Metro Aviation, Inc. ASB Number: MA145-21B-003

Rev. B, 20 December 2013 Page 1 of 5 MA145-21B-003

MBB-BK 117 C-2 (EC145)

ALERT SERVICE BULLETIN

SUBJECT: TAIL ROTOR SYSTEM 

AIR CONDITIONING DRIVE PULLEY ATTACHMENT

Revision Number Issue Date

IR 23 April 2013

A 26 April 2013

B 20 December 2013

Summary:

Revision B of the Alert Service Bulletin details the procedure to install dual locking tabs 

on the existing EC145 air conditioning drive pulley attachment bolts.

Reason for Revision:

Please replace Revision A of Alert Service Bulletin MA145-21A-003 with Revision B 

(MA145-21B-003).

Compliance:

Compliance with this Alert Service Bulletin is prescribed in Section 1.E
Metro Aviation, Inc. ASB Number: MA145-21B-003

Rev. B, 20 December 2013 Page 2 of 5 MA145-21B-003

MBB-BK 117 C-2 (EC145)

ALERT SERVICE BULLETIN

Air-Conditioning – Installation of Air-Conditioning Drive Pulley

1. Planning Information

A) Effectivity

i) Helicopters affected: Eurocopter MBB-BK 117 A-3, A-4, B-1, and C-2 (EC145) 

helicopters equipped with a Metro Aviation vapor-cycle air-conditioning kit P/N

117MM-100-2 STC#SH3880SW.

ii) Components affected: Metro Aviation vapor-cycle Air Conditioning drive pulley.

iii) Spare Parts affected: Not Applicable.

B) Concurrent Requirements: Not Applicable.

C) Reason: To improved bolt retention with dual locking features

D) Description: This Alert Service Bulletin details the procedure to install a dual locking 

tab on the existing EC145 air conditioning drive pulley attachment bolts.

E) Compliance: 

It is recommended that this service bulletin be incorporated within the next 10 flight 

hours. This Service Bulletin supersedes ASB MA145-21A-003.

NOTE: Compliance times are for aircraft operating time not Air Conditioner

operating time.

F) Approval: Engineering aspects are approved by the FAA.

G) Manpower: Approximately 4.0 man-hours are required to add dual lock tabs.

H) Weight and Balance: Not Applicable.

I) Electrical Load Data: Not Applicable.

J) Software Accomplishment Summary: Not Applicable.

K) References: Metro Aviation, MBB-BK 117 C-2 (EC145) Vapor Cycle Air-Conditioner 

Equipment Maintenance Manual (117MM-100-02) & Installation drawing (117M-600-2).

L) Other Publications affected: Not Applicable.
Metro Aviation, Inc. ASB Number: MA145-21B-003

Rev. B, 20 December 2013 Page 3 of 5 MA145-21B-003

M) Interchangeability of Parts: Not Applicable.

2. Material Information

A) Material: Three dual lock tabs (MAI-145-DUAL LOCK TAB) will be provided per aircraft 

at no cost until Dec. 31, 2014. Fax a purchase order referencing the aircraft serial 

number and Alert Service Bulletin number to Metro Aviation at (318) 698-5206.

B) Support Information: Not Applicable.

C) Material Necessary for Helicopter: 0.025” (0.62mm) stainless steel safety wire

D) Material to be Returned: Not Applicable.

3. Accomplishment Instructions

A) Remove Aircraft transmission and engine cowlings per AMM 71-11-00 Section 4-3 and 

4-4.

CAUTION: Do not remove the Air Conditioning drive pulley mount bolts without first 

relieving tension from compressor drive belt.

B) Remove one (of three) bolt sets that install the air conditioning compressor belt pulley to 

the rotor brake disc. Note; do not remove all three sets at the same time.

C) Discard AN960-416 washer (originally installed under head of bolt securing pulley to 

rotor disc).

D) Discard original lock tab P/N LN9023A10-1.4544.9

E) Install dual lock tab as shown below in View A-A. Reinstall bolts IAW EC145 

maintenance manual, Equipment Maintenance Manual 117MM-100-02, and drawing 

117M-600-2.

F) Bend any two tabs (“A” Tabs and “B” Tabs) on each bolt that do not interfere with safety 

wire hole being used to secure the brake rotor disk bolts, as shown in View B-B. The 

two tabs may be bent on the same side, or one each on opposing sides, as shown in 

Secondary Tab Bending. Bend down remaining single tab (tab “C”) as shown in View 

C-C.

G) Safety wire bolts (using 0.025” (0.6 mm) safety wire) as shown View B-B and IAW FAA 

AC 43.13 1B Chapter 7, Section 7, Paragraphs 7-122 through 7-125. Safety wire may 

wrap around bent tabs, as required.

H) Repeat above procedure for the remaining two sets of bolts (one bolt set as a time).

I) Reinstall Aircraft transmission and engine cowlings per AMM 71-11-00 Section 4-3 and 

4-4.
Metro Aviation, Inc. ASB Number: MA145-21B-003

Rev. B, 20 December 2013 Page 4 of 5 MA145-21B-003

FIG 1

COMPRESSOR BELT PULLEY

BOLT SET

(1 OF 3)

ROTOR BRAKE DISC

DUAL LOCK TAB

VIEW A-A

VIEW LOOKING FORWARD

SAFETY WIRE

(1 OF 3)
Metro Aviation, Inc. ASB Number: MA145-21B-003

Rev. B, 20 December 2013 Page 5 of 5 MA145-21B-003

“B” TABS

SECONDARY TAB BENDING

BENT TAB

BENT TAB

BENT TAB

BENT TAB

TAB “C”

BENT TABS

“A” TABS

BENT TABS BENT TAB

VIEW B-B

VIEW C-C

TAB “C”

ROTOR BRAKE DISC

COMPRESSOR BELT PULLEY

PRIMARY TAB BENDING

SAFETY WIRE

(1 OF 3)