those for similar turboprop aircraft. Additionally, although some owners had worried that the SFAR would depress aircraft prices even further, resale values rebounded as potential owners recognized that the aircraft is very safe with a properly trained pilot. PROP seminars continue to be held biennially and count towards MU-2 training requirements, and have become popular social events for MU-2 operators and even potential buyers, as MU-2 ownership is not required for attendance. The aircraft had several airworthiness issues early in its service history. Airworthiness directives (ADs) were issued for nose gear cracks and various problems with the TPE331 engine. In April 1993, an emergency AD was issued after four serious accidents, two of them fatal, caused by propeller blade separations in aircraft equipped with similar three and four-blade Hartzell propellers; the AD required immediate inspections of the propeller assemblies having more than 3,000 flight hours, and also covered various other aircraft types, but focused on the MU-2B-60 since it was the heaviest aircraft using these propellers. Despite these early problems, aviation experts have characterized the MU-2 as being robustly designed and constructed, and relatively few MU-2 crashes have been directly attributed to mechanical or structural failures. Variants Short fuselage XMU-2 Astazou-powered prototype, one built MU-2A Astazou-powered development aircraft, three built. MU-2B Production variant with Garrett TPE331 engines, 34 built. MU-2C (MU-2B-10) Unpressurized variant for the Japan Ground Self-Defense Force, four built. MU-2D (MU-2B-10) Improved MU-2B, higher operating altitude and bladder fuel tanks rather than wet-wings, 18 built. MU-2DP (MU-2B-15) MU-2D with 90-gallon tip tanks and upgraded engines, three built. MU-2E Unpressurized variant for the Japanese military designated MU-2S MU-2F (MU-2B-20) Variant with improved engines and 90-gallon tip tanks as MU-2DP but certified at a higher gross weight and additional fuel tanks, 95 built. MU-2K (MU-2B-25) Short fuselage variant of the MU-2J, 83 built. MU-2M (MU-2B-26) Revised variant of the MU-2K with increased weight, and increased cabin pressure, 27 built. MU-2P (MU-2B-26A) Improved variant with four-bladed propellers and improvements as MU-2N, 31 built. Solitaire (MU-2B-40) Variant with improved engines and increased fuel capacity, 57 built between 1979 and 1985. Long fuselage MU-2G (MU-2B-30) Stretched variant with a 1.91m increase in length, larger cabin and change to landing gear configuration, first flown in January 1969, 46 built. MU-2J (MU-2B-35) Variant with improved engines, eleven inch increase in cabin length and increased gross weight, 108 built. Revised variant of the MU-2L with increased