ERRATA CORRIGE

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

n°109-136 .

PAGE 5 “STEP N° 3”

Was:

3.In accordance with the figure 1 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 A109A/AII Maintenance Manual or A109C Maintenance Manual and the 

figures 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° 109-136

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 10

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 A109A, A109AII and A109C 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° 20 (A109A) or n°16 (A109AII/C) nuts MS21042L4 installed on the 

tail rotor drive shaft line (PART I) and the necessary instructions to 

ALERT

ALERT
B.T. 109-136

Page 2 of 10

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 is required to apply this Bollettino:

P/N DENOMINATION Q.TY NOTE

NAS1805-4 Nut 20 (1)

NAS1805-4 Nut 16 (2)

NOTE

(1) Applicable for A109A

(2) Applicable for A109AII / A109C 

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:

A109A/AII Maintenance Manual.

A109C Maintenance Manual.

A109A/AII Illustrated Parts Catalog.
B.T. 109-136

Page 3 of 10

A109C Illustrated Parts Catalog.

PUBLICATIONS AFFECTED:

A109A/AII Illustrated Parts Catalog.

A109C Illustrated Parts Catalog.

COMPLIANCE INSTRUCTIONS:

PART I:

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

disconnect any power supply, in accordance with the instructions 

given in the A109A/AII Maintenance Manual or A109C Maintenance 

Manual.

2. Gain access to the number 1÷4 drive shafts (A109A) or to the 

number 1÷3 drive shafts (A109AII/C), in accordance with the 

instructions given in the A109A/AII Maintenance Manual or A109C 

Maintenance Manual (Sections 65-31 and 52-00 (A109A/AII) or 65-

10 and 06-40 (A109C) ).

3. For A109A helicopters (See figure 1 and 2):

3.1. 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.

3.2. 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.

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

number 2 drive shaft for cracks.

NOTE

The use of a light source and a mirror is 

required. If any doubt remains, use an 

endoscope.

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

number 3 drive shaft for cracks.

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

adaptor splined for cracks.
B.T. 109-136

Page 4 of 10

NOTE

The use of a light source, a mirror and an 

endoscope is required. (See figure 5 for the 

access point).

4. For A109AII/C helicopters (See figure 3 and 4):

4.1. 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.

4.2. 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.

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

number 2 drive shaft for cracks.

4.5. 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 5 for the 

access point).

5. 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.

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

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

that the work area is clean.

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

removed/opened during point 2 in accordance with the instructions 

given in the A109A/AII Maintenance Manual or A109C Maintenance 

Manual (Section 52-00 (A109A/AII) 06-40 (A109C) ).

9. Return the helicopter to a ready to flight condition.
B.T. 109-136 

Page 5 of 10 

10. 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 A109A/AII Maintenance Manual or A109C Maintenance 

Manual . 

2. Gain visual access to the number 1÷4 drive shaft (A109A) and to 

the number 1÷3 drive shaft (A109AII/C), in accordance with the 

instructions given in the A109A/AII Maintenance Manual or A109C 

Maintenance Manual (Sections 65-31 and 52-00 (A109A/AII) or 65-

10 and 06-40 (A109C) ). 

3. In accordance with the figure 1 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 

A109A/AII Maintenance Manual or A109C 

Maintenance Manual (Section 52-00 

(A109A/AII) 06-40 (A109C) ). 

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

that the work area is clean. 

5. Install the access panel and close the access doors previously 

removed/opened in accordance with the instructions given in the 

A109A/AII Maintenance Manual or A109C Maintenance Manual 

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

y 1

6

b

09-13 EC
B.T. 109-136

Page 5 of 10

10. 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 A109A/AII Maintenance Manual or A109C Maintenance 

Manual .

2. Gain visual access to the number 1÷4 drive shaft (A109A) and to 

the number 1÷3 drive shaft (A109AII/C), in accordance with the 

instructions given in the A109A/AII Maintenance Manual or A109C 

Maintenance Manual (Sections 65-31 and 52-00 (A109A/AII) or 65-

10 and 06-40 (A109C) ).

3. In accordance with A109A/AII Maintenance Manual or A109C 

Maintenance Manual and the figures 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 

A109A/AII Maintenance Manual or A109C 

Maintenance Manual (Section 52-00 

(A109A/AII) 06-40 (A109C) ).

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

that the work area is clean.

5. Install the access panel and close the access doors previously 

removed/opened in accordance with the instructions given in the 

A109A/AII Maintenance Manual or A109C Maintenance Manual

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. 109-136

Page 6 of 10

FIGURE 1

That figure is representative, for more details ref. to Pertinent Maintenance Manual
B.T. 109-136

Page 7 of 10

FIGURE 2

That figure is representative, for more details ref. to Pertinent Maintenance Manual
B.T. 109-136

Page 8 of 10

FIGURE 3

That figure is representative, for more details ref. to Pertinent Maintenance Manual
B.T. 109-136

Page 9 of 10

FIGURE 4

That figure is representative, for more details ref. to Pertinent Maintenance Manual
B.T. 109-136

Page 10 of 10

DETAIL A

FIGURE 5

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.