Ad/EC 135/20 - Main Transmission Mast Bearing Retainer Bolts (Cth)

AIRWORTHINESS DIRECTIVE

For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.001(1) of CASR 1998.  The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.

Eurocopter EC 135 Series Helicopters

AD/EC 135/20 Main Transmission Mast Bearing Retainer Bolts 12/2008 TX

Applicability:

Eurocopter Deutschland GmbH (ECD) EC 135 P1(CDS), EC 135 P1(CPDS),
EC 135 P2(CPDS), EC 135 P2+, EC 135 T1(CDS), EC 135 T1(CPDS),
EC 135 T2(CPDS) and EC 135 T2+ helicopters.

Requirement:

1.    Inspect the attachment hardware and install locking washers in accordance with Section 3.B of ECD Alert Service Bulletin (ASB) No. EC135-63A-013
Revision 02.

2.    Unless accomplished as required by Requirement 1 of this AD, inspect the attachment hardware and install locking washers in accordance with Section 3.B of ECD ASB No. EC135-63A-013 Revision 02.

3.    For helicopters that have already been modified, prior to the effective date of this AD, in accordance with ECD ASB No. EC135-63A-013 at original issue or Revision 01; inspect the attachment hardware and install locking washers in accordance with Section 3.B of ECD ASB No. EC135-63A-013 Revision 02.

4.    Do not install a main transmission on a helicopter, unless it has been modified in accordance with Section 3.B of ECD ASB No. EC135-63A-013 Revision 02.

The use of later approved revisions of this document is acceptable for compliance with the requirements of this AD.

Note:  EASA Emergency AD 2008-0175-E dated 16 September 2008 refers.

Compliance:

For Requirement 1 - After the effective date of this AD, when unusual vibrations are detected during the start or the end phase of the main rotor’s running, within 3 flight cycles after detection.

For Requirement 2 - Within the next 50 flight hours (FH) after the effective date of this AD, but not later than 31 March 2009.

For Requirement 3 - Within 400 FH (+/- 10%) after the effective date of this AD.

For Requirement 4 - From the effective date of this AD.

This Airworthiness Directive becomes effective on 22 September 2008.

Background:

One operator has reported the occurrence of unusual vibrations during the start phase of the main rotor on one helicopter.  These vibrations stopped after the application of torque.  The troubleshooting accomplished by the maintenance personnel showed that six of the eight attachment screws of the lower hub-shaft bearing support had loosened.  After inspection of the affected operator’s fleet, the attachments screws of the lower hub-shaft bearing support were found loosened on the main transmissions of two additional helicopters.  The lower hub-shaft bearing consists of a ball bearing and a roller bearing.  The outer race of the roller bearing is fixed to the housing with screws.  Should all attachment screws become loose, the outer race of the roller bearing might separate, which would constitute an unsafe condition.  In such case, however, the axial guidance of the rotor hub-shaft would still be ensured.

For the reasons described above, this AD requires the inspection of the main transmission attachment hardware and installation of locking washers.

Charles Lenarcic
Delegate of the Civil Aviation Safety Authority

17 September 2008