RWY INCURSION AT SNA; CA.

Narrative

THE EVENT OCCURRED AT THE CONCLUSION OF AN INST TRAINING FLT. WE HAD TAXIED CLR OF RWY 19R AT SNA ARPT AND WERE HOLDING SHORT OF RWY 19L ON TXWY H. WE HAD JUST PULLED UP SHORT; AND HAD BEEN HOLDING FOR LESS THAN 1 MIN; WAITING FOR OUR CLRNC TO CROSS THE RWY. ALSO ON TXWY H WAS A CESSNA CARDINAL IMMEDIATELY TO OUR L; HOLDING SHORT OF RWY 19R. BECAUSE OF THE CARDINAL; IT WAS DIFFICULT FOR US TO TURN OUR ACFT TO GAIN A CLR VIEW OF THE TFC LNDG AND DEPARTING ON RWY 19L. WE HEARD A RADIO CALL FROM THE TWR CTLR. WHAT WE THOUGHT HE HAD SAID WAS 'CESSNA XXX CONTINUE.' I HESITATED; UNCERTAIN; AS I WAS EXPECTING A DIFFERENT PHRASING FOR OUR XING CLRNC. MY STUDENT ACKNOWLEDGED WITH 'XXX XING RWY 19L;' AND CROSSED THE RWY. AFTER XING; WE CONTACTED GND CTL; AND TAXIED BACK TO PARKING. THE GND CTLR SAID NOTHING TO INDICATE WE HAD MADE ANY ERRORS. A PHONE CALL FROM THE TWR LATER THAT DAY REVEALED WHAT HAD ACTUALLY HAPPENED. THE RADIO CALL HAD IN FACT BEEN 'ACR XXX CONTINUE;' INTENDED FOR AN ACFT WHICH HAD JUST CHKED IN WITH THE TWR ON THE ILS. THE SIMILAR SOUNDING CALL SIGN HAD LED US TO BELIEVE THAT WE HAD BEEN CLRED TO CROSS THE RWY. AFTER MY STUDENT ACKNOWLEDGED THE RADIO CALL; THE TWR CTLR DIDN'T CALL BACK TO CORRECT OUR ERROR; PROBABLY BECAUSE OF THE SPD WITH WHICH MY STUDENT CROSSED THE RWY AND THE CONGESTION ON THE FREQ. IN ADDITION; BECAUSE OF MY SEATING POS ON THE R SIDE OF THE COCKPIT OF OUR HIGH WING ACFT; COMBINED WITH OUR POOR VIEW OF THE TFC ON RWY 19L (ON OUR L SIDE); I DIDN'T SEE THE ACFT LNDG ON RWY 19L. ACCORDING TO THE CTLR I SPOKE WITH; THIS HAD LED TO A LOSS OF SEPARATION AND A NEAR MISS OF SOME 1500 FT. THE PRIMARY CAUSE OF THE INCURSION WAS THE MISUNDERSTANDING CAUSED BY THE SIMILAR SOUNDING CALL SIGNS; AND A WILLINGNESS TO PROCEED WHILE UNCERTAIN OF THE INSTRUCTIONS RECEIVED. ADD TO IT A POOR VIEW OF THE RWY; AND THESE FACTORS WHICH BY THEMSELVES PROBABLY WON'T CAUSE AN INCIDENT; COMBINE TO CAUSE AN INCIDENT.