An amended clearance issued by a ZID ARTCC radar controller is misinterped by an air carrier crew resulting in a loss of separation. The controller missed the incorrect readback.

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Attributes
ACN	636582
Time
Date	200411
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : vhp.vortac
State Reference	IN
Altitude	msl bound lower : 28000 msl bound upper : 29000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude descent : vacating altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zid.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 10
ASRS Report	636582
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller time certified in position1 : 4
ASRS Report	636778
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : required legal separation non adherence : published procedure non adherence : clearance
Independent Detector	atc equipment : conflict alert other controllera other controllerb
Resolutory Action	none taken : detected after the fact
Consequence	faa : investigated
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X was issued descent to FL270, correction FL290, no delay to FL290. Air carrier X read back 'descend to FL220, no delay through FL290.' I missed the readback. Supplemental information from acn 636778: air carrier Y at FL280 switched to 133.42. Air carrier X descended to FL270. Correction FL290, no delay to FL290. Air carrier X read back FL270, no delay through FL290.

Original NASA ASRS Text

Title: AN AMENDED CLRNC ISSUED BY A ZID ARTCC RADAR CTLR IS MISINTERPED BY AN ACR CREW RESULTING IN A LOSS OF SEPARATION. THE CTLR MISSED THE INCORRECT READBACK.

Narrative: ACR X WAS ISSUED DSCNT TO FL270, CORRECTION FL290, NO DELAY TO FL290. ACR X READ BACK 'DSND TO FL220, NO DELAY THROUGH FL290.' I MISSED THE READBACK. SUPPLEMENTAL INFO FROM ACN 636778: ACR Y AT FL280 SWITCHED TO 133.42. ACR X DSNDED TO FL270. CORRECTION FL290, NO DELAY TO FL290. ACR X READ BACK FL270, NO DELAY THROUGH FL290.

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.