F100 flight crew initiate TCASII descent due to converging, descending conflict S80.

Attributes
ACN	529911
Time
Date	200111
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : rst.airport
State Reference	MN
Altitude	msl single value : 20000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau.artcc
Operator	common carrier : air carrier
Make Model Name	Fokker 100
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zau.artcc
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	529911
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne critical non adherence : required legal separation
Independent Detector	aircraft equipment : tcas other flight crewa
Resolutory Action	flight crew : returned to assigned altitude flight crew : took evasive action flight crew : took precautionary avoidance action
Consequence	other
Miss Distance	horizontal : 0 vertical : 500
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

During cruise phase of flight, received a TCASII TA at 12 O'clock position, 15 mi, +600 ft descending. Shortly thereafter, TCASII RA mode commanded a descent while other aircraft continued its descent towards FL200. ATC was informed of our descent below FL200. Maneuvering all in accordance with TCASII commands. Opposing aircraft passed overhead at 500 ft separation. Type was a S80. Total descent deviation by our aircraft following TCASII to 19300 ft altitude. No further flight anomalies noted.

Original NASA ASRS Text

Title: F100 FLC INITIATE TCASII DSCNT DUE TO CONVERGING, DSNDING CONFLICT S80.

Narrative: DURING CRUISE PHASE OF FLT, RECEIVED A TCASII TA AT 12 O'CLOCK POS, 15 MI, +600 FT DSNDING. SHORTLY THEREAFTER, TCASII RA MODE COMMANDED A DSCNT WHILE OTHER ACFT CONTINUED ITS DSCNT TOWARDS FL200. ATC WAS INFORMED OF OUR DSCNT BELOW FL200. MANEUVERING ALL IN ACCORDANCE WITH TCASII COMMANDS. OPPOSING ACFT PASSED OVERHEAD AT 500 FT SEPARATION. TYPE WAS A S80. TOTAL DSCNT DEV BY OUR ACFT FOLLOWING TCASII TO 19300 FT ALT. NO FURTHER FLT ANOMALIES NOTED.

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.