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EC 120 hydraulic malfunction


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Last May, our B3's pump-drive input quill failed.  I'm not sure how the 120's system is layed-out, but the B3 has a belt driven pump-drive unit that is bolted to the hydraulic pump itself.  The drive unit has a female splined shaft that fits over the hydraulic pumps male splined shaft.   When ours was disassembled we found all the female splines of the pump-drive worn smooth.  In other words, the pump-drive shaft just spun around the hydraulic pump shaft without any traction.


To make matters worse, when the pump-drive failed, the check valve in the right cyclic servo failed to activate.  This caused a massive cyclic hardover that tried to snap roll the aircraft to the right.   This manually arrested hardover continued until the engine was shutdown after landing.


Of course, the Eurocopter Tech Rep's response was the all to typical: "never seen this before".  The servo was sent back to Eurocopter for tear-down and we've never heard another word abouti it.  Since then, I've been told that a similar failure was the suspected cause of a crash in LA a couple of years ago (ENG aircraft filming some awards show), and it maybe the culprit in another crash of a Grand Canyon tour aircraft.


In my humble opinion, Eurocopter goes to great pains to keep their proplems quiet.  This sentiment was tacitly verified by the NTSB rep that queried me after my incident.  Apparently, Eurocopter has been less than cooperative with the NTSB's investigations into the A-Stars "jack-stall" phenomenum.  Go figure!

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