COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Cessna 400 Series Aeroplanes AD/CESSNA 400/88 Horizontal Stabiliser Front Spar Attachment Bolt Retaining Nuts 2/86 TX Applicability: Model 425 with S/Nos 425-0002 to 425-0236 and Model 441 with S/Nos 441-0001 to 441-0354. Requirement: 1. Visually inspect horizontal stabilizer front spar attachment bolt retaining nuts (P/N NAS 1291-8) for cracking. 2. Replace left and right horizontal stabilizer attachment bolt retaining nuts (P/N NAS 1291-8) in accordance with the instructions contained in CESSNA SB No CQB 85-25R1. Replacement parts must be NAS 1291-8 nuts purchased from the Cessna supply division after 22 November 1985. Compliance: 1. Within 10 hours time in service after 16 January 1986. 2. a. For applicable aircraft manufactured after 1 January 1984 or which have replaced the horizontal stabilizer after 1 January 1984 or which have replaced the front spar attachment bolt retaining nuts after 1 January 1984, within 10 hours time in service after 16 January 1986. 2. b. For all other applicable aircraft, within 100 hours time in service after 16 January 1986 or at the next scheduled inspection for Maintenance Release issue after 16 January 1986 whichever is the later. Background: The manufacturer reports that one or both of the horizontal stabilizer front spar attachment bolt retaining nuts may be broken or subject to failure due to hydrogen embrittlement.