COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES SAAB SF340 Series Aeroplanes AD/SF340/57 Amdt 1 Horizontal Stabiliser Front Spar Fastener Holes 1/99 Applicability: Model SF-340A, serial numbers SF-340A-004 through SF-340A-159, and model SAAB 340B, serial numbers 340B-160 through 340B-439. Requirement: Action in accordance with SAAB Aircraft Service Bulletin 340-55-34. Note: LFV AD 1-133 refers. Compliance: As specified in the Requirement Document with a revised effective date of 28 January 1999. This Amendment becomes effective on 28 January 1999. Background: During simulated flight testing in the "Full Scale Fatigue Test Rig", fatigue cracks were found in the forward spar of the horizontal stabiliser. The cracks were located at the intersection between the rear fuselage and the forward spar upper spar cap. The starting point for the initial crack is considered to be in the upper part of the web at one of the fastener holes. Amendment 1 is issued in response to a new Requirement document which introduces a Cold Working Expansion Procedure for four of the holes in the upper cap and the web. This procedure will extend the fatigue life and minimise future need for repairs. The original issue of this Airworthiness Directive became effective on 14 August 1997.