accident rate has gone down significantly since the FAA created new regulations for the plane.