Air carrier X descent to occupied altitude had less than standard separation from aircraft Y. System...

Attributes
ACN	279074
Time
Date	199407
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : rqz
State Reference	AL
Altitude	msl bound lower : 25300 msl bound upper : 25300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
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 : 150 flight time total : 13300 flight time type : 1700
ASRS Report	279074
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : undershoot conflict : airborne less severe non adherence : required legal separation
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action none taken : detected after the fact
Consequence	faa : investigated
Miss Distance	horizontal : 15000 vertical : 600
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X on descent to FL240, en route to huntsville, al. Leaving FL255 we received a TA followed by an RA from aircraft Y. We began a climb as instructed by TCASII then TCASII detected another conflict and advised us to stop climb, as we were nearing a second aircraft. After the second conflict, ATC instructed us to make a 90 degree right turn. The TCASII really saved us from a midair collision. ATC's corrective action would have been way too late to avert a disaster. It seems all the aircraft involved were deviating around thunderstorms. This, I believe, overwhelmed the ATC controller, who apparently lost the 'picture' of the traffic she was handling.

Original NASA ASRS Text

Title: ACR X DSCNT TO OCCUPIED ALT HAD LTSS FROM ACFT Y. SYS ERROR.

Narrative: ACR X ON DSCNT TO FL240, ENRTE TO HUNTSVILLE, AL. LEAVING FL255 WE RECEIVED A TA FOLLOWED BY AN RA FROM ACFT Y. WE BEGAN A CLB AS INSTRUCTED BY TCASII THEN TCASII DETECTED ANOTHER CONFLICT AND ADVISED US TO STOP CLB, AS WE WERE NEARING A SECOND ACFT. AFTER THE SECOND CONFLICT, ATC INSTRUCTED US TO MAKE A 90 DEG R TURN. THE TCASII REALLY SAVED US FROM A MIDAIR COLLISION. ATC'S CORRECTIVE ACTION WOULD HAVE BEEN WAY TOO LATE TO AVERT A DISASTER. IT SEEMS ALL THE ACFT INVOLVED WERE DEVIATING AROUND TSTMS. THIS, I BELIEVE, OVERWHELMED THE ATC CTLR, WHO APPARENTLY LOST THE 'PICTURE' OF THE TFC SHE WAS HANDLING.

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.

Air carrier X descent to occupied altitude had less than standard separation from aircraft Y. System error.