To: Pat Gerrard
What you said in jest about moving the command servos and causing the landing gear to drop is not beyond the realm of possibility. What you described as applied to electrical systems is called a sneak circuit and it could depending on the system design apply to a hydraulic system.
These were the types of failures I instructed the analysts at Agusta to look for. I don't know if they were ever able to find any that would be catastrophic or not but in any event, the manager of the Reliability department had all catastrophic failures removed from the FMEAs.
One of the failure modes I highlited was an internal leak of the electrical control valve causing the rotor brake to come on in flight. I suggested that the valve body incorporate a controlled leak back to return so that system pressure would not be applied to the rotor brake unless the pilot commanded it.
However, if there were an electrical sneak circuit, this could cause the application of the rotor brake when the pilot commanded another unrelated electrical unit either on or off.
This internal leak condition is what caused the Lauda Air 767 thrust reverser to come on in flight. The hydraulic actuator did not incorporate a controlled leak to return and when the pressure built up, the reverser deployed.
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The Cat
[This message has been edited by Lu Zuckerman (edited 15 December 2000).]
[This message has been edited by Lu Zuckerman (edited 15 December 2000).]