Narrative:

The problem arose because of confusion on the approach clearance. We were on a right downwind on a heading of 150 degrees. We had been descended to 4000 ft MSL. The controller asked if we had air carrier in sight. We said we did and the controller said to follow air carrier. We understood this to mean, to turn and follow air carrier and to follow him in the descent. We believe we read back 'cleared visual approach.' the copilot and myself both agreed that this is what the controller wanted us to accomplish. After crossing the 084 degree radial off mission bay VOR and past the radio towers we began our normal rate of descent to stay on profile. At approximately 2200 ft MSL the controller said 'xyz you're supposed to be at 4000 ft MSL.' he asked if we had the traffic at 2 O'clock and we replied that we did. He was on approach to brown field. Apparently this is the reason he wanted us at 4000 ft, because the 2 O'clock traffic was at 2600 ft on the VOR approach. When we got on the ground, I called san approach and said that we were confused by the approach clearance he gave us, and that we both thought that he also wanted us to descend. It would have been more clear to us if the controller would have said 'xyz follow air carrier and maintain 4000 ft.' the phraseology by the controller led to confusion of what he wanted us to accomplish. From the flight crew's part, if there was any question on the clearance then we should have queried the controller. In our case, both myself and the copilot understood the clearance to mean we were cleared to descend. It is a good (actually bad) example of miscom. It emphasizes the importance of standard phraseology to ensure strict compliance with ATC instructions.

Google
 

Original NASA ASRS Text

Title: ACR ON DOWNWIND FOR RWY 27 SAN. ASKED IF HAD ACR IN SIGHT AND CONFIRMED IN SIGHT. THOUGHT CLRED FOR VISUAL APCH TO FOLLOW THE INBOUND ACR. BEGAN DSCNT TO 2200 FT CTLR QUERIED AND ASKED IF WE HAD TFC AT 2 O'CLOCK LNDG AT BROWN FIELD. TFC WAS IN SIGHT. CTLR WANTED TFC TO REMAIN AT 4000 FT TILL CLR OF THE BROWN ARPT. CONFUSION ON THE CLRNC.

Narrative: THE PROB AROSE BECAUSE OF CONFUSION ON THE APCH CLRNC. WE WERE ON A R DOWNWIND ON A HDG OF 150 DEGS. WE HAD BEEN DSNDED TO 4000 FT MSL. THE CTLR ASKED IF WE HAD ACR IN SIGHT. WE SAID WE DID AND THE CTLR SAID TO FOLLOW ACR. WE UNDERSTOOD THIS TO MEAN, TO TURN AND FOLLOW ACR AND TO FOLLOW HIM IN THE DSCNT. WE BELIEVE WE READ BACK 'CLRED VISUAL APCH.' THE COPLT AND MYSELF BOTH AGREED THAT THIS IS WHAT THE CTLR WANTED US TO ACCOMPLISH. AFTER XING THE 084 DEG RADIAL OFF MISSION BAY VOR AND PAST THE RADIO TWRS WE BEGAN OUR NORMAL RATE OF DSCNT TO STAY ON PROFILE. AT APPROX 2200 FT MSL THE CTLR SAID 'XYZ YOU'RE SUPPOSED TO BE AT 4000 FT MSL.' HE ASKED IF WE HAD THE TFC AT 2 O'CLOCK AND WE REPLIED THAT WE DID. HE WAS ON APCH TO BROWN FIELD. APPARENTLY THIS IS THE REASON HE WANTED US AT 4000 FT, BECAUSE THE 2 O'CLOCK TFC WAS AT 2600 FT ON THE VOR APCH. WHEN WE GOT ON THE GND, I CALLED SAN APCH AND SAID THAT WE WERE CONFUSED BY THE APCH CLRNC HE GAVE US, AND THAT WE BOTH THOUGHT THAT HE ALSO WANTED US TO DSND. IT WOULD HAVE BEEN MORE CLR TO US IF THE CTLR WOULD HAVE SAID 'XYZ FOLLOW ACR AND MAINTAIN 4000 FT.' THE PHRASEOLOGY BY THE CTLR LED TO CONFUSION OF WHAT HE WANTED US TO ACCOMPLISH. FROM THE FLC'S PART, IF THERE WAS ANY QUESTION ON THE CLRNC THEN WE SHOULD HAVE QUERIED THE CTLR. IN OUR CASE, BOTH MYSELF AND THE COPLT UNDERSTOOD THE CLRNC TO MEAN WE WERE CLRED TO DSND. IT IS A GOOD (ACTUALLY BAD) EXAMPLE OF MISCOM. IT EMPHASIZES THE IMPORTANCE OF STANDARD PHRASEOLOGY TO ENSURE STRICT COMPLIANCE WITH ATC INSTRUCTIONS.

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.