September 23, 2008 ASB-MBB-BK117-30-113 Page 1 of 6 1. PLANNING 1.A. Effectivity 1.A.1. Helicopters affected: All MBB BK117 of models A-1 to C-1. 1.A.2. Components affected: Balance weight 117-31714.07 or 117-31715.01 or 117-31720.01 or 117-31730.02 Control lever 117-31730 or 117-317361 or 105-31736 1.A.3. Spare Parts affected: Not applicable. 1.B. Reason During a periodical inspection corrosion was detected on the tail rotor balance weights in the area of the thread. At an advanced stage, this corrosion could possibly destroy the threads. In order to be able to recognize this damage and to replace the damaged components, a visual inspection is introduced with this Alert Service Bulletin. 1.C. Description Check balance weights and control levers on tail rotor. Replace damaged balance weights and control levers. 1.D. Compliance 1.D.1. Accomplish inspection of the balance weights and the control levers i.a.w. Section 2.B of this Alert Service Bulletin within the next 100 fh after receipt of this Alert Service Bulletin, but by 31.12.2008 at the latest. 1.D.2. After this, the inspection of the balance weights and the control levers must be regularily accomplished together with the “PERIODICAL INSPECTION”. 1.D.3. If damage is detected at the inspection i.a.w. Section 2.B.1.2 and/or 2.B.1.3 which is not within the admissible damage limits, replace the affected component before the next flight. **Date:** September 23, 2008 

# ALERT SERVICE BULLETIN **MBB-BK117**

**No.** ASB-MBB-BK117-30-113 **Subject:** Tail rotor – Check of balance weights and control leverSeptember 23, 2008 ASB-MBB-BK117-30-113 Page 2 of 6 1.E. Approval The technical content of this document is approved under the authority of DOA No. EASA.21J.034. 1.F. Manpower Requirement Approx. 4 man–hours. 1.G. Material, Cost and Availability See Section 3. 1.H. Special Tools (not applicable) 1.I. Mass and Moment (not applicable) 1.J. Reference Maintenance Manual MBB-BK 117 Maintenance Manual MBB-BK 117 C 1.K. Other Publications affected This Alert Service Bulletin will be incorporated in the following documents with one of the next revisions: – MM MBB-BK 117 – MM MBB-BK 117 C 1.L. Electrical Load Data (not applicable)September 23, 2008 ASB-MBB-BK117-30-113 Page 3 of 6 2. ACCOMPLISHMENT INSTRUCTIONS 2.A. Inspections Required (not applicable) 2.B. Work Procedure 2.B.1. Remove balance weights from control lever: **NOTE** Apply marks to the balance weights before they are removed in order to be able to re–establish the correct assignment and the old installation position towards the control lever when the balance weights are installed. 2.B.1.1. Remove cotter pins (3, Figure 1) and remove balance weights (2) from control lever (1). Discard cotter pins (3). 2.B.1.2. Check balance weights (1, Figure 2) for corrosion and/or mechanical damage: – If no corrosion or mechanical damage is detected in the thread area and on the cylindrical mating surfaces of the balance weights, proceed i.a.w. Section 2.B.1.3. – If damage to the threads on less than 25 percent of the respective thread is detected, the balance weights can be easily screwed and the cylindrical mating surfaces are not damaged, remove corrosion using suitable means. Proceed i.a.w. Section 2.B.1.3. – If damage to the threads on more than 25 percent of the respective thread is detected or the cylindrical mating surfaces are extensively damaged, replace balance weights before the next flight. Proceed i.a.w. Section 2.B.1.3. 2.B.1.3. Check control lever (2, Figure 2) for corrosion and/or mechanical damage: – If no corrosion or mechanical damage is detected, proceed i.a.w. Section 2.B.2. – If mechanical damage and/or corrosion is detected, polish out damage using polishing cloth 600. – If a depth of a maximum of 0.3 mm is not exceeded when polishing out and the diameter of the control lever is not less than a minimum measure of 9.95 mm, proceed i.a.w. Section 2.B.2. – If a depth of 0.3 mm is exceeded when polishing out and/or the diameter of the control lever in the transition area towards the thread is less than a minimum measure of 9.95 mm, replace control lever before the next flight. 2.B.2. Install balance weights to control lever: **NOTE** Ensure during installation of the balance weights that the balance weights are correctly assigned and installed to the control lever i.a.w. the applied marks. 2.B.2.1. Apply corrosion preventive paste (CM 518) onto thread of control lever (1, Figure 1).September 23, 2008 ASB-MBB-BK117-30-113 Page 4 of 6 2.B.2.2. Unscrew balance weights (2, Figure 1) until the positon on the control lever (1) that was marked at the removal has been reached. Secure balance weights (2) using new cotter pins (3). **NOTE** If vibrations on the tail rotor are detected during operation of the helicopter, balance tail rotor i.a.w. AMM, Chapter 33-3. 2.B.3. Confirm accomplishment of this Alert Service Bulletin by an entry in the historical record of the helicopter. 2.C. Conclusions (not applicable)

3. MATERIAL INFORMATION 3.1. Required Parts : No. Qty Nomenclature Part No.

1 2 Cotter pin** LN9430022 2 *a.n. Corrosion preventive paste (CM 518) * Consumable material, to be ordered from the Interturbine company. **Standard part, item must be separately ordered as needed.September 23, 2008 ASB-MBB-BK117-30-113 Page 5 of 6 Tail Rotor Balance Weights Figure 1 1 Control lever 2 Balance weight 3 Cotter pin LN94-30022 Apply corrosion preventive paste (CM 518) onto thread. 1

1 2X2

2 X2 3X2

3X2September 23, 2008 ASB-MBB-BK117-30-113 Page 6 of 6 Inspection of Balance Weights and Control Lever Figure 2 1 Balance weight 2 Control lever 1

1 2

Check areas for corrosion and/or mechanical damage.