TKOF ON TXWY INSTEAD OF THE RWY AT ABQ.

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GND CTL CLRED ACFT FOR TAXI TO RWY 12 AND ASKED IF PLT WAS FAMILIAR WITH ARPT. PLT RPTED 'NO;' AT WHICH TIME CTLR ADVISED TO TAXI L AND N AROUND BUILDINGS. AFTER TAXIING A SHORT DISTANCE; CTLR ASKED DIRECTION OF INTENDED FLT; TO WHICH PLT STATED 'S.' CTLR THEN ASKED IF PLT COULD ACCEPT RWY 21. REPLY WAS 'YES' AT WHICH TIME CTLR ADVISED TO TURN AROUND AND TAXI BACK TO TXWY 'CHARLIE;' WHICH WAS DONE. AFTER TAXIING A SHORT DISTANCE; CTLR ADVISED TO DO RUN-UP AT THAT POINT AND CONTACT TWR WHEN READY. PLT OBSERVED RWY STOP LINE IMMEDIATELY TO FRONT L AT WHICH RUN-UP WAS DONE. AFTER RUN-UP; TWR WS CONTACTED AND ADVISED READY FOR TKOF; RWY 21. TWR ADVISED TO TAXI ONTO TXWY 21 AND HOLD. PLT GLANCED TO LOWER R AND SAW MARKER '21-C' (UNABLE TO REMEMBER COLOR). ACFT MADE R TURN AFTER XING HOLD LINE AND ADVISED TWR 'HOLDING 21.' SHORTLY THEREAFTER; PLT WAS CLRED FOR TKOF. AFTER PWRING UP AND LEANING FOR MAX PERFORMANCE; PLT ACKNOWLEDGED 'CLRED FOR TKOF 21.' USING ALL OF THE 'RWY' FOR TKOF; PLT WAS NOTIFIED BY THE TWR THAT HE HAD JUST DEPARTED A TXWY; WHICH WAS ACKNOWLEDGED. SHORTLY THEREAFTER; DEP ALSO ADVISED PLT THAT HE HAD DEPARTED A TXWY. COPLT STATED THAT HE HAD OBSERVED A 'YELLOW-LINE' AFTER TKOF ROLL WAS COMMENCED; BUT FELT THAT HE SHOULDN'T SAY ANYTHING AS ROLL HAD ALREADY STARTED. PLT ACCEPTS FACT THAT HE PROBABLY DID TKOF ON TXWY; BUT WONDERS WHY TWR CTLR DIDN'T OBSERVE PLACEMENT OF ACFT ON TXWY AFTER HE WAS ADVISED TO HOLD AND THEN CLRED FOR TKOF. BEING UNFAMILIAR WITH THE ARPT; PLT STILL DOESN'T KNOW WHICH TXWY WAS VIOLATED. PLT HAD ALSO REVIEWED AIM FOR RWY/TXWY MARKERS AND CONFIRMS HOLD LINE; REALIZES THAT HE SHOULD HAVE BEEN MORE OBSERVANT ON YELLOW TAXI LINE. TXWY BELIEVED TO HAVE BEEN PARALLEL FOR RWY 12; BUT UNSURE AS DIRECTIONAL GYRO WAS SET TO '210' AFTER TAXIING ONTO WHAT WAS BELIEVED TO HAVE BEEN RWY 21.