WEEK 5
H2F brings you the ‘helicopter mayday of the week’ with a short accident report summary. I tell you what happened. You think more about why it happened. We all learn from it. Because that’s what accident reporting is for.
TITLE
Tail rotor control failure during offshore flight .
WHAT?
During an offshore flight over the Gulf of Mexico, the helicopter experienced a sudden, uncommanded left yaw during cruise. The pilot maintained control, returned to the departure airport, and carried out a run-on landing. A post-flight inspection found that a tail rotor pitch change link had fractured.
WHERE?
The event occurred during cruise flight after departure from Houma-Terrebonne Airport, Louisiana, while en route to an offshore platform.
WHEN?
It took place on February 20, 2015, at about 07:50 local time, during daytime operations. The NTSB final report was published on November 29, 2016.
HOW?
The helicopter experienced an abrupt left yaw caused by failure of a tail rotor pitch change link. The pilot elected to return to the airport and completed a run-on landing without further damage. Investigation showed that the failed pitch change link had been overhauled shortly before the event and fractured after only 14.8 flight hours. Metallurgical examination revealed fatigue cracking associated with excessive bearing friction, which resulted from stiff bearings installed during overhaul.
CONDITIONS?
The flight was conducted in day VMC with light winds and normal visibility. Operationally, there were no adverse weather or environmental factors; instead, the event was linked to mechanical and maintenance conditions involving the tail rotor control system. The overhaul manual had recently been revised, and differences in bearing inspection procedures contributed to incorrect torque assessment during maintenance.
OUTCOME?
The pilot’s successful handling of the event and decision to immediately return to the field of departure occurred before the component could completely fail in a catastrophic manner and resulted in no injuries. The helicopter sustained substantial damage due to the failed flight control component, and the tail rotor pitch change link required replacement. The investigation led to corrective actions, including updates to maintenance procedures and inspection guidance for bearing rotational torque.
WHY?
- Fracture of the tail rotor pitch change link caused by excessive bearing rotational friction.
- Bearings installed in exceedance of maximum allowable torque during overhaul.
- Undetected fatigue cracking initiated by bending loads associated with stiff bearings.
- Inadequate control and clarity of bearing replacement and inspection procedures.
- The maintenance manual had been revised about three months before the accident with a newer version using a different method for checking bearing rotational torque compared with the earlier version. The overhaul facility followed the newer procedure, but investigation later determined that the earlier procedure reflected the correct inspection method.
REFERENCE?
National Transportation Safety Board. (2016, November 29). Aviation investigation final report: Accident number CEN15LA156 (Agusta A119 Mk II, N802SM). National Transportation Safety Board. https://data.ntsb.gov/Docket?ProjectID=90780 https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/90780/pdf
Note:
Accident reports selected from the following open source databases: US NTSB; UK AAIB; Flight Safety Foundation’s Aviation Safety Network; Australia’s ATSB. Ireland’s AAIU; Taiwan’s TTSB; France’s BEA; Spain’s CIAIAC. Germany’s BFU.
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