EASA AD No : 2006-0368R1 

EASA Form 110 Page 1/4 

 

EASA AIRWORTHINESS DIRECTIVE 

AD No.: 2006-0368R1 

Corrected: 08 December 2010 

Date: 02 December 2010 

Note: This Airworthiness Directive (AD) is issued by EASA, acting in accordance with 

Regulation (EC) No 216/2008 on behalf of the European Community, its Member States and of 

the European third countries that participate in the activities of EASA under Article 66 of that 

Regulation. 

This AD is issued in accordance with EC 1702/2003, Part 21A.3B. In accordance with EC 2042/2003 Annex I, Part M.A.301, the 

continuing airworthiness of an aircraft shall be ensured by accomplishing any applicable ADs. Consequently, no person may operate 

an aircraft to which an AD applies, except in accordance with the requirements of that AD unless otherwise specified by the Agency 

[EC 2042/2003 Annex I, Part M.A.303] or agreed with the Authority of the State of Registry [EC 216/2008, Article 14(4) exemption]. 

Type Approval Holder’s Name : 

EUROCOPTER

Type/Model designation(s) : 

SA 365 N, AS 365 N, SA 366 and EC 155 

helicopters 

TCDS Number: France N° 159 

Foreign AD: Not applicable 

Revision: This AD revises EASA AD 2006-0368-E dated 06 December 2006. 

ATA 62 Rotor – Rotor Mast Nut – Check / Replacement

Manufacturer(s): EUROCOPTER (Formerly EUROCOPTER – FRANCE, AEROSPATIALE) 

Applicability: SA 365 N, SA 365 N1, AS 365 N2, AS 365 N3, SA 366 G1, EC 155 B and 

EC 155 B1 helicopters, all serial numbers, fitted with a mast nut Part Number 

(P/N) 360A31-1020-20 installed in main rotor mast assemblies. 

Note:

This AD does not apply to helicopters that have modifications (MOD) 0762B88 

and/or MOD 0762C42 embodied in-production or EUROCOPTER Service 

Bulletin No. 62-007 embodied in service as applicable to helicopter type. 

Embodiment of these modifications consists in replacement of mast nut P/N 

360A31-1020-20 by mast nut P/N 365A31-2060-20 or P/N 365A31-2060-21, as 

applicable to helicopter type. 

Reason: A cracked (partially failed) main rotor mast nut was discovered during a 

complete overhaul of a main rotor mast. The start of the crack was related to 

circular scoring found in the nut threads. 

This condition, if not detected and corrected, could lead to complete failure of 

the mast nut, possibly resulting in failure of the rotor mast and consequent loss 

of control of the helicopter. 

To address this unsafe condition, EASA issued Emergency AD 2006-0368-E to 

require repetitive inspections of the mast nut and, depending on findings, 

corrective actions. 
EASA AD No : 2006-0368R1 

EASA Form 110 Page 2/4 

 

Since issuance of EASA AD 2006-0368-E, EUROCOPTER has developed 

MOD 0762C42 to improve the strength of the mast nut by changing its material. 

The embodiment of MOD 0762C42 or the in-service replacement of mast nut 

P/N 360A31-1020-20 by mast nut P/N 365A31-2060-20 or P/N 365A31-2060-

21 (as applicable to helicopter type) constitutes an optional terminating action to 

the repetitive inspection requirements of this AD. For this reason, EASA AD 

2006-0368-E is revised to inform which helicopters remain subject to 

inspections and replacement requirements of this AD. 

This AD is republished to correct a typographical error in the replacement mast 

nut part numbers referenced in this AD. 

Effective Date: Revision 1: 16 December 2010. 

Original issue: 08 December 2006. 

Required action(s) 

and Compliance 

Time(s): 

The following measures are rendered mandatory from 08 December 2006 [the 

effective date of the original issue of this AD]: 

(1) SA 365 N, SA 365 N1, AS 365 N2 and AS 365 N3 helicopters. 

 (1.1).Main rotor mast assemblies having logged less than 1,600 flight hours 

since new or complete overhaul. 

 At the latest at 1,650 flight hours since new or complete overhaul, then at 

intervals not exceeding 1,650 flight hours, inspect the mast nut using a light 

source or a borescope if MOD 0762B33 or MOD 0762B69 is not embodied 

or using a borescope if MOD 0762B33 or MOD 0762B69 is embodied, to 

ensure that there is no crack or failure in the mast nut, in compliance with 

the instructions specified in paragraph 2.B of EUROCOPTER AS 365 Alert 

Service Bulletin (ASB) No. 62.00.23 referenced below. 

 (1.2). Main rotor mast assemblies having logged more than 1,600 flight 

hours since new or complete overhaul: 

 No later than within 50 flight hours, then at intervals not exceeding 1,650 

flight hours, inspect the mast nut using a light source or a borescope if

MOD 0762B33 or MOD 0762B69 is not embodied or using a borescope if

MOD 0762B33 or MOD 0762B69 is embodied, to ensure that there is no 

crack or failure in the mast nut, in compliance with the instructions specified 

in paragraph 2.B of EUROCOPTER AS 365 ASB No. 62.00.23 referenced 

below. 

(2) SA 366 G1 helicopters: 

 (2.1) Main rotor mast assemblies having logged less than 960 flight hours 

since new or complete overhaul: 

 At the latest at 990 flight hours since new or complete overhaul, then at 

intervals not exceeding 990 flight hours, inspect the mast nut using a light 

source or a borescope if MOD 0762B33 or MOD 0762B69 is not embodied 

or using a borescope if MOD 0762B33 or MOD 0762B69 is embodied, to 

ensure that there is no crack or failure in the mast nut, in compliance with 

the instructions specified in paragraph 2.B of EUROCOPTER SA 366 ASB

No. 62.12 referenced below. 

 (2.2). Main rotor mast assemblies having logged more than 960 flight hours 

since new or complete overhaul: 

 No later than within 30 flight hours, then at intervals not exceeding 990 

flight hours, inspect the mast nut using a light source or a borescope if 

MOD 0762B33 or MOD 0762B69 is not embodied or using a borescope if 

MOD 0762B33 or MOD 0762B69 is embodied, to ensure that there is no 

crack or failure in the mast nut, in compliance with the instructions specified 

in paragraph 2.B of EUROCOPTER SA 366 ASB No. 62.12 referenced 

below. 
EASA AD No : 2006-0368R1 

EASA Form 110 Page 3/4 

 

(3) EC 155 B and EC 155 B1 helicopters: 

 (3.1) Main rotor mast assemblies (pre MOD 0762B88 or not modified in 

accordance with SB No. 62-007), having logged less than 610 flight hours 

since new: 

 At the latest at 660 flight hours since new, then at intervals not exceeding 

660 flight hours, inspect the mast nut using a borescope to ensure that 

there is no crack or failure in the mast nut, in compliance with the 

instructions specified in paragraph 2.B of EUROCOPTER EC 155 Alert 

Service Bulletin (ASB) No. 62A014 referenced below.

 (3.2) Main rotor mast assemblies (pre MOD 0762B88 or not modified in 

accordance with SB No. 62-007), having logged more than 610 flight hours 

since new: 

 No later than within 50 flight hours, then at intervals not exceeding 660 

flight hours, inspect the mast nut using a borescope to ensure that there is 

no crack or failure in the mast nut, in compliance with the instructions 

specified in paragraph 2.B of EUROCOPTER EC 155 Alert Service Bulletin 

(ASB) No. 62A014 referenced below. 

(4) Interpretation of the results: 

(4.1) If, during any of the inspections as required by this AD, a crack / 

failure is found in the mast nut, before next flight, remove and replace the 

rotor mast nut, in accordance with the instructions specified in paragraph 

2.B.2 of the referenced ASB corresponding to the helicopter version. 

(4.2) Replacement of the mast nut as required by paragraph (4.1) of this 

AD does not constitute terminating action for the repetitive inspections 

required by this AD. 

(5) Optional terminating action: 

Modification of a helicopter by replacing rotor mast nut P/N 360A31-1020-

20 with rotor mast nut P/N 365A31-2060-20 or P/N 365A31-2060-21, as 

applicable to helicopter type, constitutes terminating action for the repetitive 

inspection requirements of this AD for that helicopter. 

Ref. Publications: EUROCOPTER AS 365 Alert Service Bulletin No. 62.00.23 original issue dated 

22 November 2006 and revision 1 dated 27 October 2010, 

EUROCOPTER SA 366 Alert Service Bulletin No. 62.12 original issue dated 22 

November 2006 and revision 1 dated 27 October 2010,

EUROCOPTER EC 155 Alert Service Bulletin No. 62A014 original issue dated 

22 November 2006 and revision 1 dated 27 October 2010, 

EUROCOPTER EC 155 Service Bulletin No. 62-007 original issue dated 02 

March 2006. 

The use of later approved revisions of these documents is acceptable for 

compliance with the requirements of this AD. 

Remarks : 1. If requested and appropriately substantiated, EASA can approve 

Alternative Methods of Compliance for this AD. 

2. The required actions and the risk allowance have granted the issuance of a 

Final AD with Request for Comments, postponing the public consultation 

process after publication. 

3. Enquiries regarding this AD should be referred to the Airworthiness 

Directives, Safety Management & Research Section, Certification 

Directorate, EASA. E-mail: ADs@easa.europa.eu. 
EASA AD No : 2006-0368R1 

EASA Form 110 Page 4/4 

 

4. For any question concerning the technical content of the requirements in 

this AD, please contact: EUROCOPTER (STDI) - Aéroport de Marseille 

Provence 13725 Marignane Cedex - France. Tel: 33 (0) 4 42 85 97 97 - 

Fax: 33 (0) 4 42 85 99 66. 

E-mail: Directive.technical-support@eurocopter.com.