On August 12, 1986, a Hiller UH21E (registration N169HA) was involved in an aviation accident near Salinas, CA. Investigators recorded the probable cause as: The upper housing oil orifice was completely blocked with a foreign material containing significant quantities of silicon, resulting in oil starvation to the secondary planet system. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During cruise flight at 75-100 feet AGL, a helicopter experienced a rightward ratcheting and decrease in rotor RPM. The pilot performed an autorotation but could not cushion the landing due to low altitude and insufficient rotor RPM, resulting in a hard impact and cartwheel. Post-accident examination revealed a blocked oil orifice containing silicon, leading to oil starvation.
Accident Sequence
During a cruise flight at an altitude between 75 and 100 feet above ground level, the pilot experienced a ratcheting sensation to the right and a decrease in rotor RPM. The pilot initiated an autorotation in response to the loss of rotor RPM. However, due to the low altitude and insufficient rotor RPM, the pilot was unable to cushion the landing. The helicopter subsequently impacted the ground with significant force and cartwheeled.
Investigation Findings
A post-accident examination of the helicopter was conducted. The examination revealed that the upper housing oil orifice was completely blocked by a foreign material. This blockage resulted in oil starvation to the secondary planet system. The foreign material was analyzed and found to contain significant quantities of silicon.
Probable cause
The upper housing oil orifice was completely blocked with a foreign material containing significant quantities of silicon, resulting in oil starvation to the secondary planet system.
Frequently asked questions
What happened in the 12 Aug 1986 Hiller UH21E accident near Salinas, CA?
During cruise flight at 75-100 feet AGL, a helicopter experienced a rightward ratcheting and decrease in rotor RPM. The pilot performed an autorotation but could not cushion the landing due to low altitude and insufficient rotor RPM, resulting in a hard impact and cartwheel. Post-accident examination revealed a…
What aircraft was involved and where did it happen?
The accident on 12 Aug 1986 involved a Hiller UH21E, registration N169HA, at Salinas, CA.
What was the probable cause of the accident?
The upper housing oil orifice was completely blocked with a foreign material containing significant quantities of silicon, resulting in oil starvation to the secondary planet system.
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