Aircraft deviated off course and came in close proximity to a descending air carrier.

Attributes
ACN	155299
Time
Date	199008
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : atl
State Reference	GA
Altitude	msl bound lower : 5500 msl bound upper : 6000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : atl
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Small Aircraft
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 5500 flight time type : 3500
ASRS Report	155299
Person 2
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument
Events
Anomaly	conflict : airborne less severe inflight encounter : weather
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : reviewed incident with flight crew Other
Miss Distance	horizontal : 1800 vertical : 500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

During radar vectors to ILS 8L controller cleared air carrier X to 5000'. When we were descending through 5500' for 5000' the controller frantically told us to level immediately and climb back up to 6000'. We immediately added maximum power and climbed back to 6000'. The controller then explained that he had an small aircraft Y near us at 5000' that was deviating off course for WX. We never saw the small aircraft. I contribute this incident to error on the controller's part. He failed to recognize the traffic conflict until we were within 500' of the same altitude as the small aircraft. Since the controller thoroughly explained (over the radio) why he had abruptly told us to climb back to 6000', I assumed that he was admitting his error. There was no question between myself and the copilot; we had originally been cleared to 5000'. I had read back the clearance to 5000' and the altitude set in the altitude alerter was 5000'. This incident would have been prevented by a greater awareness of the controller's part.

Original NASA ASRS Text

Title: ACFT DEVIATED OFF COURSE AND CAME IN CLOSE PROX TO A DESCENDING ACR.

Narrative: DURING RADAR VECTORS TO ILS 8L CTLR CLRED ACR X TO 5000'. WHEN WE WERE DSNDING THROUGH 5500' FOR 5000' THE CTLR FRANTICALLY TOLD US TO LEVEL IMMEDIATELY AND CLB BACK UP TO 6000'. WE IMMEDIATELY ADDED MAX PWR AND CLBED BACK TO 6000'. THE CTLR THEN EXPLAINED THAT HE HAD AN SMA Y NEAR US AT 5000' THAT WAS DEVIATING OFF COURSE FOR WX. WE NEVER SAW THE SMA. I CONTRIBUTE THIS INCIDENT TO ERROR ON THE CTLR'S PART. HE FAILED TO RECOGNIZE THE TFC CONFLICT UNTIL WE WERE WITHIN 500' OF THE SAME ALT AS THE SMA. SINCE THE CTLR THOROUGHLY EXPLAINED (OVER THE RADIO) WHY HE HAD ABRUPTLY TOLD US TO CLB BACK TO 6000', I ASSUMED THAT HE WAS ADMITTING HIS ERROR. THERE WAS NO QUESTION BTWN MYSELF AND THE COPLT; WE HAD ORIGINALLY BEEN CLRED TO 5000'. I HAD READ BACK THE CLRNC TO 5000' AND THE ALT SET IN THE ALT ALERTER WAS 5000'. THIS INCIDENT WOULD HAVE BEEN PREVENTED BY A GREATER AWARENESS OF THE CTLR'S PART.

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.