Thanks for the info, I am going to have to go through all that I found again. For now, Both relays were hot, electrically and thermally when I checked it out in the hangar. We had to replace the high pressure switch before the system could be run, and also we replaced the hydraulic motor??

 

I have replaced the relays also, with the Bosch relays suggested in the SB or News.

Don,

 

Hmmmmmmmmmm...............................

 

If the high pressure switch (up) failed in the open position, you should not have had any problem although its' failure in any position, open or closed, wouldn't matter if their was no power in that part of the circuit to begin with, a relay wasn't stuck or relay contacts weren't welded!  Read on.

 

1. When the pressure is lower than that required to open the pressure switch contacts (up and stowed or down and locked), they will be closed as that is their normal position (N.C.). 

 

2. If both relays were hot, both were "powered."  Did you test the continuity across the contacts in both relays after they were removed?  Did you take apart the relays to see if one was stuck or the contacts were welded?

 

3. The switch is SPDT with bus power available at the center "Pole".  The switch is always in a position where one side or the other receives power.  I have never heard of such a switch failing such that continuity exists between the pole and both contacts - However, anything is possible?

 

4. The wires leading from the Switch --> pressure switches --> relays made contact with each other creating a cross-feed?  Vibration?  Connectors bundled together (of course this condition is now different because of component replacement) somehow "shorted" against one another?  ????

 

5. Power reached both + wires at the motor because both relays were powered or stuck and their contacts were closed.  As I said in another e-mail, I will check what happens in this case.

 

6. The transition light should have been on during the problem phase.  I am not expecting you to have noticed that during the landing phase - it is usually better to be looking outside.

 

7. The gear down-and-locked lights come on before the hydraulic pressure is high enough to open the pressure switch contacts. 

 

8. An internal short in the motor caused the problem even though post-mortem evidence indicated both relays were selected for a long time?  Why did you replace the motor?

 

9. Can this happen to anyone else?

 

Hmmmmmm...........

 

Below is the gear system wiring diagram from the 235/320/360 POH: