Narrative:

Aircraft assigned descent by center from FL370 to 180 with restriction descend at 2500 FPM or more. Crew acknowledged by readback. At approximately out of FL260 center switched flight to approach control. Aircraft told to continue descent to FL110. At about FL180 first officer saw traffic ahead on airway descending on same course and asked approach to confirm descent clearance and notified approach control of traffic in sight ahead and being overtaken. ATC confirmed descent clearance and gave the overtaken aircraft type (medium large transport). Captain altered course to the left to avoid and asked first officer to report our deviation. First officer reported we have altered course to the left maintaining heading 190 to avoid getting down on overtaken aircraft. Captain asked first officer to speak directly to overtaken aircraft and give him a visual on our position (coming abeam to his left same altitude about 2 mi). First officer did and ATC (approach) instructed our flight to return to the airway. First officer reported unable to prevent midair. Approach responded with instruction to maintain heading 190 degree for sequencing. Problem resolved. Comment: flight was aware of preceding traffic in cruise ahead and below at FL330. Was also aware of traffic behind at FL370, both types twin turbine medium large transport. Reporting air carrier received descent clearance with restriction at same time as other aircraft. It was right after en route sector change. Maintain 2500 FPM or more led us to believe it was aircraft behind given simultaneous descent and we presumed that aircraft ahead had cleared. (Comment was made that preceding aircraft must have gone to mallorca, on a different airway.)

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Original NASA ASRS Text

Title: ACR MLG DEVIATES FROM AIRWAY AS TRAFFIC SIGHTED AHEAD. POTENTIAL CONFLICT SO PIC OF ACFT X MAINTAINS VISUAL ON ACFT Y IN DESCENT. ADVISES APCH CTLR. APCH CTLR ASSIGNS HEADING FOR SEQUENCE.

Narrative: ACFT ASSIGNED DSCNT BY CENTER FROM FL370 TO 180 WITH RESTRICTION DSND AT 2500 FPM OR MORE. CREW ACKNOWLEDGED BY READBACK. AT APPROX OUT OF FL260 CENTER SWITCHED FLT TO APCH CTL. ACFT TOLD TO CONTINUE DSCNT TO FL110. AT ABOUT FL180 F/O SAW TFC AHEAD ON AIRWAY DESCENDING ON SAME COURSE AND ASKED APCH TO CONFIRM DSCNT CLRNC AND NOTIFIED APCH CTL OF TFC IN SIGHT AHEAD AND BEING OVERTAKEN. ATC CONFIRMED DSCNT CLRNC AND GAVE THE OVERTAKEN ACFT TYPE (MLG). CAPT ALTERED COURSE TO THE LEFT TO AVOID AND ASKED F/O TO REPORT OUR DEVIATION. F/O REPORTED WE HAVE ALTERED COURSE TO THE LEFT MAINTAINING HDG 190 TO AVOID GETTING DOWN ON OVERTAKEN ACFT. CAPT ASKED F/O TO SPEAK DIRECTLY TO OVERTAKEN ACFT AND GIVE HIM A VISUAL ON OUR POSITION (COMING ABEAM TO HIS LEFT SAME ALT ABOUT 2 MI). F/O DID AND ATC (APCH) INSTRUCTED OUR FLT TO RETURN TO THE AIRWAY. F/O REPORTED UNABLE TO PREVENT MIDAIR. APCH RESPONDED WITH INSTRUCTION TO MAINTAIN HDG 190 DEG FOR SEQUENCING. PROBLEM RESOLVED. COMMENT: FLT WAS AWARE OF PRECEDING TFC IN CRUISE AHEAD AND BELOW AT FL330. WAS ALSO AWARE OF TFC BEHIND AT FL370, BOTH TYPES TWIN TURBINE MLG. REPORTING ACR RECEIVED DSCNT CLRNC WITH RESTRICTION AT SAME TIME AS OTHER ACFT. IT WAS RIGHT AFTER ENRTE SECTOR CHANGE. MAINTAIN 2500 FPM OR MORE LED US TO BELIEVE IT WAS ACFT BEHIND GIVEN SIMULTANEOUS DSCNT AND WE PRESUMED THAT ACFT AHEAD HAD CLRED. (COMMENT WAS MADE THAT PRECEDING ACFT MUST HAVE GONE TO MALLORCA, ON A DIFFERENT AIRWAY.)

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.