ERRATA CORRIGE

Please find here attached the page that have to be replaced in the basic Bollettino Tecnico 

n°109K-58 .

PAGE 4 “STEP N° 3”

Was:

3.In accordance with the figure 1 and 2 remove the nuts MS21042L4 and replace it with nuts 

NAS1805-4. Torque the nuts NAS1805-4 to 5.6 thru 7.9 N m “.....9. N6603-2 BOLT

Became:

3 In accordance with A109K2 Maintenance Manual and the figure 1 and 2 remove the nuts 

MS21042L4 and replace it with nuts NAS1805-4. Torque the nuts NAS1805-4 to 5.6 thru 7.9 N 

m “.....9. NAS1149C0332R WASHER

 10. NAS6603-2 BOLT
AgustaWestland S.p.A

Via Giovanni Agusta, 520

21017 Cascina Costa di Samarate (VA) Italy

Tel.: +39 0331 229111 - Fax: +39 0331 229605/222595

MANDATORY

An appropriate entry should be made in the aircraft log book upon accomplishment.

If ownership of aircraft has changed, please, forward to new owner.

TRANSLATION OF 

BOLLETTINO TECNICO 

N° 109K-58

The technical content of this document is approved 

under the authority of DOA nr EASA.21J.005. 

DATE September 20, 2013

REV. A April 07, 2011 

Compliance with 

this bollettino is: 

 ALERT Page 1 of 7

SUBJECT: ONE TIME INSPECTION OF THE NUTS MS21042L4 ON THE TAIL 

ROTOR DRIVE SHAFT LINE AND SUBSEQUENT REPLACEMENT 

WITH THE NUTS NAS1805-4.

REASON: Provide the necessary instructions to perform a one time visual 

inspection for possible presence of cracks on nuts MS21042L4 installed 

on the tail rotor drive shaft line (PART I) and subsequent replacement 

with nuts NAS1805-4 (PART II).

HELICOPTERS AFFECTED:

All the Agusta A109K2 helicopters.

COMPLIANCE:

PART I:

At receipt of this Bollettino and before the next flight

PART II:

Within and not later than the next 10FH/30 days after the application of 

the PART I of this Bollettino.

DESCRIPTION:

On two in service AW109SP helicopters, during scheduled inspection on 

the tail rotor drive shaft line, one nut MS21042L4 that connect the 

Thomas coupling with the splined adapter was found cracked.

The performed investigations have revealed that the crack reported on 

the nut is due to a production deficiency (causing hydrogen 

embrittlement) from the standard nut supplier.

This Bollettino is issued in order to provide the necessary instructions to

perform a one time visual inspection to verify the presence of cracks on 

the n°16 nuts MS21042L4 installed on the tail rotor drive shaft line

ALERT

ALERT
B.T. 109K-58

Page 2 of 7

(PART I) and the necessary instructions to replace, on the tail rotor drive 

shaft line, the nuts MS21042L4 with the nuts NAS1805-4 (PART II).

REQUIRED MANPOWER:

PART I:

An estimated 2 manpower hours are required for compliance with this 

Part of this Bollettino.

PART II:

An estimated 16 manpower hours are required for compliance with this 

Part of this Bollettino

WARRANTY:

Within the calendar terms mentioned at point “Compliance”, the parts 

required to apply the present Bollettino shall be supplied on a free of 

charge basis by AgustaWestland S.p.A. upon Customer’s request, with 

the exception for Consumable materials and Tools; all the parts required 

after the “Compliance date” will be dispatched on charge basis for the 

Customer. 

Upon application of this Bollettino, destroy locally the removed parts.

REQUIRED MATERIALS:

The following material may be required to apply this Bollettino:

P/N DENOMINATION Q.TY

NAS1805-4 Nut 16.

SPECIAL TOOLS:

The following special tool could be required for compliance with this 

Bollettino:

P/N DENOMINATION

Commercial Endoscope GE Inspection Tecnologies 

Model: XL Go A3920 with 4.0 

mm diameter and 2 m length 

probe (or equivalent)

WEIGHT AND BALANCE CHANGES:

N.A.

REFERENCES:

A109K2 Maintenance Manual .

A109K2 Illustrated Parts Catalog

PUBLICATIONS AFFECTED:

A109K2 Illustrated Parts Catalog
B.T. 109K-58

Page 3 of 7

COMPLIANCE INSTRUCTIONS:

(See figure 1 to 3)

PART I:

1. Prepare the helicopter on ground for a safe maintenance,

disconnect any power supply, in accordance with the instructions 

given in the A109K2 Maintenance Manual.

2. Gain access to the number 1 drive shaft, the number 2 drive shaft 

and the number 3 drive shaft, in accordance with the instructions 

given in the A109K2 Maintenance Manual (Sections 65-10 and 06-

40).

3. Inspect the four nuts connecting the number 1 drive shaft with the 

adaptor splined for cracks.

NOTE

The use of a light source and a mirror is 

required. If any doubt remains, use an 

endoscope.

4. Inspect the four nuts connecting the number 2 drive shaft with the 

number 1 drive shaft for cracks.

NOTE

The use of a light source and a mirror is 

required. If any doubt remains, use an 

endoscope.

5. Inspect the four nuts connecting the number 2 drive shaft with 

number 3 drive shaft for cracks.

6. Inspect the four nuts connecting the number 3 drive shaft with the 

adaptor splined for cracks.

NOTE

The use of a light source, a mirror and an 

endoscope is required. (See figure 3 for the 

access point).

7. If any crack is found, replace all the nuts MS21042L4 with the new 

NAS1805-4 nuts in accordance with the PART II of this Bollettino.

8. If no cracks are found proceed with the following steps.

9. Remove all the tools and other items from the work area. Make sure 

that the work area is clean.

10. Install all the access panels and close all the access doors 

removed/opened during point 2 in accordance with the instructions 
B.T. 109K-58

Page 4 of 7

given in the A109K2 Maintenance Manual (Sections 65-10 and 06-

40).

11. Return the helicopter to a ready to flight condition.

12. Record compliance with the PART I of this Bollettino in the 

helicopter log book.

PART II:

1 Prepare the helicopter on ground for a safe maintenance, 

disconnect any power supply, in accordance with the instructions 

given in the A109K2 Maintenance Manual .

2. Gain access to the number 1 drive shaft, the number 2 drive shaft 

and the number 3 drive shaft, in accordance with the instructions 

given in the A109K2 Maintenance Manual (Sections 65-10 and 06-

40).

3. In accordance with the figure 1 and 2 remove the nuts MS21042L4 

and replace it with nuts NAS1805-4. Torque the nuts NAS1805-4 to 

5.6 thru 7.9 N m.

NOTE 1

To avoid the disassembling of the Tail Rotor 

shaft is recommended to replace the nuts 

interested one at a time.

NOTE 2

To perform the replacement of the above 

mentioned nuts, it may be necessary to 

remove part of the tail rotor drive shaft line, in 

accordance with the instructions given in the 

A109K2 Maintenance Manual (Section65-

10).

4. Remove all the tools and other items from the work area. Make sure 

that the work area is clean.

5. Install all the access panels and close all the access doors 

removed/opened during point 2 in accordance with the instructions 

given in the A109K2 Maintenance Manual (Sections 65-10 and 06-

40).

6. Return the helicopter to a ready to flight condition.

7. Record compliance with the PART II of this Bollettino in the 

helicopter log book.

8. Send the attached compliance form to the following email box:

Aw109.mbx@agustawestland.com

P

S

ER EDE

AGE UP

S

D

b 109K-5 E

y

8 C
B.T. 109K-58

Page 4 of 7

given in the A109K2 Maintenance Manual (Sections 65-10 and 06-

40).

11. Return the helicopter to a ready to flight condition.

12. Record compliance with the PART I of this Bollettino in the 

helicopter log book.

PART II:

1 Prepare the helicopter on ground for a safe maintenance, 

disconnect any power supply, in accordance with the instructions 

given in the A109K2 Maintenance Manual .

2. Gain access to the number 1 drive shaft, the number 2 drive shaft 

and the number 3 drive shaft, in accordance with the instructions 

given in the A109K2 Maintenance Manual (Sections 65-10 and 06-

40).

3. In accordance with A109K2 Maintenance Manual and the figure 1 

and 2 remove the nuts MS21042L4 and replace it with nuts 

NAS1805-4. Torque the nuts NAS1805-4 to 5.6 thru 7.9 N m.

NOTE 1

To avoid the disassembling of the Tail Rotor 

shaft is recommended to replace the nuts 

interested one at a time.

NOTE 2

To perform the replacement of the above 

mentioned nuts, it may be necessary to 

remove part of the tail rotor drive shaft line, in 

accordance with the instructions given in the 

A109K2 Maintenance Manual (Section65-

10).

4. Remove all the tools and other items from the work area. Make sure 

that the work area is clean.

5. Install all the access panels and close all the access doors 

removed/opened during point 2 in accordance with the instructions 

given in the A109K2 Maintenance Manual (Sections 65-10 and 06-

40).

6. Return the helicopter to a ready to flight condition.

7. Record compliance with the PART II of this Bollettino in the 

helicopter log book.

8. Send the attached compliance form to the following email box:

Aw109.mbx@agustawestland.com
B.T. 109K-58

Page 5 of 7

FIGURE 1

ref. A109K2 Illustrated Parts Catalog

Section 65-10 TAIL ROTOR DRIVE SHAFT INSTL,FWD

N°1 SPLINED

ADAPTER

MS21042L4 NUT x 2

N°1 THOMAS

COUPLING

MS21042L4 NUT x 2

MS21042L4 NUT x 2

N°2 THOMAS

COUPLING

N°2 SPLINED

ADAPTER

MS21042L4 NUT x 2

N°3 SPLINED

ADAPTER

MS21042L4 NUT x 2

N°3 THOMAS

COUPLING

MS21042L4 NUT x 2
B.T. 109K-58

Page 6 of 7

FIGURE 2

ref. A109K2 Illustrated Parts Catalog

Section 65-10 DRIVE SHAFT AND 90 DEGREE GEARBOX INSTL

N°4 THOMAS

COUPLING

N°4 SPLINED

ADAPTER

MS21042L4 NUT x 2

MS21042L4 NUT x 2
B.T. 109K-58

Page 7 of 7

DETAIL A

FIGURE 3

For ref. Only

A

Note: 

Remarks:

Informazioni: 

Information:

Al fine di gestire le varianti alla configurazione base, in relazione all’emissione del Bollettino Tecnico, preghiamo di voler compilare il presente modulo in tutte le sue parti e spedirlo all’indirizzo sopra indicato. Si ringrazia per la gentile collaborazione data. 

We request your cooperation in filling this form, in order to keep out statistical data relevant to aircraft configuration up-to-date. The form should be filled in all 

its parts and sent to the above address. We thank you beforehand for the information given.

MODULO APPLICAZIONE BOLLETTINO TECNICO

TECHNICAL BULLETIN COMPLIANCE FORM

Data: 

Date:

Numero: 

Number:

Revisione: 

Revision:

Prego spedire a questo indirizzo: 

Please send to the following address: 

AGUSTAWESTLAND S.p.A. 

CUSTOMER SUPPORT & SERVICES - ITALY

PRODUCT SUPPORT ENGINEERING DPT.

Via del Gregge, 100

21015 Lonate Pozzolo (VA) - ITALY 

Tel.: +39 0331 664905

Fax: +39 0331 664684

Telefono: 

Telephone:

Fax:

Data Applicazione B.T.: 

B.T. Compliance Date:

Denominazione Cliente ed Indirizzo: 

Customer Name and Address:

Modello Elicottero 

Helicopter Model S/N Matricola Tail Number

Ore Totali 

Total Hours

Ore D.U.R. 

T.S.O.