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 28/2 Amdt 2 Stabilizer Spar Attachment 5/88 DM Applicability: All models F28, F28A, F28C and F28C-2 helicopters, and all model F28F up to and including S/N 743. Requirement: 1. Check the security of the attachment of both left and right stabilizers as detailed in section 5.1 of Enstrom Helicopter Corporation Service Directive Bulletin (SDB) 0076 of 15 December 1987. 2. Inspect and measure the stabilizer spars and attachments as detailed in section 5.2 of SDB 0076. 3. Remove from service any stabilizer spar having a nominal wall thickness of .035 inch. Compliance: For para 1 of the Requirement: Before each flight. Note: This inspection may be performed by the pilot in command in which case certification is not required. For para 2 of the Requirement: (a) if never previously inspected in accordance with previous issues of this Directive; within the next 10 hours time in service after 22 January 1988. (b) If previously inspected in accordance with previous issues of this Directive; within 50 hours time in service after the last such inspection or within 10 hours time in service after 22 January 1988, whichever is the later. (c) Thereafter, repeat the inspections at intervals not exceeding 100 hours component time in service. For para 3 of the Requirement: Prior to further flight after detection. Background: These Requirements follow the November 1987 in-flight failure (overseas) of a spar with .049 inch wall thickness. Amendment 1 which was issued by telex, extended the inspection to additional helicopter models and made the inspection more explicit and more intensive, and effectively placed a 500 hour life on the .039 inch wall thickness spars. Further review has shown this to be unconservative, this amendment therefore requires the thin wall spars, once identified, to be removed before further flight in accordance with SDB 0076.