Aircraft #1 was given a descent clearance to FL390. Aircraft #2 was level at FL370. Aircraft #1 continued to descend to the same altitude of aircraft #2, resulting in an operational error.

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Attributes
ACN	464030
Time
Date	200002
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : lvz.vortac
State Reference	PA
Altitude	msl single value : 41000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zob.artcc
Operator	general aviation : corporate
Make Model Name	Citation X
Operating Under FAR Part	Part 91
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zob.artcc
Operator	general aviation : corporate
Make Model Name	HS 125 Series 700
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller limited radar : 3 controller radar : 9 flight time total : 2500
ASRS Report	464030
Person 2
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne critical non adherence : required legal separation other anomaly other
Independent Detector	atc equipment : conflict alert atc equipment other atc equipment : edp other controllera other controllerb
Resolutory Action	none taken : detected after the fact
Miss Distance	horizontal : 16680 vertical : 700
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Aircraft #1 was at FL410 above aircraft #2 at FL370. ZNY asked me to descend aircraft #1 to FL350. I asked if FL390 was ok. They said yes. I descended aircraft #1 to FL390. I thought aircraft #1 had the correct clearance and switched the aircraft to new york. I called traffic for aircraft #2 just as I realized aircraft #1 was descending through FL390. ZNY called and said aircraft #1 was descending to FL370 as I did not hear the incorrect readback.

Original NASA ASRS Text

Title: ACFT #1 WAS GIVEN A DSCNT CLRNC TO FL390. ACFT #2 WAS LEVEL AT FL370. ACFT #1 CONTINUED TO DSND TO THE SAME ALT OF ACFT #2, RESULTING IN AN OPERROR.

Narrative: ACFT #1 WAS AT FL410 ABOVE ACFT #2 AT FL370. ZNY ASKED ME TO DSND ACFT #1 TO FL350. I ASKED IF FL390 WAS OK. THEY SAID YES. I DSNDED ACFT #1 TO FL390. I THOUGHT ACFT #1 HAD THE CORRECT CLRNC AND SWITCHED THE ACFT TO NEW YORK. I CALLED TFC FOR ACFT #2 JUST AS I REALIZED ACFT #1 WAS DSNDING THROUGH FL390. ZNY CALLED AND SAID ACFT #1 WAS DSNDING TO FL370 AS I DID NOT HEAR THE INCORRECT READBACK.

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.