C172 ACFT ON TRAINING FLT INADVERTENTLY HAD XPONDER CODE 7700 SET AND DIDN'T NOTICE UNTIL APCH CTLR ALERTED HIM VIA UNICOM.

Narrative

ON MAY/THU/97; I WAS GIVING INSTRUCTION IN A C172 WITH A PRIMARY; PRE-SOLO STUDENT. WHILE ON THE GND; I WAS SHOWING THE STUDENT THE USE OF THE XPONDER. IN ADDITION TO THE NORMAL VFR CODE (1200); I SET THE XPONDER TO 7500; 7600; AND 7700 RESPECTIVELY; IN ORDER TO SHOW THE PROPER EMER CODES. AFTER DISPLAYING THE 7700 CODE; I BECAME DISTRACTED AND DID NOT SET THE XPONDER BACK TO 1200. THE FOLLOWING DAY; I FLEW WITH A DIFFERENT STUDENT. WHILE ON THE GND; I REALIZED THE XPONDER WAS SET TO 7700. I THEN RECYCLED THE XPONDER BACK TO 1200 (VFR). I BELIEVE THAT THE XPONDER WAS ON LONG ENOUGH THAT IT ALERTED ATC TO THE CODE. WHILE IN THE AIR; I WAS CALLED BY UNICOM TO CHK MY XPONDER. PORTLAND ATC HAD CONTACTED THE FBO TO DETERMINE THAT I WAS THE ACFT WITH THE 7700 CODE. I BELIEVE THAT EVEN THOUGH I RESET THE XPONDER; ATC HAD ALREADY BEEN ALERTED AND THE 7700 CODE REMAINED ON THEIR SCREEN. INFLT I CONTACTED PORTLAND APCH TO CONFIRM MY XPONDER CODE. THEY INFORMED ME THAT THE CODE WAS INTERMITTENT BTWN 1200 AND 7700. THEREFORE; THE INITIAL CODE OF 7700 WAS ENOUGH TO REMAIN IN THE SYS. THE FACTORS THAT LED TO THIS PROB WERE THE INABILITY OF MYSELF TO RECOGNIZE THE 7700 CODE AND CHANGE IT TO 1200 WHILE THE XPONDER HAD NO PWR. MY ACTIONS SHOWED IMPROPER USE OF THE CHKLIST AND POOR INSTRUCTION TO MY STUDENT. ADHERING TO THE CHKLIST AND STAYING ALERT WILL PREVENT THIS OCCURRING IN THE FUTURE. I AM SORRY FOR THE INCONVENIENCE IT CAUSED.