Serrated lock washers

1

FAA Aircraft Certification Service SPECIAL AIRWORTHINESS INFORMATION BULLETIN http://www.faa.gov/aircraft/safety/alerts/SAIB

SAIB: SW-07-22R1 Date: April 3, 2007 This is information only. Recommendations aren’t mandatory.

Introduction

This REVISED Special Airworthiness Information Bulletin (SAIB) updates and further clarifies information issued in SAIB SW-07-22 on March 22, 2007. We’ve used “revision marks” in this SAIB to notate these updates.

This SAIB alerts owners and operators of all Eurocopter France (ECF) AS350 Astar and AS355E Twinstar helicopters to a potential flight safety hazard concerning the serrated lock washers (part number 341A75-3000-20) on the lower servo-control rod end-fittings on flight control actuators. (See Figure 2) (P/N 341A75-3000-20 is identified in the Illustrated Parts Catalog (IPC) as “Lock Nut”)

The target audience for this SAIB is the MAINTENANCE AND PILOT community for Eurocopter products.

Background

We have become aware of the potential for separation of, or excessive wear on, the inner tang of the serrated lock washer, P/N 341A75-3000-20 located on the servo control lower rod end-fittings. This condition, if proper torque is not applied to the jam nut, could lead to flight control disconnect and subsequent loss of aircraft control.

Eurocopter issued a Telex (T.F.S. No. 00000382) dated 28 March 2007 for all AS350 and AS355E models concerning this issue. This update supersedes TELEX INFORMATION No. TFS 00000379, issued on March 20, 2007.

Recommendations

We strongly recommend that mechanics and pilots of Eurocopter AS350 Astar and AS355E Twinstar helicopters perform the following actions:

Maintenance Actions:

• Immediately inspect the nut (jam nut), serrated lock washer and lock-wire on the lower servo-control rod end-fittings for condition, security and appropriate measurement, as defined in the maintenance manual. Upon next disassembly interval, inspect the serrated lock washer. If the inner tang appears worn, remove, discard, and replace with a new serrated lock washer. See Figures 1 and 2 for areas of concern; Picture 3 shows an example of a new serrated lock washer.

• When appropriate torque is applied, hardware should be torque striped to ensure unintended movement is easily identifiable.

2

• Ensure the proper torque (178 – 199 in/lbs or 2 -2.25 daN.m) and measurements, as defined in the maintenance manual, of the lower servo-control rod end-fitting jam nut. Ensure the torque points are applied as prescribed by the maintenance manual.

DO NOT use the lower servo-control rod end-fitting as a wrench attach point for torque application.

• Operators are requested to report servo-control lower rod end-fitting movement identified in this inspection and/or missing tangs or excessive wear on the inner tang serrated lock washer at the next disassembly to the point of contact (POC) listed on this SAIB.

Pilot Actions:

• Pilots should inspect the condition and security of the flight control system including the lower servo-control rod end-fitting during pre-flight inspection, if torque striped, look for misalignment. Immediately report any misalignment or other abnormal condition/security to maintenance personnel.

Figure 1

Figure 2 Flight Control Servo Actuators

Exploded View of Lower Servo Control-Rod

Servo-control rod end-fitting serrated lock washer (Lock Nut) Servo-control rod end-fitting Servo-control rod end- fitting jam nut

3

Picture 3 Example of New Serrated lock washer

For Further Information Contact: Mr. Michael Hemann, FAA Rotorcraft Directorate, ASW-112 Standards Staff, Fort Worth, Texas 76193-0110; phone: (817) 222-5336; fax: (817) 222-5961; email: [email protected]

For Related Service Information Contact: American Eurocopter Corporation, 2701 Forum Drive, Grand Prairie, Texas 75053-4005; phone: (972) 641-3460, fax: (972) 641-3527.