ATA 29-21, Aux Hydraulic Pump Control

Gate return for failed hydraulic system test. The #2 aux pump was stuck on.

Where to start?

We pulled the #2 aux pump RCCB, no pump. ( Main 3 phase power input.)
We pulled the #2 aux pump 28VDC control relay circuit breaker, no pump. (Control contactor coil voltage. Contactor not stuck closed.)
We un-assed the HSC from the rack, no pump. (Ground for contactor coil.)

After the HSC was re-racked..... the pump was on.

Conclusion? Bad HSC.

But wait..... you would think an rack un-assing would of let all the "trons" in the unit settle down. Obviously, things were still messed up. We pulled the HSC control breakers and let the damn thing sit for 2+ minutes (I only had it out of the rack for 30 seconds), push the breakers in..... no pump WTF??? I didn't care. After two successful hydro tests the pin came out. Gear up, see-ya.

Typical digital equipment, one misplaced 0 or 1, and all hell breaks loose. You would of thought 30 seconds without power would of done it.... not this time around.


Simplified schematic.


MD-11 ASM 29-21-00

That Hot Reboot works most of the time for us as well.