ASB MBB-BK117-60A-126

Revision 0, 2013-06-24 PAGE 1 of 7

Valid for Version(s): A-1, A-3, A-4,

B-1, B-2, C-1

ALERT SERVICE BULLETIN

SUBJECT: POWER PLANT -- N2 Controls --

Visual inspection of the N2 control arm

Revision No. Date of issue

Revision 0 2013-06-24

Summary:

Inspect the N2 control arm i.a.w. this Alert Service Bulletin.

Compliance:

Compliance with this Alert Service Bulletin is mandatory.

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1. PLANNING INFORMATION

1.A. EFFECTIVITY

1.A.1. Helicopters/installed equipment

(a) MBB-BK117

(b) Control arm P/N 117-63429-01 or

P/N 117-63429-05 or

P/N 117-63429-09

1.A.2. Non-installed equipment

Not applicable.

1.B. ASSOCIATED REQUIREMENTS

Not applicable.

1.C. REASON

Eurocopter was informed about an in-service event on a MBB-BK117 C-2 where the aircrew

noticed a drop of the rotor RPM (NR) within the green range, but could not beep it back to the

nominal value. An inspection of the Engine N2 control system revealed a heavily corroded and

broken control arm. This broken control arm was responsible for the loss of the engine droop

compensation. For this reason the Safety Information Notice 2483-S-76 was published.

Further analysis revealed that a broken control arm can cause under unfavorable conditions a

significant and non recoverable drop in rotor rpm depending on flight condition and power

demand.

Therefore, this Alert Service Bulletin specifies a first time visual inspection and a periodical

12-MONTHS INSPECTION of the N2 control arm.

1.D. DESCRIPTION

Remove the transmission cowlings. Visual inspect the N2 control arm. Install the transmission

cowlings.

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1.E. COMPLIANCE

1.E.1. Compliance at the works

Helicopters/installed equipment:

Not applicable.

Non-installed equipment:

Not applicable.

1.E.2. Compliance in service

Helicopters/installed equipment:

(a) The first time visual inspection of the N2 control arm i.a.w. Section 3.B must be

accomplished within the next 4 weeks after receipt of this Alert Service Bulletin.

(b) The visual inspection of the N2 control arm i.a.w. Section 3.B must be accomplished

together with every 12-MONTHS INSPECTION. Until the inspection is incorporated in the

MM, proceed i.a.w. Section 3.B of this Alert Service Bulletin.

Non-installed equipment:

Not applicable.

1.F. APPROVAL

Approval of this document:

The technical content of this document is approved under the authority of

DOA No. EASA.21J.034

1.G. MANPOWER

Qualification Mechanic Electrician Pilot Others

Time for the visual

inspection of N2

control arm

approx. 1 h -- -- --

1.H. WEIGHT AND BALANCE

Not applicable.

1.I. EFFECT ON ELECTRICAL LOADS

Not applicable.

1.J. SOFTWARE MODIFICATION EMBODIMENT RECORD

Not applicable.

1.K. REFERENCES

MM MBB-BK117 A-B

MM MBB-BK117 C-1

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1.L. DOCUMENTS AFFECTED

The changes to MM MBB-BK117 A-B / MM MBB-BK117 C-1 which are required as a result of this

Alert Service Bulletin will be incorporated with the following revisions:

MM MBB-BK117 A-B - Revision 43

MM MBB-BK117 C-1 - Revision 26

1.M.INTERCHANGEABILITY OR MIXABILITY OF PARTS

Interchangeability:

Not applicable.

Mixability:

Not applicable.

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2. MATERIAL INFORMATION

2.A. MATERIAL: PRICE - AVAILABILITY - PROCUREMENT

Not applicable.

2.B. INFORMATION CONCERNING INDUSTRIAL SUPPORT

Not applicable.

2.C. MATERIAL REQUIRED FOR EACH HELICOPTER/COMPONENT

Not applicable.

2.D. MATERIAL TO BE RETURNED

Not applicable.

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3. ACCOMPLISHMENT INSTRUCTIONS

3.A. GENERAL

Not applicable.

3.B. OPERATIONAL PROCEDURE

CAUTION

MAKE SURE THAT YOU EXAMINE ALL SIDES OF THE

COMPONENTS OF THE N2 CONTROLS USE A

FLASHLIGHT AND A MIRROR TO HELP YOU DO THE

INSPECTION. THE N2 CONTROLS ARE A SYSTEM

IMPORTANT FOR THE PROPER AND SAFE

OPERATION OF THE HELICOPTER.

3.B.1. Prelimanary steps:

(a) Disconnect battery and EPU (external power unit) from aircraft electrical system.

(b) Remove the transmission cowling i.a.w. MM, chapter 22-9.

3.B.2. Inspect the N2 control arm for damage and corrosion i.a.w. Figure 1:

(a) If no signs of damage and/or corrosion are detected, proceed i.a.w. Section 3.B.3.

(b) If signs of damage and/or corrosion are found:

-- Replace parts in the case of suspicion of exfoliation corrosion

-- Remove corrosion and/or scratches that are less than 0.5 mm (0.020 in) in depth

and repair surface i.a.w. Standard Practices Manual MTC 20-04-03-401.

-- Replace the parts with damage and/or corrosion and scratches that are more than

0.5 mm (0.020 in) in depth i.a.w. MM, chapter 65-12 / 65-14.

3.B.3. Final steps:

(1) Install the transmission cowling i.a.w. MM, chapter 22-11.

3.C. IDENTIFICATION

Identification of this document:

Confirm accomplishment of this Alert Service Bulletin by an entry in the historical record of the

helicopter.

3.D. OPERATING AND MAINTENANCE INSTRUCTIONS

The inspections i.a.w. Section 3.B of this Alert Service Bulletin must be repeated together with

the accomplishment of every 12-MONTHS INSPECTION until this Alert Service Bulletin is

incorporated in the MM MBB-BK117 A-B / MM MBB-BK117 C-1.

After accomplishment of the first time inspection and receipt of the (MM MBB-BK117 A-B -

Revision 43 / MM MBB-BK117 C-1 - Revision 26) this Alert Service Bulletin is no longer effective.

4. APPENDIX

Not applicable.

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Inspection N2 control arm

Figure 1

Mirror

N2 control arm N2 control arm

Example of a control arm showing exfoliation corrosion.

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