# ASB MBB-BK117-60A-126

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

## 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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# ASB MBB-BK117-60A-126

PAGE 2 of 7 Revision 0, 2013-06-24 

## 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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# ASB MBB-BK117-60A-126

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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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# ASB MBB-BK117-60A-126

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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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# ASB MBB-BK117-60A-126

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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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# ASB MBB-BK117-60A-126

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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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# ASB MBB-BK117-60A-126

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

## 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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