PLT AND INSTRUCTOR ABOARD PA44 MAKE A GAR AT HEF IN THE DC ADIZ. WHEN ADVISED TO SQUAWK XXXX PER CLOSED PATTERN ADIZ PROCS; CHANGED XPONDER CODE TO 1200 INSTEAD.

Narrative

WHILE ACTING AS THE PNF AND AS FLT INSTRUCTOR; THE FOLLOWING EVENT OCCURRED WHILE INSIDE HEF CLASS D AIRSPACE. WE WERE CLRED TO LAND RWY 34L AT MANASSAS REGIONAL ARPT. WHILE ENTERING A 2 MI L BASE FOR RWY 34L; WE WERE GIVEN 2 TA'S: 1) TFC ON THE L DOWNWIND RWY 34L DOES NOT HAVE YOU IN SIGHT; 2) TFC ON SHORT FINAL RWY 34L; RPT THEM IN SIGHT. I WAS HANDLING THE RADIOS AS THE SAFETY PLT. I RPTED BOTH TA'S IN SIGHT. ON SHORT FINAL; THE RWY WAS NOT COMPLETELY CLR FROM THE ACFT THAT LANDED BEFORE US. I ADVISED MY STUDENT TO GO AROUND. HEF IS INSIDE THE WASHINGTON ADIZ. I WAS ON AN ADIZ FLT PLAN TO HEF AND WAS SQUAWKING MY DISCRETE CODE. AS WE DID THE GAR; HEF TWR ADVISED US TO SQUAWK XXXX; I SQUAWKED 1200; AND WE MADE L TFC FOR RWY 34L. APPROX 1-2 MINS LATER; TWR STATED THEY RECEIVED A CALL FROM APCH ABOUT MY 1200 SQUAWK. HEF TWR ASKED ME TO SQUAWK XXXX. I IMMEDIATELY COMPLIED WITH NO FURTHER INCIDENT. SOLUTION: KEEP CLOSE WATCH ON 1200 SQUAWKS INSIDE THE ADIZ. ADVISE CTLRS TO ALERT ALL PLTS WHO GO AROUND TO VERIFY THE XXXX SQUAWK; ESPECIALLY AFTER THESE HIGH WORKLOAD SITS; LIKE RWY NOT SAFE GAR'S.