MD900 Main Rotor Blade Retention Bolt Check

FAA Aircraft Certification Service SPECIAL AIRWORTHINESS INFORMATION BULLETIN SUBJ: MD900 Main Rotor Blade Retention Bolt Check SAIB: SW-08-05 Date: November 14, 2007 This is information only. Recommendations aren’t mandatory.

Introduction

This Special Airworthiness Information Bulletin (SAIB) advises you, owners, and operators of McDonnell Douglas Helicopters Inc.(MDHI) model MD900 helicopters to follow certain practices when performing the required daily preflight inspections of the main rotor blade (MRB) retention bolts.

Background

Nine MDHI Model MD900 MRB retention bolts, part number 900R3100001-103, have developed fatigue cracks which propagated and severed the bolt. The cracked bolts were retained during flight and provided normal retention and control of the main rotor blade. The cracked bolts were detected during preflight inspections, during maintenance or as a result of moderate increases in aircraft vibration during flight. The cause of the fatigue crack initiation is under investigation.

Recommendations

Although a cracked MRB retention bolt is retained by the blade centrifugal loads and by the bolt retainer clip, experience has shown that a cracked bolt will migrate upward slightly with aircraft usage. The MD900 Rotorcraft Flight Manual (RFM) requires a visual check of the MRB retention bolts during the helicopter daily preflight inspection. MDHI has issued service letter SL900-056 which provides additional guidance regarding the procedures to follow when doing a visual check of the MRB retention bolts (www.mdhelicopters.com). We recommend doing a visual check of the main rotor retention bolts before or after each flight with particular care taken to check for upward migration of the MRB retention bolt head. We also recommend following the guidance of MDHI service letter SL900-056 when doing the visual check of the MRB retention bolts as required by the MD900 RFM. We request that operators and maintenance facilities inform the Los Angeles Aircraft Certification Office of any MRB bolt service difficulties.

For Further Information, Contact

Roger Durbin, Aerospace Engineer, Los Angeles Aircraft Certification Office, ANM-120L 3960 Paramount Blvd, Lakewood CA 90712 Telephone (562) 627-5233, fax: (562) 627-5210 Email: [email protected]