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37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
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A radio operator relayed a clearance for ZOA but failed to obtain a correct readback causing an operational error.
| Attributes | |
| ACN | 407072 |
| Time | |
| Date | 199803 |
| Day | Sat |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| Locale Reference | atc facility : unz |
| State Reference | GU |
| Altitude | msl bound lower : 35000 msl bound upper : 35000 |
| Environment | |
| Light | Daylight |
| Aircraft 1 | |
| Operator | common carrier : air carrier |
| Make Model Name | B747 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise other |
| Route In Use | enroute : pacific |
| Flight Plan | IFR |
| Aircraft 2 | |
| Operator | common carrier : air carrier |
| Make Model Name | B747 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | Other Other |
| Flight Phase | cruise other |
| Route In Use | enroute : pacific |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | Other |
| Function | other personnel other |
| Qualification | other other : other |
| ASRS Report | 407072 |
| Person 2 | |
| Affiliation | Other |
| Function | other personnel other oversight : supervisor |
| Qualification | other other : other |
| Events | |
| Anomaly | conflict : airborne less severe non adherence : required legal separation other anomaly |
| Independent Detector | other controllera other other : unspecified atc |
| Resolutory Action | controller : issued new clearance none taken : unable other |
| Consequence | Other |
| Miss Distance | horizontal : 99999 vertical : 0 |
| Supplementary | |
| Air Traffic Incident | Operational Error |
| Situations | |
| ATC Facility | procedure or policy : unspecified |
Narrative:
Air carrier #2 and air carrier #1 were proceeding to narita, japan, via ats route B586. Both aircraft were at FL350. Xfer estimates showed the required 10 mins longitudinal separation. The aircraft position reports for waypoint payee indicated that separation had reduced to 9 mins. Immediately, the ZOA controller issued clrncs to sfoxa for delivery to both of the aircraft which would establish adequate longitudinal separation at the next waypoint, omlet. The clearance for air carrier #1 was: 'atcc air carrier #1 to cross omlet at or after XA34, maintain mach .85 or less, issue time check.' the flight was originally estimating omlet at XA32Z. The radio operator delivered the clearance accurately, but did not obtain a proper readback. As a result, the 2 flts progressed omlet with less than the required longitudinal separation and we were charged with an operational error. The radio operator apparently had a question about the readback because he repeated the at or after time and mach speed several times to ensure that the flight crew got both of these elements of the clearance right. The problem was that the most critical part of the clearance, to progress omlet 2 mins slower than estimated, was missed by the flight crew. The flight progressed omlet at the originally estimated time of XA32Z. In reviewing the recording of the event, although a low tone can be heard at the beginning of the readback, there clearly was not enough time for the flight crew to have said the words 'cross omlet at or after' at the beginning of the readback. This was a readback/hearback error.
Original NASA ASRS Text
Title: A RADIO OPERATOR RELAYED A CLRNC FOR ZOA BUT FAILED TO OBTAIN A CORRECT READBACK CAUSING AN OPERROR.
Narrative: ACR #2 AND ACR #1 WERE PROCEEDING TO NARITA, JAPAN, VIA ATS RTE B586. BOTH ACFT WERE AT FL350. XFER ESTIMATES SHOWED THE REQUIRED 10 MINS LONGITUDINAL SEPARATION. THE ACFT POS RPTS FOR WAYPOINT PAYEE INDICATED THAT SEPARATION HAD REDUCED TO 9 MINS. IMMEDIATELY, THE ZOA CTLR ISSUED CLRNCS TO SFOXA FOR DELIVERY TO BOTH OF THE ACFT WHICH WOULD ESTABLISH ADEQUATE LONGITUDINAL SEPARATION AT THE NEXT WAYPOINT, OMLET. THE CLRNC FOR ACR #1 WAS: 'ATCC ACR #1 TO CROSS OMLET AT OR AFTER XA34, MAINTAIN MACH .85 OR LESS, ISSUE TIME CHK.' THE FLT WAS ORIGINALLY ESTIMATING OMLET AT XA32Z. THE RADIO OPERATOR DELIVERED THE CLRNC ACCURATELY, BUT DID NOT OBTAIN A PROPER READBACK. AS A RESULT, THE 2 FLTS PROGRESSED OMLET WITH LESS THAN THE REQUIRED LONGITUDINAL SEPARATION AND WE WERE CHARGED WITH AN OPERROR. THE RADIO OPERATOR APPARENTLY HAD A QUESTION ABOUT THE READBACK BECAUSE HE REPEATED THE AT OR AFTER TIME AND MACH SPD SEVERAL TIMES TO ENSURE THAT THE FLC GOT BOTH OF THESE ELEMENTS OF THE CLRNC RIGHT. THE PROB WAS THAT THE MOST CRITICAL PART OF THE CLRNC, TO PROGRESS OMLET 2 MINS SLOWER THAN ESTIMATED, WAS MISSED BY THE FLC. THE FLT PROGRESSED OMLET AT THE ORIGINALLY ESTIMATED TIME OF XA32Z. IN REVIEWING THE RECORDING OF THE EVENT, ALTHOUGH A LOW TONE CAN BE HEARD AT THE BEGINNING OF THE READBACK, THERE CLRLY WAS NOT ENOUGH TIME FOR THE FLC TO HAVE SAID THE WORDS 'CROSS OMLET AT OR AFTER' AT THE BEGINNING OF THE READBACK. THIS WAS A READBACK/HEARBACK ERROR.
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.