Narrative:

Problem with parallel runways that use discrete frequencys but sometimes use 1 controller broadcasting on both frequencys. Ground cleared me to taxi to A9 for a vashon departure on runway 31L. Once ready for takeoff, I contacted tower on 120.6 stating 'skylane #xyz holding short A9 ready for vashon departure.' tower came back with a takeoff clearance with my complete call sign, '#xyz cleared takeoff runway 31L, north departure.' I started rolling onto runway 31L while making my clearance call to correct tower about my vashon departure. I apparently stated 'xyz cleared takeoff runway 31R vashon departure.' tower corrected my runway clearance, I apologized and restated his clearance, and he said no problem. Departed normally using vashon departure (first time using this procedure, though land at bfi regularly). There was no other exchange with the tower during the 10 mins I remained on bfi frequency 120.6. Even though I believe the minor miscoms were properly corrected and takeoff was as approved, it felt odd. I wondered if the tower controller confused my cessna with another cessna on runway 31R. He intended to clear him for takeoff on runway 31R but used my call sign. This flight was midday when bfi tends to have dedicated controllers for each runway. However, if one controller controls both runways, then his takeoff clearance is broadcast on both 120.6 and 118.3. Therefore, I could have heard a clearance with my call sign intended for a different cessna using runway 31R. This scenario seems unlikely as taxiway A9 is very close to the tower and my large call sign numbers would have been easy to reach from the tower. However, it strikes me that the advantage of using 1 controller to work parallel runways and broadcast on 2 frequencys simultaneously comes with a risk. If the controller confuses which plane is on which runway, the takeoff clearance with your call sign is still heard regardless of which runway you are using and which frequency you have tuned. If the controller confused the plane but broadcast the clearance only for the correct runway on that runway's discrete frequency, then the plane on the other parallel using a different frequency would not hear the bogus clearance at all. Separate frequencys for parallel runways seem good. Having the tower broadcast simultaneously on both frequencys seems bad. Discrete frequencys improve safety.

Google
 

Original NASA ASRS Text

Title: C182 PLT ATTEMPTS TO CLARIFY DEP INSTRUCTIONS AFTER TKOF CLRNC, USES INCORRECT RWY, AND IS CORRECTED BY BFI TWR.

Narrative: PROB WITH PARALLEL RWYS THAT USE DISCRETE FREQS BUT SOMETIMES USE 1 CTLR BROADCASTING ON BOTH FREQS. GND CLRED ME TO TAXI TO A9 FOR A VASHON DEP ON RWY 31L. ONCE READY FOR TKOF, I CONTACTED TWR ON 120.6 STATING 'SKYLANE #XYZ HOLDING SHORT A9 READY FOR VASHON DEP.' TWR CAME BACK WITH A TKOF CLRNC WITH MY COMPLETE CALL SIGN, '#XYZ CLRED TKOF RWY 31L, N DEP.' I STARTED ROLLING ONTO RWY 31L WHILE MAKING MY CLRNC CALL TO CORRECT TWR ABOUT MY VASHON DEP. I APPARENTLY STATED 'XYZ CLRED TKOF RWY 31R VASHON DEP.' TWR CORRECTED MY RWY CLRNC, I APOLOGIZED AND RESTATED HIS CLRNC, AND HE SAID NO PROB. DEPARTED NORMALLY USING VASHON DEP (FIRST TIME USING THIS PROC, THOUGH LAND AT BFI REGULARLY). THERE WAS NO OTHER EXCHANGE WITH THE TWR DURING THE 10 MINS I REMAINED ON BFI FREQ 120.6. EVEN THOUGH I BELIEVE THE MINOR MISCOMS WERE PROPERLY CORRECTED AND TKOF WAS AS APPROVED, IT FELT ODD. I WONDERED IF THE TWR CTLR CONFUSED MY CESSNA WITH ANOTHER CESSNA ON RWY 31R. HE INTENDED TO CLR HIM FOR TKOF ON RWY 31R BUT USED MY CALL SIGN. THIS FLT WAS MIDDAY WHEN BFI TENDS TO HAVE DEDICATED CTLRS FOR EACH RWY. HOWEVER, IF ONE CTLR CTLS BOTH RWYS, THEN HIS TKOF CLRNC IS BROADCAST ON BOTH 120.6 AND 118.3. THEREFORE, I COULD HAVE HEARD A CLRNC WITH MY CALL SIGN INTENDED FOR A DIFFERENT CESSNA USING RWY 31R. THIS SCENARIO SEEMS UNLIKELY AS TXWY A9 IS VERY CLOSE TO THE TWR AND MY LARGE CALL SIGN NUMBERS WOULD HAVE BEEN EASY TO REACH FROM THE TWR. HOWEVER, IT STRIKES ME THAT THE ADVANTAGE OF USING 1 CTLR TO WORK PARALLEL RWYS AND BROADCAST ON 2 FREQS SIMULTANEOUSLY COMES WITH A RISK. IF THE CTLR CONFUSES WHICH PLANE IS ON WHICH RWY, THE TKOF CLRNC WITH YOUR CALL SIGN IS STILL HEARD REGARDLESS OF WHICH RWY YOU ARE USING AND WHICH FREQ YOU HAVE TUNED. IF THE CTLR CONFUSED THE PLANE BUT BROADCAST THE CLRNC ONLY FOR THE CORRECT RWY ON THAT RWY'S DISCRETE FREQ, THEN THE PLANE ON THE OTHER PARALLEL USING A DIFFERENT FREQ WOULD NOT HEAR THE BOGUS CLRNC AT ALL. SEPARATE FREQS FOR PARALLEL RWYS SEEM GOOD. HAVING THE TWR BROADCAST SIMULTANEOUSLY ON BOTH FREQS SEEMS BAD. DISCRETE FREQS IMPROVE SAFETY.

Data retrieved from NASA's ASRS site as of July 2007 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.