Taxi without clearance. Call sign similarity and communication confusion. Reporter states there were...

Narrative:

Turned up north cargo pad. Tuned ATIS and copied while taxiing forward to release spotter. Did not have letter identify so after setting altimeter, etc, listened again to get identify. Called clearance and copied. Have runway on sheet along with ATIS and clearance and thought I received taxi clearance. Background information, 121.7 listed on airport diagram as ground for west side 121.9 as ground forecast however, approach plates now show 121.9 as ground. Early am and late pm the controller talks over both ground and both tower frequencys. So you can hear his broadcast on all frequencys but only aircraft on the one you have dialed in. I was on 121.7 and believe I called and received clearance and taxied my call sign xyza, call sign xyzb and xyzc, turn up and taxi at same time, xyzc was already up and on taxiway B, xyzb was to my left on 121.9. As I said previously I thought I had received taxi permission and read back. No counter from ground so I was taxiing to runway 5L via taxiway B. Xyzc took taxiway C intersection departure. I called ground for a taxiway B4 intersection as air carrier X jet was holding on taxiway B well short (sometimes takeoff delay for time clearance). Called ground no answer. Frequency 121.7 adjusted volume and called again. They said was that xyzb? I said no sir, xyza, some confusion to identify, but I thought due to different frequencys I might have stepped on xyzb. Called again and seemed to be some sorting out of 'who's on first?' voice change and controller said taxiway B4 would be a 3 min wake turbulence delay for departing jet air carrier X now moving, said I would continue for full length. Got in vicinity of hold short, switched tower 127.45 called for departure runway 5L. Controller said was that xyza? I said affirmative. Call sign xyza for runway 5L. He then cleared call sign xyza, cleared position and hold. I've been rolling this over in my mind and then unusual radio conversation sorting out who's on first as I taxied down taxiway B and then the overly cautious, to make sure I had it right, clearance to position and hold and then takeoff led me to believe I might have messed up. The side tone on air carrier X, call sign xyza that day, because of built in intercom system sometimes leads one to think a call has gone out when the keying of the radio is not complete. The full cargo C208's that don't have intercom system, if you didn't hear it no one else did. Also the different frequencys 121.9 and 121.7 where we hear controller and not other aircraft. I might have heard call sign xyzb clearance and read back, getting stepped on or not going out, that I took his clearance. Nothing was said differently by controllers but the one who was on first left it to me that if there was a screw up it was me. From now on I'll use 121.9 for everything and possibly it should be dropped from airport diagram as it is no longer on approach plates (since air carrier X pulled out) and use only as assigned. I hope this is all only a misconception on my part as it scares me to think I might have taxied without clearance. We've had problems in the past with our call signs, xyza, xyzb, xyzc, and reading back and occasional stepping on one another but never anything more than that. But it's really made me doubt whether or not I was in the right wed am.

Original NASA ASRS Text

Title: TAXI WITHOUT CLRNC. CALL SIGN SIMILARITY AND COM CONFUSION. RPTR STATES THERE WERE 3 ACFT WITH SIMILAR CALL SIGNS AND HE MAY HAVE THOUGHT ANOTHER ACFT CLRNC WAS FOR HIM.

Narrative: TURNED UP N CARGO PAD. TUNED ATIS AND COPIED WHILE TAXIING FORWARD TO RELEASE SPOTTER. DID NOT HAVE LETTER IDENT SO AFTER SETTING ALTIMETER, ETC, LISTENED AGAIN TO GET IDENT. CALLED CLRNC AND COPIED. HAVE RWY ON SHEET ALONG WITH ATIS AND CLRNC AND THOUGHT I RECEIVED TAXI CLRNC. BACKGROUND INFO, 121.7 LISTED ON ARPT DIAGRAM AS GND FOR W SIDE 121.9 AS GND FORECAST HOWEVER, APCH PLATES NOW SHOW 121.9 AS GND. EARLY AM AND LATE PM THE CTLR TALKS OVER BOTH GND AND BOTH TWR FREQS. SO YOU CAN HEAR HIS BROADCAST ON ALL FREQS BUT ONLY ACFT ON THE ONE YOU HAVE DIALED IN. I WAS ON 121.7 AND BELIEVE I CALLED AND RECEIVED CLRNC AND TAXIED MY CALL SIGN XYZA, CALL SIGN XYZB AND XYZC, TURN UP AND TAXI AT SAME TIME, XYZC WAS ALREADY UP AND ON TXWY B, XYZB WAS TO MY L ON 121.9. AS I SAID PREVIOUSLY I THOUGHT I HAD RECEIVED TAXI PERMISSION AND READ BACK. NO COUNTER FROM GND SO I WAS TAXIING TO RWY 5L VIA TXWY B. XYZC TOOK TXWY C INTXN DEP. I CALLED GND FOR A TXWY B4 INTXN AS ACR X JET WAS HOLDING ON TXWY B WELL SHORT (SOMETIMES TKOF DELAY FOR TIME CLRNC). CALLED GND NO ANSWER. FREQ 121.7 ADJUSTED VOLUME AND CALLED AGAIN. THEY SAID WAS THAT XYZB? I SAID NO SIR, XYZA, SOME CONFUSION TO IDENT, BUT I THOUGHT DUE TO DIFFERENT FREQS I MIGHT HAVE STEPPED ON XYZB. CALLED AGAIN AND SEEMED TO BE SOME SORTING OUT OF 'WHO'S ON FIRST?' VOICE CHANGE AND CTLR SAID TXWY B4 WOULD BE A 3 MIN WAKE TURB DELAY FOR DEPARTING JET ACR X NOW MOVING, SAID I WOULD CONTINUE FOR FULL LENGTH. GOT IN VICINITY OF HOLD SHORT, SWITCHED TWR 127.45 CALLED FOR DEP RWY 5L. CTLR SAID WAS THAT XYZA? I SAID AFFIRMATIVE. CALL SIGN XYZA FOR RWY 5L. HE THEN CLRED CALL SIGN XYZA, CLRED POS AND HOLD. I'VE BEEN ROLLING THIS OVER IN MY MIND AND THEN UNUSUAL RADIO CONVERSATION SORTING OUT WHO'S ON FIRST AS I TAXIED DOWN TXWY B AND THEN THE OVERLY CAUTIOUS, TO MAKE SURE I HAD IT RIGHT, CLRNC TO POS AND HOLD AND THEN TKOF LED ME TO BELIEVE I MIGHT HAVE MESSED UP. THE SIDE TONE ON ACR X, CALL SIGN XYZA THAT DAY, BECAUSE OF BUILT IN INTERCOM SYS SOMETIMES LEADS ONE TO THINK A CALL HAS GONE OUT WHEN THE KEYING OF THE RADIO IS NOT COMPLETE. THE FULL CARGO C208'S THAT DON'T HAVE INTERCOM SYS, IF YOU DIDN'T HEAR IT NO ONE ELSE DID. ALSO THE DIFFERENT FREQS 121.9 AND 121.7 WHERE WE HEAR CTLR AND NOT OTHER ACFT. I MIGHT HAVE HEARD CALL SIGN XYZB CLRNC AND READ BACK, GETTING STEPPED ON OR NOT GOING OUT, THAT I TOOK HIS CLRNC. NOTHING WAS SAID DIFFERENTLY BY CTLRS BUT THE ONE WHO WAS ON FIRST LEFT IT TO ME THAT IF THERE WAS A SCREW UP IT WAS ME. FROM NOW ON I'LL USE 121.9 FOR EVERYTHING AND POSSIBLY IT SHOULD BE DROPPED FROM ARPT DIAGRAM AS IT IS NO LONGER ON APCH PLATES (SINCE ACR X PULLED OUT) AND USE ONLY AS ASSIGNED. I HOPE THIS IS ALL ONLY A MISCONCEPTION ON MY PART AS IT SCARES ME TO THINK I MIGHT HAVE TAXIED WITHOUT CLRNC. WE'VE HAD PROBS IN THE PAST WITH OUR CALL SIGNS, XYZA, XYZB, XYZC, AND READING BACK AND OCCASIONAL STEPPING ON ONE ANOTHER BUT NEVER ANYTHING MORE THAN THAT. BUT IT'S REALLY MADE ME DOUBT WHETHER OR NOT I WAS IN THE RIGHT WED AM.

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.

Attributes
ACN	339850
Time
Date	199606
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : rdu
State Reference	NC
Altitude	agl bound lower : 0 agl bound upper : 0
Environment
Light	Dawn
Aircraft 1
Operator	common carrier : air taxi
Make Model Name	Caravan 1 208A
Operating Under FAR Part	Part 135
Flight Phase	ground other : taxi
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : private pilot : atp
Experience	flight time last 90 days : 60 flight time total : 6500 flight time type : 1200
ASRS Report	339850
Person 2
Affiliation	government : faa
Function	controller : ground
Qualification	controller : non radar
Events
Anomaly	non adherence : clearance other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : detected after the fact
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Taxi without clearance. Call sign similarity and communication confusion. Reporter states there were 3 aircraft with similar call signs and he may have thought another aircraft clearance was for him.