Narrative:

After doing some air work in a block of airspace northeast of grand forks international airport, we called approach with a request for vectors to the VOR runway 17R full stop. I was the PIC with an instrument flight instructor applicant in the right seat. He was 'teaching' me the approach. We were starting to pick up the VOR needle and approach advised us to expect a vector through the final approach course. We replied, 'roger.' right when the needle was centered, approach gave us an approach clearance. 'Aircraft xyz, turn left heading 200 degrees, descend and maintain 2600 ft until established, cleared VOR runway 17R approach.' we read back the clearance, '200 degrees, 2600 ft until established, cleared for the approach, aircraft xyz.' so we started our descent down to 2600 ft from 4000 ft and turned to maintain the final approach course. Approach then told us to contact arrival on 121.1. We made the switch and called them up. After descending from our initial altitude of 4000 ft, we were now passing through 3700 ft when arrival came on and said 'aircraft xyz, you were not cleared for the approach, maintain 3700 ft, turn right 270 degrees.' I called them and said 'roger 270 degrees, 3700 ft,' and informed them that we were told by approach we wre cleared. Then it sounded like the approach controller's voice that came on the arrival frequency and said the clearance was for a similar call sign from the same flight school. We were not told to call approach when we landed. I believe the cause of this mishap to definitely be similar sounding call signs. I fly quite often around the area and when 2 call signs sound the same, approach usually advises you of the situation. It is also a training environment, with both flight students and approach students. The arrival controller appeared to be a trainee at the time. This could have also been caught when we read back the approach clearance. Approach didn't advise us that it was for xyz, not xya. I also did not hear xyz call up and verify if the clearance was for him. I honestly believe the clearance was read for us, when the approach controller mean to call aircraft xya. In the future I will definitely be more distinct with the pronunciation of my call sign so the approach controller can catch it before we make a descent or turn. I am also going to bring up, to our management, the possibility of changing our call signs to the spoken individual numbers instead of the group-wise format of numbers lumped together.

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Original NASA ASRS Text

Title: A PA28 CFI EXPERIENCED A SIMILAR SOUNDING CALL SIGN PROB AND BEGAN THE APCH TO RDR WITHOUT PERMISSION.

Narrative: AFTER DOING SOME AIR WORK IN A BLOCK OF AIRSPACE NE OF GRAND FORKS INTL ARPT, WE CALLED APCH WITH A REQUEST FOR VECTORS TO THE VOR RWY 17R FULL STOP. I WAS THE PIC WITH AN INSTRUMENT FLT INSTRUCTOR APPLICANT IN THE R SEAT. HE WAS 'TEACHING' ME THE APCH. WE WERE STARTING TO PICK UP THE VOR NEEDLE AND APCH ADVISED US TO EXPECT A VECTOR THROUGH THE FINAL APCH COURSE. WE REPLIED, 'ROGER.' RIGHT WHEN THE NEEDLE WAS CTRED, APCH GAVE US AN APCH CLRNC. 'ACFT XYZ, TURN L HDG 200 DEGS, DSND AND MAINTAIN 2600 FT UNTIL ESTABLISHED, CLRED VOR RWY 17R APCH.' WE READ BACK THE CLRNC, '200 DEGS, 2600 FT UNTIL ESTABLISHED, CLRED FOR THE APCH, ACFT XYZ.' SO WE STARTED OUR DSCNT DOWN TO 2600 FT FROM 4000 FT AND TURNED TO MAINTAIN THE FINAL APCH COURSE. APCH THEN TOLD US TO CONTACT ARR ON 121.1. WE MADE THE SWITCH AND CALLED THEM UP. AFTER DSNDING FROM OUR INITIAL ALT OF 4000 FT, WE WERE NOW PASSING THROUGH 3700 FT WHEN ARR CAME ON AND SAID 'ACFT XYZ, YOU WERE NOT CLRED FOR THE APCH, MAINTAIN 3700 FT, TURN R 270 DEGS.' I CALLED THEM AND SAID 'ROGER 270 DEGS, 3700 FT,' AND INFORMED THEM THAT WE WERE TOLD BY APCH WE WRE CLRED. THEN IT SOUNDED LIKE THE APCH CTLR'S VOICE THAT CAME ON THE ARR FREQ AND SAID THE CLRNC WAS FOR A SIMILAR CALL SIGN FROM THE SAME FLT SCHOOL. WE WERE NOT TOLD TO CALL APCH WHEN WE LANDED. I BELIEVE THE CAUSE OF THIS MISHAP TO DEFINITELY BE SIMILAR SOUNDING CALL SIGNS. I FLY QUITE OFTEN AROUND THE AREA AND WHEN 2 CALL SIGNS SOUND THE SAME, APCH USUALLY ADVISES YOU OF THE SIT. IT IS ALSO A TRAINING ENVIRONMENT, WITH BOTH FLT STUDENTS AND APCH STUDENTS. THE ARR CTLR APPEARED TO BE A TRAINEE AT THE TIME. THIS COULD HAVE ALSO BEEN CAUGHT WHEN WE READ BACK THE APCH CLRNC. APCH DIDN'T ADVISE US THAT IT WAS FOR XYZ, NOT XYA. I ALSO DID NOT HEAR XYZ CALL UP AND VERIFY IF THE CLRNC WAS FOR HIM. I HONESTLY BELIEVE THE CLRNC WAS READ FOR US, WHEN THE APCH CTLR MEAN TO CALL ACFT XYA. IN THE FUTURE I WILL DEFINITELY BE MORE DISTINCT WITH THE PRONUNCIATION OF MY CALL SIGN SO THE APCH CTLR CAN CATCH IT BEFORE WE MAKE A DSCNT OR TURN. I AM ALSO GOING TO BRING UP, TO OUR MGMNT, THE POSSIBILITY OF CHANGING OUR CALL SIGNS TO THE SPOKEN INDIVIDUAL NUMBERS INSTEAD OF THE GROUP-WISE FORMAT OF NUMBERS LUMPED TOGETHER.

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.