A320
Flight Crew Last 90 Days 162; Flight Crew Total 25000; Flight Crew Type 12688
Distraction; Confusion; Communication Breakdown; Training / Qualification
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Other / Unknown
Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft; Manuals; Procedure
On climbout the Standby Attitude Indicator (SAI) started making a grinding noise and became very unstable/shaky. As time went on; it became very loud and shaking worse. It had become very distracting both visually and noise wise. It was VFR to destination so I sent a message to Maintenance Control to see what they thought about pulling the overhead panel Circuit Breaker (CB) labeled NAV Stby Horizon at location F12. They said if I desired to do so; I would have to use my Emergency Authority. The First Officer and I both felt the instrument was a major distraction and useless like it was; so I elected to pull the CB. To our suprise; this action did NOT remove power from the SAI! So I left the breaker out and upon touchdown the flag dropped into the face of the SAI and it subsequently spooled down. We could find nothing in the flight manual that explained this. Upon arrival after accomplishing the checklists; I called and visited with Maintenance Control about this. It appears there is a CB in the E/E compartment labled STBT INST/BATT that controls a relay that latches the SAI to the Hot Batt Bus when the normal power source is removed. This has to be what happened in this case. I am very well aware of how important the SAI is; but I find it hard to believe we cannot remove power in a case like this. It was so bad; that I was wondering if the instrument could get hot enough to be a fire hazard.
Reporter stated that on touchdown the SAI went dead; apparently due to the squat switch indicating the A320 aircraft was on the ground and now conditions were OK to remove (shut-down) electrical power from the Hot Batt Bus to the SAI. But the inability to remove all power from the SAI under conditions he describes is still a concern; especially since the SAI got so hot. He has not had any response from his Air Carrier about his report.
Pilot reported the Standby Attitude Indicator (SAI) in an A320 making a grinding noise and becoming very hot; unstable/shaky on climbout. Pilot pulled the Overhead panel Circuit Breaker (CB) labeled NAV Stby Horizon at location F12; but that action DID NOT remove electrical power from SAI. Reporter stated another CB in E/E compartment labeled STBT INST/BATT controls a relay that latches the SAI to the Hot Batt bus when the normal power source is removed.