Air carrier X had less than standard separation from air carrier Y. System error.

Attributes
ACN	178876
Time
Date	199105
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : pxv
State Reference	IN
Altitude	msl bound lower : 28000 msl bound upper : 28000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid tower : cos
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	climbout : intermediate altitude
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 3
ASRS Report	178876
Person 2
Affiliation	government : faa
Function	controller : flight data
Qualification	controller : radar
Events
Anomaly	conflict : airborne less severe non adherence : clearance non adherence : required legal separation non adherence : published procedure
Resolutory Action	none taken : detected after the fact
Consequence	faa : investigated
Miss Distance	horizontal : 25200 vertical : 40
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error Intra Facility Coordination Failure

Narrative:

Air carrier X called on climbing to FL270. Air carrier Y was out FL350 descending to FL280. When air carrier X called, I suggested FL280 for a final. He said, 'roger, FL280'. My radar associate questioned the readback so I asked air carrier X to verify his assigned altitude. He said 'FL279' then it was garbled, 'FL280'. I thought he said 'FL270 to expect FL280'. The radar associate heard what the pilot actually said, which was, 'FL270, then you gave us FL280'. He sat there and watched as the operational error occurred.

Original NASA ASRS Text

Title: ACR X HAD LTSS FROM ACR Y. SYS ERROR.

Narrative: ACR X CALLED ON CLBING TO FL270. ACR Y WAS OUT FL350 DSNDING TO FL280. WHEN ACR X CALLED, I SUGGESTED FL280 FOR A FINAL. HE SAID, 'ROGER, FL280'. MY RADAR ASSOCIATE QUESTIONED THE READBACK SO I ASKED ACR X TO VERIFY HIS ASSIGNED ALT. HE SAID 'FL279' THEN IT WAS GARBLED, 'FL280'. I THOUGHT HE SAID 'FL270 TO EXPECT FL280'. THE RADAR ASSOCIATE HEARD WHAT THE PLT ACTUALLY SAID, WHICH WAS, 'FL270, THEN YOU GAVE US FL280'. HE SAT THERE AND WATCHED AS THE OPERATIONAL ERROR OCCURRED.

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.