Service difficulty report · Diode · Cessna 750

Difficulty date
August 23, 2019
Submitted
September 15, 2019
Operation
Air carrier
Aircraft
N769XJ
Make and model
Cessna 750
Aircraft serial
7500269
Aircraft time
12,845 hours, 6,264 cycles
Part
Diode
Part number
S31065
Condition
Shorted
Location
J-Box
Stage of operation
CL
How discovered
O
Nature of condition
B, J, G
Precautionary procedure
H, A

As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.

What was found

DURING CLIMB OUT THROUGH FL350 FOR FL450, THE FLIGHT CREW RECEIVED A FMS SINGLE OPERATION MODE MESSAGE ON THE RIGHT FMS AND THE LEFT FMS DISPLAY WENT BLANK FOLLOWED BY THE DU 1 DISPLAY GOING BLANK, FOLLOWED BY BATT 1 OVER CURRENT MESSAGE AND THE AUTOPILOT DISENGAGING. THE LEFT SIDE AUTOMATICALLY ELECTRICALLY ISOLATED WITH THE CROSS TIE OPEN. THEN, MANY EICAS MESSAGES POSTED ALL AT ONCE, INCLUDING “A” RUDDER LIMITER FAIL AND DU 1 FAIL. THE CREW BEGAN ABNORMAL PROCEDURES, EMER BUS ON THE LEFT SIDE WAS SELECTED AND A HEAVY ELECTRICAL BURNING SMELL WAS SENSED IMMEDIATELY WITHOUT SEEING ANY SMOKE. THE EMER BUS WAS DESELECTED AND BATT 1 TURNED OFF AS THE CREW NOTICED BATT 1 WAS DISCHARGING AT -199 AMPS. WITH THE POSSIBILITY OF AN ONBOARD FIRE, THE FLIGHT CREW AGREED TO DECLARE AN EMERGENCY AND DIVERT INTO PSP. AFTER TURNING OFF BATT 1, THE BURNING ODOR STARTED TO LESSEN. THE AIRCRAFT LANDED WITH NO FURTHER INCIDENT. A HEAVY BURNT ELECTRICAL SMELL WAS NOTED COMING FROM THE BAGGAGE COMPARTMENT. MAINTENANCE FOUND DIODE IN THE LH POWER J-BOX HAD SHORTED INTERNALLY, WHICH CAUSED THE AVIONICS CONTACTOR TO OPEN; DAMAGING THE LH AVIONICS RELAY (KZ003), WIRING AND CONNECTOR. AS A RESULT OF THE SHORT, DAMAGED WIRES WERE ALSO NOTED TO THE AVIONICS MASTER SWITCH AND AFT PRESSURE BULKHEAD FEED THROUGH CONNECTOR. ALL VISIBLE AND ACCESSIBLE DAMAGED WIRING AND COMPONENTS WERE REPLACED. THE AIRCRAFT WAS FERRIED TO A MAINTENANCE FACILITY FOR FURTHER INSPECTION AND REPAIRS. ACCESS WAS GAINED, AND ADDITIONAL WIRING WAS REPLACED.

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