Narrative:

I am a CFI. Myself and a cfii were flying an instrument flight plan to stockton, ca. The WX was en route IMC. We requested and were told by sierra approach to expect the ILS runway 29R approach into stockton. We were handed off to another controller and continued being vectored to the final approach course. We flew several vectors and were following a vector that would take us to the ILS intercept. The controller then unexpectedly told us we were being vectored to the VOR runway 29R approach and to turn to a heading of 270 degrees, direct the manteca VOR. This confused myself and the cfii on board, wondering why they changed the approach. Our workload increased because we were close to the final approach course for both approachs and now had to reconfigure the radios and change approach plates from the ILS to the VOR approach. We maintained our last assigned heading of 270 degrees. I wanted to query the controller about the sudden change, but the frequency was very congested and the controller sounded very busy. There wasn't a break in the frequency traffic to ask my questions to the controller, and we continued to fly heading 270 degrees, waiting for an approach clearance. I don't remember hearing if the controller cleared us to intercept the VOR approach and to proceed inbound with an approach clearance. While maintaining heading 270 degrees, the controller said we had deviated too far left of course, and our approach clearance was canceled. The controller gave us a vector to the left for another approach. While being revectored for an approach, the frequency was still busy. Twice I was able to transmit our registration number to prompt the controller with my questions about the approach, but they went unanswered. I was finally able to ask the controller if we could expect the ILS or VOR approach to runway 29R. He replied we could expect the ILS. We flew the assigned vectors and flew the ILS to a full stop landing at stockton. I'm second-guessing myself about this event. I'm pretty positive that we didn't receive a clearance to intercept and proceed inbound on the VOR approach, so we continued flying heading 270 degrees because that was our last assigned heading. We also waited for the clearance, and also wanted to ask the controller for clarification, but the frequency congestion just wouldn't allow me to transmit my questions and ask if we were clear to intercept the inbound course. Everybody's workload was high, including the controller. The CRM between myself and the cfii could have been better also.

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Original NASA ASRS Text

Title: C182 PRACTICE APCH TO SCK, MISSED ATC TURN.

Narrative: I AM A CFI. MYSELF AND A CFII WERE FLYING AN INST FLT PLAN TO STOCKTON, CA. THE WX WAS ENRTE IMC. WE REQUESTED AND WERE TOLD BY SIERRA APCH TO EXPECT THE ILS RWY 29R APCH INTO STOCKTON. WE WERE HANDED OFF TO ANOTHER CTLR AND CONTINUED BEING VECTORED TO THE FINAL APCH COURSE. WE FLEW SEVERAL VECTORS AND WERE FOLLOWING A VECTOR THAT WOULD TAKE US TO THE ILS INTERCEPT. THE CTLR THEN UNEXPECTEDLY TOLD US WE WERE BEING VECTORED TO THE VOR RWY 29R APCH AND TO TURN TO A HDG OF 270 DEGS, DIRECT THE MANTECA VOR. THIS CONFUSED MYSELF AND THE CFII ON BOARD, WONDERING WHY THEY CHANGED THE APCH. OUR WORKLOAD INCREASED BECAUSE WE WERE CLOSE TO THE FINAL APCH COURSE FOR BOTH APCHS AND NOW HAD TO RECONFIGURE THE RADIOS AND CHANGE APCH PLATES FROM THE ILS TO THE VOR APCH. WE MAINTAINED OUR LAST ASSIGNED HDG OF 270 DEGS. I WANTED TO QUERY THE CTLR ABOUT THE SUDDEN CHANGE, BUT THE FREQ WAS VERY CONGESTED AND THE CTLR SOUNDED VERY BUSY. THERE WASN'T A BREAK IN THE FREQ TFC TO ASK MY QUESTIONS TO THE CTLR, AND WE CONTINUED TO FLY HDG 270 DEGS, WAITING FOR AN APCH CLRNC. I DON'T REMEMBER HEARING IF THE CTLR CLRED US TO INTERCEPT THE VOR APCH AND TO PROCEED INBOUND WITH AN APCH CLRNC. WHILE MAINTAINING HDG 270 DEGS, THE CTLR SAID WE HAD DEVIATED TOO FAR L OF COURSE, AND OUR APCH CLRNC WAS CANCELED. THE CTLR GAVE US A VECTOR TO THE L FOR ANOTHER APCH. WHILE BEING REVECTORED FOR AN APCH, THE FREQ WAS STILL BUSY. TWICE I WAS ABLE TO XMIT OUR REGISTRATION NUMBER TO PROMPT THE CTLR WITH MY QUESTIONS ABOUT THE APCH, BUT THEY WENT UNANSWERED. I WAS FINALLY ABLE TO ASK THE CTLR IF WE COULD EXPECT THE ILS OR VOR APCH TO RWY 29R. HE REPLIED WE COULD EXPECT THE ILS. WE FLEW THE ASSIGNED VECTORS AND FLEW THE ILS TO A FULL STOP LNDG AT STOCKTON. I'M SECOND-GUESSING MYSELF ABOUT THIS EVENT. I'M PRETTY POSITIVE THAT WE DIDN'T RECEIVE A CLRNC TO INTERCEPT AND PROCEED INBOUND ON THE VOR APCH, SO WE CONTINUED FLYING HDG 270 DEGS BECAUSE THAT WAS OUR LAST ASSIGNED HDG. WE ALSO WAITED FOR THE CLRNC, AND ALSO WANTED TO ASK THE CTLR FOR CLARIFICATION, BUT THE FREQ CONGESTION JUST WOULDN'T ALLOW ME TO XMIT MY QUESTIONS AND ASK IF WE WERE CLR TO INTERCEPT THE INBOUND COURSE. EVERYBODY'S WORKLOAD WAS HIGH, INCLUDING THE CTLR. THE CRM BTWN MYSELF AND THE CFII COULD HAVE BEEN BETTER ALSO.

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.