Narrative:

I was controling aircraft inbound for atl. I meant to issue descent clearance to an arriving aircraft to 11000', but misspoke the altitude and issued 10000'. The pilot read back 10000' and I did not catch my mistake. Shortly thereafter, I observed the aircraft's mode C as 10800'. I immediately issued a climb back to 11000', but the first transmission was blocked. I re-issued the climb and the pilot returned to 11000' from 10600' MSL. The aircraft violated the atl ATC tower departure sector airspace. I notified my supervisor of the incident. There was no other aircraft involved. No evasive action was required. The sector was busy, the aircraft preceding the subject aircraft had not replied to several control instructions and several calls to acknowledge. After finally responding to a call of 'do you hear me,' I had to repeat several xmissions to him again and again. Then, several things needed to be done. So, in my haste to accomplish this, I may have issued the incorrect altitude inadvertently to the wrong aircraft. We use descent to 10000' on the short side, or base leg, inbound fix, so I could have meant to issue that altitude to one of those aircraft, or at least, I was thinking of that altitude. Possibly, by requiring or letting the controller re-affirm all altitude clrncs, so the controller would concentrate on the altitude issued, such as: 'air carrier X descend and maintain one-one-thousand.' pilot: 'air carrier X descending to one-one-thousand...' controller: 'air carrier X affirmative one-one-thousand.'

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Original NASA ASRS Text

Title: ACFT WAS INADVERTENTLY ISSUED A DESCENT CLRNC TO AN ALT OCCUPIED BY ANOTHER ACFT.

Narrative: I WAS CTLING ACFT INBND FOR ATL. I MEANT TO ISSUE DSCNT CLRNC TO AN ARRIVING ACFT TO 11000', BUT MISSPOKE THE ALT AND ISSUED 10000'. THE PLT READ BACK 10000' AND I DID NOT CATCH MY MISTAKE. SHORTLY THEREAFTER, I OBSERVED THE ACFT'S MODE C AS 10800'. I IMMEDIATELY ISSUED A CLB BACK TO 11000', BUT THE FIRST XMISSION WAS BLOCKED. I RE-ISSUED THE CLB AND THE PLT RETURNED TO 11000' FROM 10600' MSL. THE ACFT VIOLATED THE ATL ATC TWR DEP SECTOR AIRSPACE. I NOTIFIED MY SUPVR OF THE INCIDENT. THERE WAS NO OTHER ACFT INVOLVED. NO EVASIVE ACTION WAS REQUIRED. THE SECTOR WAS BUSY, THE ACFT PRECEDING THE SUBJECT ACFT HAD NOT REPLIED TO SEVERAL CTL INSTRUCTIONS AND SEVERAL CALLS TO ACKNOWLEDGE. AFTER FINALLY RESPONDING TO A CALL OF 'DO YOU HEAR ME,' I HAD TO REPEAT SEVERAL XMISSIONS TO HIM AGAIN AND AGAIN. THEN, SEVERAL THINGS NEEDED TO BE DONE. SO, IN MY HASTE TO ACCOMPLISH THIS, I MAY HAVE ISSUED THE INCORRECT ALT INADVERTENTLY TO THE WRONG ACFT. WE USE DSCNT TO 10000' ON THE SHORT SIDE, OR BASE LEG, INBND FIX, SO I COULD HAVE MEANT TO ISSUE THAT ALT TO ONE OF THOSE ACFT, OR AT LEAST, I WAS THINKING OF THAT ALT. POSSIBLY, BY REQUIRING OR LETTING THE CTLR RE-AFFIRM ALL ALT CLRNCS, SO THE CTLR WOULD CONCENTRATE ON THE ALT ISSUED, SUCH AS: 'ACR X DSND AND MAINTAIN ONE-ONE-THOUSAND.' PLT: 'ACR X DSNDING TO ONE-ONE-THOUSAND...' CTLR: 'ACR X AFFIRMATIVE ONE-ONE-THOUSAND.'

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.