Narrative:

I was giving an OJT evaluation on sector R51. The developmental was working a heavy vol of traffic with the assistance of a handoff man and d-side. Mlt X checked on at FL180 and was descended to 16000'. At the same time we had a second frequency up on the overhead speaker that was emitting static and an occasionally aircraft transmission. The readback was covered by background noise (second frequency, handoff and d-side coordination and supervisor and flow controls talking about sector). The clearance was issued a second time and aircraft was issued and frequency changeover to sector R53. About 1 min later the C/a went off between military X and air carrier Y with the 2 converging. I thought that R53 was resolving the situation, but after a few radar updates I told the supervisor to check on the situation in the other sector. I cannot believe that the readback of mlt X descending to 13000' could have been missed by the radar developmental, the handoff person, the d-side and myself west/O there being some additional factor, which could have been either the split frequency overlap, static or additional background noise. Supplemental information from acn 99420: mlt X en route to abe checked on my frequency at FL180. The aircraft was descended to 16000' and read back 13000'. Again the clearance was issued to descend to 16000'. The aircraft again read back 13000'--the readback was missed. The adjacent sector accepted the handoff believing the aircraft was descending to 16000'. Mlt X was switched to frequency 120.95, but never acknowledged the change. The receiving sector had traffic at 14000' and took evasive action with that aircraft. Mlt X had to be called 2 more times before he accepted the frequency change.

Related reports:

Google
 

Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN MLT AND ACR. OPERATIONAL ERROR.

Narrative: I WAS GIVING AN OJT EVALUATION ON SECTOR R51. THE DEVELOPMENTAL WAS WORKING A HEAVY VOL OF TFC WITH THE ASSISTANCE OF A HDOF MAN AND D-SIDE. MLT X CHKED ON AT FL180 AND WAS DSNDED TO 16000'. AT THE SAME TIME WE HAD A SECOND FREQ UP ON THE OVERHEAD SPEAKER THAT WAS EMITTING STATIC AND AN OCCASIONALLY ACFT XMISSION. THE READBACK WAS COVERED BY BACKGROUND NOISE (SECOND FREQ, HDOF AND D-SIDE COORD AND SUPVR AND FLOW CTLS TALKING ABOUT SECTOR). THE CLRNC WAS ISSUED A SECOND TIME AND ACFT WAS ISSUED AND FREQ CHANGEOVER TO SECTOR R53. ABOUT 1 MIN LATER THE C/A WENT OFF BTWN MIL X AND ACR Y WITH THE 2 CONVERGING. I THOUGHT THAT R53 WAS RESOLVING THE SITUATION, BUT AFTER A FEW RADAR UPDATES I TOLD THE SUPVR TO CHK ON THE SITUATION IN THE OTHER SECTOR. I CANNOT BELIEVE THAT THE READBACK OF MLT X DSNDING TO 13000' COULD HAVE BEEN MISSED BY THE RADAR DEVELOPMENTAL, THE HDOF PERSON, THE D-SIDE AND MYSELF W/O THERE BEING SOME ADDITIONAL FACTOR, WHICH COULD HAVE BEEN EITHER THE SPLIT FREQ OVERLAP, STATIC OR ADDITIONAL BACKGROUND NOISE. SUPPLEMENTAL INFO FROM ACN 99420: MLT X ENRTE TO ABE CHKED ON MY FREQ AT FL180. THE ACFT WAS DSNDED TO 16000' AND READ BACK 13000'. AGAIN THE CLRNC WAS ISSUED TO DSND TO 16000'. THE ACFT AGAIN READ BACK 13000'--THE READBACK WAS MISSED. THE ADJACENT SECTOR ACCEPTED THE HDOF BELIEVING THE ACFT WAS DSNDING TO 16000'. MLT X WAS SWITCHED TO FREQ 120.95, BUT NEVER ACKNOWLEDGED THE CHANGE. THE RECEIVING SECTOR HAD TFC AT 14000' AND TOOK EVASIVE ACTION WITH THAT ACFT. MLT X HAD TO BE CALLED 2 MORE TIMES BEFORE HE ACCEPTED THE FREQ CHANGE.

Data retrieved from NASA's ASRS site as of August 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.