Accident
A helicopter experienced extreme in-flight vibrations at 200 feet above ground level, prompting a forced landing. During the landing, the main rotor blade impacted the tail boom, causing substantial damage to the helicopter. The pilot reported that helicopter control was "10% to nil."
Examination
Post-accident examination revealed that one of three Push-Pull Rod Assemblies, part number 28-16253-1, was corroded and had separated. Analysis at the National Transportation Safety Board's Materials Laboratory indicated that most fracture areas were on a plane nearly perpendicular to the longitudinal axis of the rod, consistent with a brittle fracture mechanism such as fatigue cracking. The operator's fleet was inspected, and four other control rods were found with corrosion. The pilot noted that there was no inspection procedure for the pitch control rod at the time, and that corrosion occurred internally, invisible from the outside.
Aftermath
Following the incident, Enstrom issued Service Directive Bulletin (SDB) No. 0096, which mandates visual inspection of control rods with part numbers 28-16253-1 and 28-16253-101 based on their time in service on specific helicopter models: F-28A, F-28C, F-28F, 280, 280C, 280F, and 280FX.