COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Enstrom F-28 Series Helicopters AD/ENST 28/34 Main Rotor Shaft 10/93 TX Applicability: Models F-28A, F-28C, F-28C2, F-28F, 280, 280C, 280F, and 280FX equipped with composite-wrapped main rotor shaft, part number 28-13183. Requirement: 1. Inspect the main rotor shaft in accordance with Enstrom Service Directive Bulletin No. 0083, dated 16 July 1993. If the shaft is found with separations in the composite wrappings, corrosion, red-coloured residue or cracks, retire the shaft from service and replace with main rotor shaft part number 28-13140-11 or 28- 13104-1. 2. Retire the main rotor shaft from service and replace with main rotor shaft part number 28-13140-11 or 28-13104-1. Note: FAA Priority Letter AD 93-15-10, issued 3 August 1993, refers. Compliance: 1. Inspect the main rotor shaft before further flight after 6 August 1993. 2. Retire the main rotor shaft not later than 10 hours component time in service after 6 August 1993, but immediately if main rotor vibrations develop which cannot be corrected by normal track and balance procedures, or if the vibrations return soon after correction. Background: This AD is prompted by a report of a large crack in a composite- wrapped main rotor shaft. The crack was immediately below the upper radius and was concealed by the composite wrap. Main rotor track and balance problems that arise suddenly, or those that do not respond to normal corrective actions, could be caused by a cracked shaft. This condition, if not corrected, could result in failure of the shaft, loss of the main rotor, and subsequent loss of control of the helicopter.