European Aviation Safety Agency

ATA 67 - Rotors Flight Control – Tail Rotor Control Stop Screws – Modification - Comment Period Expires July 22, 2015
 N PAD 15-087

Annotation

Reason:

During take-off with a sling load, the pilot of an AS350 B3 helicopter noticed that he reached one of the yaw stops before its usual position. The subsequent inspection revealed that a nut of the tail rotor control stop was loose and that the corresponding tail rotor control stop screw was out of adjustment.

This condition, if not detected and corrected, can lead to the loss of adjustment of the affected stop and consequently limit yaw authority, possibly resulting in loss of control of the helicopter.

To address this potential unsafe condition, Eurocopter issued Alert Service Bulletin (ASB) AS350-05.00.64 and ASB AS355-05.00.59 to provide inspection instructions. Consequently, as an interim measure, pending development of a final solution, EASA issued AD 2011-0164 to require repetitive inspections of the tail rotor control stop screws and, depending on findings, adjustment.

Since that AD was issued, Airbus Helicopters (AH) developed MOD 074602, which consists of installing a dual mechanical safety on primary yaw stops, and published ASB AS350-67.00.61 and ASB AS355-67.00.42 to provide modification instructions. In addition, it was discovered that not all affected helicopters were identified in the inspection ASBs, which have therefore been revised accordingly.

For the reasons described above, this AD retains the requirement of EASA AD 2011-0164, which is superseded, redefines the Applicability, and requires modification of the primary yaw stops, which constitutes terminating action for the repetitive inspections required by this AD.