COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Eurocopter EC 120 Series Helicopters AD/EC 120/1 Tail Gearbox - Load Measurements 6/99 DM Applicability: All EC120B helicopters equipped with tail gearbox part number: C652A010 1051 or C652A010 1052 with the following serial numbers: M101 - M124 (incl) and M126. Requirements: 1. Remove the tail rotor hub and the tail gearbox and measure the operating load of the pitch change control rod in accordance with instructions in para 2B(1) of EUROCOPTER EC120 Service Bulletin No. 01.001. 2. Reinstall the tail gearbox and tail rotor hub in accordance with manufacturer's instructions (work cards 65.21.00, 4-2 and 64.21.00, 4-2 resp). 3. Replace the tail gearbox with a compliant gearbox (ie. a gearbox with non applicable serial number or one which has acceptable operating loads in accordance with 1. Above). Note: DGAC AD 1999-151-001(A) dated 07 April 1999 refers. Compliance: 1. Within 50 flying hours of the effective date of this Directive but no later than 30 September 1999. 2. If loads measured at requirement 1 above are equal to or less than 1.2 daN. 3. Prior to next flight if loads measured are greater than 1.2 daN, This Airworthiness Directive becomes effective on 12 May 1999. Background: In service experience has detected a case of significant binding of the tail rotor pitch change control rod which could lead to loss of control of the aircraft. This Directive introduces tests on certain Tail Gearboxes to identify defective assemblies.