Narrative:

I was administering OJT cross training at idli/psx sectors. During this time small transport X at 17000 ft was en route sat ela lisse lisse 2 hou, and small transport Y was en route erv ela lisse lisse 2 hou at 9000 ft. Small transport Y was assigned 7000 ft and was level at 7000 ft. When small transport X was issued cross lisse at and maintain 9000 ft, aircraft read back 9000 ft. Then OJT trnee cleared him direct lisse lisse 2 to shorten his route. Aircraft read back direct lisse lisse 2, 'we'll be there at 7.' neither myself nor trnee heard pilot read back 7000 ft, and at no time did we issued 7000 ft to small transport X. Small transport X was issued correct altitude and read back correct altitude, then reported leaving 17000 ft for 9000 ft. Small transport X changed altitude himself after we reclred aircraft direct lisse.

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Original NASA ASRS Text

Title: ACFT DESCENDED TO ALT OCCUPIED BY ANOTHER ACFT.

Narrative: I WAS ADMINISTERING OJT CROSS TRNING AT IDLI/PSX SECTORS. DURING THIS TIME SMT X AT 17000 FT WAS ENRTE SAT ELA LISSE LISSE 2 HOU, AND SMT Y WAS ENRTE ERV ELA LISSE LISSE 2 HOU AT 9000 FT. SMT Y WAS ASSIGNED 7000 FT AND WAS LEVEL AT 7000 FT. WHEN SMT X WAS ISSUED CROSS LISSE AT AND MAINTAIN 9000 FT, ACFT READ BACK 9000 FT. THEN OJT TRNEE CLRED HIM DIRECT LISSE LISSE 2 TO SHORTEN HIS RTE. ACFT READ BACK DIRECT LISSE LISSE 2, 'WE'LL BE THERE AT 7.' NEITHER MYSELF NOR TRNEE HEARD PLT READ BACK 7000 FT, AND AT NO TIME DID WE ISSUED 7000 FT TO SMT X. SMT X WAS ISSUED CORRECT ALT AND READ BACK CORRECT ALT, THEN RPTED LEAVING 17000 FT FOR 9000 FT. SMT X CHANGED ALT HIMSELF AFTER WE RECLRED ACFT DIRECT LISSE.

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.