An air carrier large transport crew descended in response to a TCASII command.

Attributes
ACN	256884
Time
Date	199311
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : stl
State Reference	MO
Altitude	msl bound lower : 5400 msl bound upper : 6000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : stl
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other descent : approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	256884
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance non adherence : required legal separation other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 12000 vertical : 400
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While being vectored by stl approach and avoiding heavy rain, TCASII gave a descend command. This was followed by the flight crew descending from 6000 ft to 5400 ft. Heavy rain, congested area and workload of controller contributed to this incident. Supplemental information from acn 256972: air carrier X was being worked by feeder arrival south. At his request, because of WX, he was turned to a 350 degree heading at 6000 ft and handed off to feeder arrival north. Frequency change was accomplished. Another aircraft was on final at 6000 ft and was descended to 4500 ft to avoid conflict and aircraft on opposing downwind was also at 6000 ft and descended to 5000 ft. Air carrier X had a TCASII alert with aircraft on final and descended to 5000 ft, putting him in conflict with the aircraft on final, aircraft on downwind, plus an additional aircraft on left base.

Original NASA ASRS Text

Title: AN ACR LGT CREW DSNDED IN RESPONSE TO A TCASII COMMAND.

Narrative: WHILE BEING VECTORED BY STL APCH AND AVOIDING HVY RAIN, TCASII GAVE A DSND COMMAND. THIS WAS FOLLOWED BY THE FLC DSNDING FROM 6000 FT TO 5400 FT. HVY RAIN, CONGESTED AREA AND WORKLOAD OF CTLR CONTRIBUTED TO THIS INCIDENT. SUPPLEMENTAL INFO FROM ACN 256972: ACR X WAS BEING WORKED BY FEEDER ARR S. AT HIS REQUEST, BECAUSE OF WX, HE WAS TURNED TO A 350 DEG HDG AT 6000 FT AND HANDED OFF TO FEEDER ARR N. FREQ CHANGE WAS ACCOMPLISHED. ANOTHER ACFT WAS ON FINAL AT 6000 FT AND WAS DSNDED TO 4500 FT TO AVOID CONFLICT AND ACFT ON OPPOSING DOWNWIND WAS ALSO AT 6000 FT AND DSNDED TO 5000 FT. ACR X HAD A TCASII ALERT WITH ACFT ON FINAL AND DSNDED TO 5000 FT, PUTTING HIM IN CONFLICT WITH THE ACFT ON FINAL, ACFT ON DOWNWIND, PLUS AN ADDITIONAL ACFT ON L BASE.

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.