Recommendations Follow Fatal Accident In 2009

The FAA has published a revised Special Airworthiness Information Bulletin (SAIB) for Cessna Models 336, 337, and F337 (Reims) series airplanes with wingtip extensions. The Administration says the revision is a result of comments received from individuals and other airworthiness authorities. It
corrects a typographical error, adds to the list of models potentially affected, and adds to the list of focused inspections.

The SAIB is based on preliminary investigation findings from a fatal accident involving a Cessna Model T337G. The airplane experienced separation of a six-foot section of the outboard right wing. This airplane had been modified with an STC for extended wingtips. It also had an additional STC for winglets. For more information on the accident, see the NTSB preliminary report ERA10FA140. The subsequent investigation revealed there have also been reports from the field of wrinkled skins, working rivets, cracks, and loose wing tips. The FAA notes that Cessna Service Newsletter SNL06-6, FAA Approved Supplemental Type Certificates (STC’s) and FAA-PMA Approved Parts, as well as Aviation Enterprises Wing Extension Service Letter AE01-11-00 have already been issued for the modification.

The FAA recommends that owners and operators of the listed aircraft:

• Review and adhere to all published airspeed and maneuvering limitations for the modified airplane. Look for excessive “bowing” of the tip extensions in flight.
• Perform a one-time general inspection of the wings for internal and external damage from Wing Station (WSTA) 23 to the wing tip within the next 100 hours time-in-service (TIS). Remove all wing access panels to conduct the inspection. Areas to focus on are listed below. Do this inspection following the appropriate manufacture’s service information and any other appropriate guidance, such as FAA Advisory Circular AC 43.13-1B Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair.

Focused inspection items to focus on:

• Wrinkles in upper wing skins.
• Cracking of the upper wing skins. Pay particular attention to any wrinkles, the radius between stiffeners at Wing Station (WSTA) 150 (under fuel tank covers), and unreinforced access holes.
• Smoking rivets at the rib near the inboard aileron hinge (WSTA 162).
• Missing fastener hardware, particularly for attachment of the tips.
• Excessive looseness of attachments of the tip extension to the wing and wing tip to wing extension when pushing up and down on the tip.
• Any signs of distress along both front and rear spars, particularly in the area around WSTA 177.
• Unusual repairs to the upper skins, particularly in the area of WSTA 150-162, and Inter-rivet buckling of the stringers attached to the upper surface skin, outboard of the fueltank access covers.

In the case of multiple STC installations on the same aircraft, the FAA says to make sure the following determination, noted on the STC certificate, has been made: "This approval should not be extended to aircraft of this model on which other previously approved modifications are incorporated unless it is determined that the interrelationship between this change and any of those other previously approved modifications will introduce no adverse effect upon the airworthiness of that aircraft."

The FAA says the investigation into this incident is ongoing, but has not determined that the condition warrants an Airworthiness Directive at this time.

FMI: www.faa.gov