I have recently replaced both my high pressure and low pressure switches in the hydraulic system for the landing gear.  These switches began to have trouble providing a positive and discrete on/off event when the hydraulic pressure reached the prescribed limits.  I began to hear strange crackling and static noises in my headset just prior to the hydraulic pump running (though it would just run for a fraction of a second to re-pressurize).  These strange sounds in my headset began to occur longer and longer prior to the pump tripping on.  I also began to notice some other odd electrical issues with the aircraft.  Finally, I began to suspect these switches were faulty are replaced both of them.  The problem went away and so did my electrical issues I experienced.

I suspect the pressures switches, as they age, begin to have difficulty providing a discrete on/off switching event and begin “bouncing”.  This “bouncing”, or intermittent contact, wreaks havoc with your electrical system.  It did not, however, show up on my voltmeter that I could discern.  I certainly wish I would have replaced these switches long before they began exhibiting this behavior.  Has anyone else had a similar experience?

BTW, the initial pressure switches provided by the aircraft were not very good (1989 vintage).  Since then, they were upgraded to a much better brand.  The ones I most recently purchased from Lancair (I’m on my third set) appear to be even better than the ones I replaced.  Only time and flight hours will tell how long they last.  I’ll be ready for them this time!

Don Gordon

Lancair 320, 1600 hours

Orlando, FL