Light transport descends 500 ft when an aircraft descending 1000 ft above them triggers a TCASII RA.

Attributes
ACN	242374
Time
Date	199305
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : cvg
State Reference	OH
Altitude	msl bound lower : 10500 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : cvg tower : sux
Operator	common carrier : air carrier
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Flight Phase	cruise other
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 descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 250 flight time total : 7400 flight time type : 900
ASRS Report	242374
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : took evasive action flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

In approach corridor to cvg an medium large transport was instructed by ATC to descend to 12000 ft. We were level at 11000 ft as the medium large transport descended to its assigned altitude. Our TCASII system gave an RA followed by a 1500 FPM descent. We left 11000 ft and descended to 10500 ft. The TCASII then reversed to monitor vertical speed. We informed ATC of altitude deviation after frequency congestion cleared and we had climbed back to 11000 ft. The medium large transport did not appear at any time to go below 12000 ft.

Original NASA ASRS Text

Title: LTT DSNDS 500 FT WHEN AN ACFT DSNDING 1000 FT ABOVE THEM TRIGGERS A TCASII RA.

Narrative: IN APCH CORRIDOR TO CVG AN MLG WAS INSTRUCTED BY ATC TO DSND TO 12000 FT. WE WERE LEVEL AT 11000 FT AS THE MLG DSNDED TO ITS ASSIGNED ALT. OUR TCASII SYS GAVE AN RA FOLLOWED BY A 1500 FPM DSCNT. WE LEFT 11000 FT AND DSNDED TO 10500 FT. THE TCASII THEN REVERSED TO MONITOR VERT SPD. WE INFORMED ATC OF ALTDEV AFTER FREQ CONGESTION CLRED AND WE HAD CLBED BACK TO 11000 FT. THE MLG DID NOT APPEAR AT ANY TIME TO GO BELOW 12000 FT.

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.