Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
SW-08-05
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: roger.durbin@faa.gov