SMA ENTERED THE TRACY; CA; ATA WITHOUT CLRNC.

Narrative

FLYING RIGHT SEAT AS FLT INSTR; TRANSITIONING A PVT PLT TO A RETRACTABLE ACFT. AFTER 1 HR AIRWORK OVER SAN JOAQUIN VALLEY; DECIDED TO PRACTICE LNDGS AT TRACY ARPT (AN UNCONTROLLED FIELD). MONITORED UNICOM; OVERFLEW FIELD AT 1500' AGL TO OBSERVE TETRAHEDRON; WHEN VOICE ON RADIO SAID; 'TRACY TFC; CONTACT TRACY TWR ON 121.2.' 'WHAT TWR?'; MY STUDENT AND I ASKED EACH OTHER. COMPLYING; WE WERE INFORMED OF TEMPORARY TWR STAFFED BY NATL GUARD. I ASKED IF AN ATA WAS IN EFFECT; AND WAS TOLD IT WAS. I RPTED POS (WELL WITHIN ATA) AND INTENTIONS AND WAS CLRED TO LAND. SINCE TRACY WAS NOT AN INTENDED DEST; JUST A SPUR OF THE MOMENT TRNING DECISION; NEITHER STUDENT NOR INSTR HAD CHKED NOTAMS. I'VE BEEN USING THIS UNCONTROLLED FIELD FOR ALMOST 10 YRS FOR JUST SUCH ACTIVITIES; AND WAS SHOCKED TO FIND IT SUDDENLY A CTLED FIELD. NATIONAL GUARD TEMPORARY ACTIVITIES WERE UNKNOWN TO STUDENT OR INSTR. (AFTERWARDS; I CHKED NOTAMS AND SURE ENOUGH; THE INFO WAS THERE!) MIL CTLR SHOWED GOOD JUDGEMENT IN MAKING ANNOUNCEMENT OVER UNICOM FREQ. HE DIDN'T SEEM PERTURBED BY OUR APPEARANCE IN HIS AIRSPACE--I IMAGINE IT HAPPENED OFTEN. I WONDER IF ANY LCL OR ITINERANT PLTS ACTUALLY BOTHERED TO CHK NOTAMS UNDER LIKE CIRCUMSTANCES. SEEMS TO ME INSTRS HAVE 2 OPTIONS: 1) CHK NOTAMS FOR EVERY FIELD WITHIN 100 MI OF THE TRNING AREA; JUST IN CASE AN UNSCHEDULED LNDG TAKES PLACE; OR 2) DO WHAT I DID--OCCASIONALLY BUST AN ATA; AND FILE AN ASRS RPT AT THE EARLIEST OPPORTUNITY.