September 23, 2008 ASB-MBB-BK117-30-113

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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 lever
ASB-MBB-BK117-30-113 September 23, 2008

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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

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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).
ASB-MBB-BK117-30-113 September 23, 2008

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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

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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

2X2

3X2

3X2
ASB-MBB-BK117-30-113 September 23, 2008

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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.