Narrative:

We were given clearance; 'air carrier X cleared to cross runway 19L; taxi into position runway 19R.' we complied with the clearance. Once in position on runway 19R; we were given; 'air carrier X cleared for takeoff runway 19R; maintain 4000 ft on departure.' (this was a change to our clearance issued 5000 ft). At the exact moment this clearance was issued to us by sna tower; the raa system verbalized; 'on runway 19R.' both the raas voice and the tower voice were female and they both were of nearly identical cadence and modulation. Fortunately; the first officer heard the altitude change by tower. I did not. Had we both missed the clearance change and tower missed our readback; due to ATC radio congestion (which happens frequently); it could have resulted in an unsafe event after departure. I realize the raa system is new and has been put in place to enhance safety; but clearly this event demonstrates how it can adversely affect safety. It is my belief that this system should only verbalize your situation when it senses your aircraft is in a position that is in conflict with your clearance. If I am incorrectly lined up on runway 19L and the active runway is runway 19R; it should then and only then tell me that I am not in compliance. If I'm given clearance to land on runway 16R at sea and I have the runway 16R localizer tuned and I subsequently line up on runway 16L; it should verbalize 'check runway' or something similar.

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Original NASA ASRS Text

Title: A B737-700 CREW RPTS THE 'ON RWY XX' RAAS VOCAL ANNUNCIATION INTERFERED WITH A CLRNC AMENDMENT AS THE ACFT WAS ENTERING THE RWY FOR TKOF.

Narrative: WE WERE GIVEN CLRNC; 'ACR X CLRED TO CROSS RWY 19L; TAXI INTO POSITION RWY 19R.' WE COMPLIED WITH THE CLRNC. ONCE IN POSITION ON RWY 19R; WE WERE GIVEN; 'ACR X CLRED FOR TKOF RWY 19R; MAINTAIN 4000 FT ON DEP.' (THIS WAS A CHANGE TO OUR CLRNC ISSUED 5000 FT). AT THE EXACT MOMENT THIS CLRNC WAS ISSUED TO US BY SNA TOWER; THE RAA SYSTEM VERBALIZED; 'ON RWY 19R.' BOTH THE RAAS VOICE AND THE TWR VOICE WERE FEMALE AND THEY BOTH WERE OF NEARLY IDENTICAL CADENCE AND MODULATION. FORTUNATELY; THE FO HEARD THE ALT CHANGE BY TWR. I DID NOT. HAD WE BOTH MISSED THE CLRNC CHANGE AND TWR MISSED OUR READBACK; DUE TO ATC RADIO CONGESTION (WHICH HAPPENS FREQUENTLY); IT COULD HAVE RESULTED IN AN UNSAFE EVENT AFTER DEP. I REALIZE THE RAA SYSTEM IS NEW AND HAS BEEN PUT IN PLACE TO ENHANCE SAFETY; BUT CLEARLY THIS EVENT DEMONSTRATES HOW IT CAN ADVERSELY AFFECT SAFETY. IT IS MY BELIEF THAT THIS SYSTEM SHOULD ONLY VERBALIZE YOUR SITUATION WHEN IT SENSES YOUR ACFT IS IN A POSITION THAT IS IN CONFLICT WITH YOUR CLRNC. IF I AM INCORRECTLY LINED UP ON RWY 19L AND THE ACTIVE RWY IS RWY 19R; IT SHOULD THEN AND ONLY THEN TELL ME THAT I AM NOT IN COMPLIANCE. IF I'M GIVEN CLRNC TO LAND ON RWY 16R AT SEA AND I HAVE THE RWY 16R LOCALIZER TUNED AND I SUBSEQUENTLY LINE UP ON RWY 16L; IT SHOULD VERBALIZE 'CHK RWY' OR SOMETHING SIMILAR.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.