AD/Dauphin/90 Main Rotor Mast Nut (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 SA 360 and SA 365 (Dauphin) Series Helicopters

AD/DAUPHIN/90 Main Rotor Mast Nut 2/2007 DM

Applicability:

Model SA 365 N, SA 365 N1, AS 365 N2, and AS 365 N3 helicopters, all serial numbers, fitted with a mast nut installed in main rotor mast assemblies, all part numbers.

Requirement:

1.    For main rotor mast assemblies having logged less than 1,600 flight hours since new or complete overhaul:

Inspect the mast nut using a light source or a boroscope if MOD 0762B33 or MOD 0762B69 is not embodied, or using a boroscope if MOD 0762B33 or MOD 0762B69 is embodied, in accordance with paragraph 2.B. of Eurocopter AS 365 Alert Service Bulletin No. 62.00.23.

2.    For main rotor mast assemblies having logged more than 1,600 flight hours since new or complete overhaul:

Inspect the mast nut using a light source or a boroscope if MOD 0762B33 or MOD 0762B69 is not embodied, or using a boroscope if MOD 0762B33 or MOD 0762B69 is embodied, in accordance with paragraph 2.B. of Eurocopter AS 365 Alert Service Bulletin No. 62.00.23.

If a crack/failure of the mast nut is detected during any inspection, before further flight, remove and replace the rotor mast nut in accordance with paragraph 2.B.2 of Eurocopter AS 365 Alert Service Bulletin No. 62.00.23.

Note:  EASA Emergency AD 2006-0368-E refers.

Compliance:

1.    At the latest, at 1,650 flight hours since new or complete overhaul, and thereafter at intervals not to exceed 1,650 flight hours.

2.    Within 50 flight hours after 11 December 2006, and thereafter at intervals not to exceed 1,650 flight hours.

This Airworthiness Directive becomes effective on 11 December 2006.

Background: The partial failure of a main rotor mast nut was detected during a main rotor mast complete overhaul.  Investigation revealed the crack origin was related to circular scoring of the nut threads.  Complete failure of the mast nut could lead to the loss of the helicopter.

David Villiers
Delegate of the Civil Aviation Safety Authority

7 December 2006