ASN Wikibase Occurrence # 35151
Last updated: 24 August 2016
This information is added by users of ASN. Neither ASN nor the Flight Safety Foundation are responsible for the completeness or correctness of this information.
If you feel this information is incomplete or incorrect, you can submit corrected information
Narrative:As the NOTAR (No Tail Rotor) helicopter entered a normal descent on downwind for landing, control was lost and the helicopter entered an uncontrollable left spin as it descended to ground impact. A stress corrosion fracture and separation of a fitting in the anti-torque system thruster control cable resulted in a fixed jet thruster nozzle setting and precluded the pilot from controlling the left yawing rotation. RFM (Rotorcraft Flight Manual) procedures provided inadequate information for the pilot to understand the anti-torque system and apply proper corrective action to minimize the effects of the stuck thruster condition. FAA and the manufacturer failed to recognize the implications and significance of a known stress corrosion cracking problem and take appropriate preventative measures in a timely manner. Maintenance diagnostic actions were inadequate to correctly diagnose a yaw control system anomaly reported by the pilot 2 days prior to this flight. The pilot's negative transfer of anti-torque failure procedures from a conventionally designed helicopter precipitated improper pilot control input in response to the fixed jet thruster nozzle condition. CAUSE: The pilot's in-flight loss of control due to the failure and separation of the forward thruster control cable telescoping sleeve ball swivel fitting, which resulted in a stuck thruster and the entry into an uncontrollable yaw/spin. Also causal was the mechanics improper maintenance actions during diagnostics to determine the cause of a yaw control anomaly in that he failed to remove an access panel over the FS113 splitter to fully and completely examine the thruster control cable. Factors in the accident were: (1) the incomplete emergency procedures/system explanations in the RFM for a stuck thruster condition; (2) the pilot's negative transfer of emergency procedures from the HH-60, which likely induced him to make incorrect inputs to throttle, collective, and the anti-torque controls during the onset of the stuck thruster condition; and (3) MDHI and the cable manufacturer's failure to expeditiously diagnose and correct the stress corrosion cracking problem in the forward thruster cable ball swivel fitting.
|Type:||McDonnell Douglas MD520N|
|Owner/operator:||San Josť Police|
|C/n / msn:|| LN032|
|Fatalities:||Fatalities: 2 / Occupants: 2|
|Airplane damage:|| Written off (damaged beyond repair)|
|Location:||San Josť, CA -
United States of America
|Departure airport:||Reid Hillview, CA (RHV)|
||Updated [Aircraft type, Cn, Operator, Location, Nature, Source]|
Number of views: 1149