Narrative:

The B757 was level at FL350 heading approximately 260 degrees direct to oal VOR (80 NM east) for the el nido 4 arrival into san jose, ca. ZLC stated 'air carrier xyz, descend and maintain FL310.' the clearance was read back as 'out of FL350 for FL310, air carrier xyz.' FL310 was set into the altitude alert window by the first officer and acknowledged by the captain. FL310 was then entered into the FMC to initiate a 1000 FPM cruise descent profile. While passing approximately FL325, ZLC asked 'air carrier xyz, are you leveling at FL330?' the crew response was 'negative, our last clearance was for FL310, air carrier xyz.' ZLC, 'air carrier xyz, maintain FL330, expedite climb, advise when reaching.' crew, 'roger, we're rapidly climbing to FL330, we'll advise.' the captain quickly transitioned from a 1000 FPM descent to a 2500 FPM climb at approximately FL321. FL330 was quickly established and ZLC was advised. The controller responded by saying that he may have missed our readback. A short time later, he instructed us to contact ZOA. The controller's tone and demeanor was calm and conciliatory, seeming to indicate that no traffic conflict occurred. This event highlights 2 potential hazards that negatively impact ATC communications: 1) controllers working multiple frequencys and performing multiple tasks (ie, ground control, tower, clearance delivery, approach control). In this case it appeared that the controller may have been working more than 1 frequency. This can lead to confusion when 2 aircraft on separate frequencys transmit together to the same controller. 2) current regulations do not hold controllers accountable if a clearance is read back incorrectly. This lack of mutual responsibility reduces the effectiveness of clearance readbacks. Supplemental information from acn 474224: at the time there was moderate ATC traffic. All standard ATC and company procedures were followed. Our aircraft was non TCASII.

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Original NASA ASRS Text

Title: A B757 CARGO FLT DSNDS PAST THEIR CLRED TO ALT WHEN THE CREW MISUNDERSTANDS THE CLRNC 80 MI E OF OAL, NV.

Narrative: THE B757 WAS LEVEL AT FL350 HDG APPROX 260 DEGS DIRECT TO OAL VOR (80 NM E) FOR THE EL NIDO 4 ARR INTO SAN JOSE, CA. ZLC STATED 'ACR XYZ, DSND AND MAINTAIN FL310.' THE CLRNC WAS READ BACK AS 'OUT OF FL350 FOR FL310, ACR XYZ.' FL310 WAS SET INTO THE ALT ALERT WINDOW BY THE FO AND ACKNOWLEDGED BY THE CAPT. FL310 WAS THEN ENTERED INTO THE FMC TO INITIATE A 1000 FPM CRUISE DSCNT PROFILE. WHILE PASSING APPROX FL325, ZLC ASKED 'ACR XYZ, ARE YOU LEVELING AT FL330?' THE CREW RESPONSE WAS 'NEGATIVE, OUR LAST CLRNC WAS FOR FL310, ACR XYZ.' ZLC, 'ACR XYZ, MAINTAIN FL330, EXPEDITE CLB, ADVISE WHEN REACHING.' CREW, 'ROGER, WE'RE RAPIDLY CLBING TO FL330, WE'LL ADVISE.' THE CAPT QUICKLY TRANSITIONED FROM A 1000 FPM DSCNT TO A 2500 FPM CLB AT APPROX FL321. FL330 WAS QUICKLY ESTABLISHED AND ZLC WAS ADVISED. THE CTLR RESPONDED BY SAYING THAT HE MAY HAVE MISSED OUR READBACK. A SHORT TIME LATER, HE INSTRUCTED US TO CONTACT ZOA. THE CTLR'S TONE AND DEMEANOR WAS CALM AND CONCILIATORY, SEEMING TO INDICATE THAT NO TFC CONFLICT OCCURRED. THIS EVENT HIGHLIGHTS 2 POTENTIAL HAZARDS THAT NEGATIVELY IMPACT ATC COMS: 1) CTLRS WORKING MULTIPLE FREQS AND PERFORMING MULTIPLE TASKS (IE, GND CTL, TWR, CLRNC DELIVERY, APCH CTL). IN THIS CASE IT APPEARED THAT THE CTLR MAY HAVE BEEN WORKING MORE THAN 1 FREQ. THIS CAN LEAD TO CONFUSION WHEN 2 ACFT ON SEPARATE FREQS XMIT TOGETHER TO THE SAME CTLR. 2) CURRENT REGS DO NOT HOLD CTLRS ACCOUNTABLE IF A CLRNC IS READ BACK INCORRECTLY. THIS LACK OF MUTUAL RESPONSIBILITY REDUCES THE EFFECTIVENESS OF CLRNC READBACKS. SUPPLEMENTAL INFO FROM ACN 474224: AT THE TIME THERE WAS MODERATE ATC TFC. ALL STANDARD ATC AND COMPANY PROCS WERE FOLLOWED. OUR ACFT WAS NON TCASII.

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.