Document ID: chunk:federal_register_of_legislation:F2006B02148:body:0:p2
Version: federal_register_of_legislation:F2006B02148
Segment Type: other
Provision Reference: 
Character Range: 2648–3935

continued flight with the defective straps on caps, must be supported by a though fatigue and residual strength evaluation.

               Compliance: Complete the inspections not later than 31 March 1992. If micro structure of the main spar lower cap is susceptable to stress corrosion (AD/AC/86 refers) repair or replace the defective straps before further flight.
 COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY
 SCHEDULE OF AIRWORTHINESS DIRECTIVES

           Background:  Very severe corrosion has been found in the internal steel strap of an Australian- registered aircraft. The strap was made from 4130 steel, not 301 stainless as the design records indicate. Twin Commander has advised that there may be up to 200 other aircraft with 4130 steel straps, but there are unfortunately no production records. At least one corroded 4130 has be found in the USA.

           The 4130 steel straps, unprotected, are very prone to corrosion. A corroded strap could seriously degrade the durability of the main spar assembly.

           This Directive has been issued to protect the Australian fleet in the short term. Twin Commander are developing a more permanent solution, to be published in a forthcoming service bulletin.