STUDENT PLT OF AN SMA SEL TRAINING ACFT FORGOT TO TURN ON THE XPONDER ON DEP UNDER THE TCA AND PENETRATED THE TCA DURING AIR WORK PRACTICE.

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THE PURPOSE OF THE FLT WAS TO PRACTICE STEEP TURNS; SLOW FLT AND STALLS IN PREPARATION FOR MY PRIVATE PLT FLT CHK. DURING THE BEFORE TKOF CHKLIST; I BECAME DISTRACTED BY ANOTHER ACFT WAITING BEHIND ME TO TKOF. I RUSHED THROUGH AND DID NOT TURN ON MY XPONDER AT THE 'RADIOS AND AVIONICS -- SET' ITEM. IF 'XPONDER -- ON' WERE ADDED TO MY CHKLIST; THIS MIGHT NOT HAVE HAPPENED. AFTER TKOF I HEADED W AT 2000 FT MSL TO CLR OUT TO THE 80/40 RING OF THE MCI TCA SO I COULD PRACTICE STALLS BTWN 3000-4000 FT MSL. THE SUN WAS BRIGHT AND IN MY FACE. THE HAZE SEEMED WORSE THAN 5 MI VISIBILITY AND THERE WAS A MODERATE HEADWIND. I DECIDED TO CLB TO GET OUT OF THE HAZE AS IT LOOKED CLEARER ABOVE. I DID NOT CONSIDER THE TCA IN THIS DECISION. I DON'T KNOW IF I BROKE THE 3000 FT OR 4000 FT LOWER LIMIT BUT I COULD HAVE BROKEN BOTH. I WAS DISTRACTED BY THE LOWER THAN EXPECTED VISIBILITY AND THEN FOCUSED ON DOING THE STALLS AND MAY HAVE ENTERED THE TCA WITH MY XPONDER OFF. I COULD HAVE AVOIDED THIS BY REGULARLY USING GND LANDMARKS TO VERIFY MY POS RELATIVE TO THE TCA.