A CFI; MONITORING HIS SOLO STUDENT DOING TOUCH AND GOES AT BOI; WATCHED HELPLESSLY AS HIS STUDENT ENTERED RWY 28R WITHOUT PERMISSION; AFTER BECOMING FLUSTERED BY ANOTHER ACFT'S STUCK MIKE AND THE STERNNESS OF BOI TWR'S INSTRUCTIONS.

Narrative

I WAS NOT ACTUALLY IN THE ACFT. I WAS OBSERVING FROM THE FBO PARKING AREA APPROX 300 YARDS FROM THE INCIDENT. MY INFO COMES FROM: 1) VISUAL OBSERVATION; 2) TALKING WITH MY STUDENT (WHO WAS SOLOING AT THE TIME); AND 3) TALKING TO A CTLR AFTER THE INCIDENT. STUDENT AND I FLEW FROM EUL TO BOI TO ALLOW STUDENT TO PRACTICE SOLO TKOF AND LNDGS AT A CTLED FIELD. STUDENT AND I HAD FLOWN INTO BOI ON 2 PRIOR OCCASIONS AND PERFORMED TKOF/LNDG OPS WHILE DUAL; AND THE STUDENT HAD DONE WELL. STUDENT FLEW US IN TO BOI AND DROPPED ME OFF AT THE FBO. STUDENT THEN PERFORMED 2 TKOF/LNDGS ON RWY 28R WITH NO TROUBLE. ON THE 3RD LNDG; TWR ASKED HIM TO LAND ON RWY 28L; WHICH HE DID. STUDENT EXITED RWY 28L AT TXWY D; AND HELD SHORT OF RWY 28R. AT THIS POINT A 'STUCK MIKE' SIT OCCURRED WITH ANOTHER ACFT AND STUDENT WAS HAVING TROUBLE COMMUNICATING WITH THE TWR. TWR THEN SHOWED STUDENT A FLASHING GREEN LIGHT AND AS STUDENT STARTED TO TAXI; HE COULD SEE A B737 ON FINAL FOR RWY 28R; HE COULD NOT ACCURATELY JUDGE ITS DISTANCE AND BECAME CONCERNED THAT MAYBE THE LIGHT SIGNAL WAS NOT FOR HIM AND THAT HE WAS GOING TO CAUSE AN ACCIDENT. SO; HE (WISELY IN MY OPINION) STOPPED AND HELD SHORT OF RWY 28R. TWR THEN (ALSO WISELY IN MY OPINION; DUE TO LACK OF 2-WAY COMS) WAS NOT SURE OF STUDENT'S INTENTIONS SO THEY ISSUED A GAR TO THE B737. COMS WERE THEN RESTORED; AND TWR ('STERNLY' ACCORDING TO STUDENT) TOLD STUDENT TO CROSS RWY 28R AND PROCEED TO PARKING. STUDENT WAS QUITE APPREHENSIVE AT THIS POINT; AND TURNED R ONTO RWY 28R THINKING THAT IT WAS THE TXWY. HE REALIZED HIS MISTAKE AS SOON AS HE WAS LINED UP ON THE RWY; AND DECIDED IT WOULD TAKE MORE TIME TO TURN AROUND AND TAXI OFF AT TXWY D. SO; HE CONTINUED AND EXITED AT TXWY C. BY THIS TIME TWR WAS QUITE UPSET; AND STUDENT APOLOGIZED AND REPEATED THAT HE WAS A STUDENT PLT. WHEN STUDENT PARKED; HE EXPLAINED THE SIT TO ME AND I CALLED THE TWR TO TALK OVER WHAT HAD HAPPENED WITH THEM. I FEEL THAT CONTRIBUTING FACTORS WERE: STUDENT PLT INEXPERIENCE; STUCK MIKE SIT ON ARPT; LIGHT SIGNALS; PROX OF LNDG TFC. CORRECTIVE ACTIONS WILL INCLUDE ADDITIONAL INSTRUCTION ON UNUSUAL SITS (LIGHT SIGNALS; STUCK MIKE) AND OPS AT BUSY; CTLED ARPTS.