Narrative:

Early morning flight from bur to sfo. Because of the early hour we were rted to the modesto 2 arrival instead of the big sur arrival. Intercepting the arrival from the south, we were cleared direct groan, which is on the modesto 2. I thought the controller said direct tdrow and read that back. Tdrow is on the RNAV approach to runway 28R. That is what we were expecting after the modesto 2 since it was VMC. The captain also thought the controller said tdrow (not groan). This was only a 10-15 degree heading change. After 5 mins, the controller (ZOA) queried us and told us to go direct groan. I said we were, then, confused, I asked the controller to spell the fix. When he did, we understood our error. It was early in the morning. Both the controller and I probably mumble and are hard to understand. The captain and I were expecting the FMS visual approach to sfo and were spring loaded to those fixes. The controller missed my incorrect readback. There are 2 fixes on the FMS arrival that sound like groan (tdrow and garow) especially early in the morning. An initial spelling of the fix because we were somewhat confused by the fix on our initial clearance would have prevented this deviation.

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Original NASA ASRS Text

Title: AN ACR FLC IN A B737-300 MISUNDERSTOOD A CLRNC AND PROCEEDED TOWARD THE WRONG INTXN. THE CTLR CORRECTED THEM.

Narrative: EARLY MORNING FLT FROM BUR TO SFO. BECAUSE OF THE EARLY HR WE WERE RTED TO THE MODESTO 2 ARR INSTEAD OF THE BIG SUR ARR. INTERCEPTING THE ARR FROM THE S, WE WERE CLRED DIRECT GROAN, WHICH IS ON THE MODESTO 2. I THOUGHT THE CTLR SAID DIRECT TDROW AND READ THAT BACK. TDROW IS ON THE RNAV APCH TO RWY 28R. THAT IS WHAT WE WERE EXPECTING AFTER THE MODESTO 2 SINCE IT WAS VMC. THE CAPT ALSO THOUGHT THE CTLR SAID TDROW (NOT GROAN). THIS WAS ONLY A 10-15 DEG HDG CHANGE. AFTER 5 MINS, THE CTLR (ZOA) QUERIED US AND TOLD US TO GO DIRECT GROAN. I SAID WE WERE, THEN, CONFUSED, I ASKED THE CTLR TO SPELL THE FIX. WHEN HE DID, WE UNDERSTOOD OUR ERROR. IT WAS EARLY IN THE MORNING. BOTH THE CTLR AND I PROBABLY MUMBLE AND ARE HARD TO UNDERSTAND. THE CAPT AND I WERE EXPECTING THE FMS VISUAL APCH TO SFO AND WERE SPRING LOADED TO THOSE FIXES. THE CTLR MISSED MY INCORRECT READBACK. THERE ARE 2 FIXES ON THE FMS ARR THAT SOUND LIKE GROAN (TDROW AND GAROW) ESPECIALLY EARLY IN THE MORNING. AN INITIAL SPELLING OF THE FIX BECAUSE WE WERE SOMEWHAT CONFUSED BY THE FIX ON OUR INITIAL CLRNC WOULD HAVE PREVENTED THIS DEV.

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.