DURING TAXI FOR TKOF; BOTH OF A CRJ900'S ENGS SIMULTANEOUSLY SHUT DOWN. AFTER APU START 'L ABORT START' AND 'R ABORT START' CAUTION MESSAGES APPEARED.

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WHILE TAXIING OUT TO RWY XX WITH THE APU TURNED OFF; AS WE TURNED ONTO TXWY WE NOTED BOTH ENGS SHUT DOWN. BOTH PWR LEVERS HAD JUST BEEN PLACED BACK TO IDLE FROM THE TURN AND XING THE RWY. I STOPPED THE AIRPLANE; APPLIED THE PARKING BRAKE. WE ADVISED ATC THAT WE WOULD NOT BE ABLE TO MOVE AND THAT OUR ENGS SHUT DOWN. WE PROCEEDED WITH THE EMER CARD DUAL ENG FAILURE. WHILE DOING THE CHKLIST AND STARTING THE EMER CHKLIST IN THE POM; I STARTED THE APU. UPON STARTING THE APU WE NOTICED A L ABORT START CAUTION MESSAGE. WE PLACED THE L THRUST LEVER TO SHUTOFF AND THE R ABORT START CAUTION MESSAGE CAME UP. WE THEN PLACED THE R THRUST LEVER TO THE SHUTOFF POS. I ADVISED DISPATCH AND MAINT CTL OF THE SITUATION AND REQUESTED A TUG TO OUR LOCATION. OPS WAS ALSO NOTIFIED ALONG WITH THE FLT ATTENDANTS AND PAX. WHILE WAITING FOR THE TUG WE PROCEEDED WITH AFTER LNDG CHK AND A SHUTDOWN CHK. WE WERE ADVISED BY CTL TO START THE ENGS; WHICH WE DID. BOTH ENGS WERE STARTED AND WE RETURNED TO THE GATE WITH A TUG IN TOW IN CASE OF ANOTHER SHUTDOWN. NO FURTHER COMPLICATIONS UPON THE ARR TO THE GATE. SUPPLEMENTAL INFO FROM ACN 783537: DURING TAXI; BOTH ENGS SHUT DOWN SIMULTANEOUSLY; AS EVIDENCED BY BLACK PFD-MFD SCREENS; AND LACK OF STEERING AND BRAKING CTL. APU HAD BEEN SHUT DOWN AFTER COMPLETION OF THE AFTER-START CHKLIST. ALTHOUGH THIS IS AN EXTREMELY RARE EVENT; HAVING THE APU RUNNING WOULD HAVE PREVENTED THE ACFT FROM VEERING OFF THE CTRLINE OF THE TXWY BY PROVIDING PWR FOR BOTH STEERING AND BRAKES. CALLBACK CONVERSATION WITH RPTR ACN 783538 REVEALED THE FOLLOWING INFO: THE REPORTER IS A CHECK AIRMAN OCCUPYING THE R SEAT DURING THIS EVENT. THE ENG CONTROL SYSTEM IS FULL FADEC AND THE FLT DATA RECORDER EXAMINATION AFTER THE EVENT REVEALED THAT THE FUEL CONTROL LEVERS INTEGRATED IN THE THRUST LEVERS WERE POSITIONED AT CUTOFF. THE CUTOFF ACTION IS ACCOMPLISHED BY PRESSING OVERRIDE TRIGGERS LOCATED AT THE FLT IDLE GATE ALLOWING A TRANSITION TO CUTOFF. HOWEVER NEITHER FLT CREW MEMBER REMEMBERS MOVING THE CONTROLS TO THE CUTOFF POSITION. THE FACT THAT THE CONDITIONS RECORDED WERE SIMULTANEOUS ABORTED STARTS MIGHT LEAD ONE TO BELIEVE THE ANOMALY WAS NOT CREW INITIATED. AS A RESULT THE ACTUAL CAUSE OF THIS EVENT IS UNKNOWN: HUMAN OR TECHNICAL.