TCASII causes medium large transport to descend 1000 ft into the ord TCA.

Attributes
ACN	242945
Time
Date	199305
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : obk airport : ord
State Reference	IL
Altitude	msl bound lower : 9000 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	arrival other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Flight Plan	VFR
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 : 7500 flight time type : 2800
ASRS Report	242945
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 other anomaly
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 15000 vertical : 1500
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

During an arrival to ord on the pullman 2 at 10000 ft MSL and 300 KTS assigned on the northbrook 077 degree radial 020 DME. We received a TCASII TA target aircraft plus 300-400 ft, 12 O'clock, 6-7 NM. The TA was followed by an RA target aircraft 12 O'clock, 5-6 NM plus 300-400 ft./ we immediately initiated a descent (RA given descend, descend) of 2000 FPM. At 9000 ft MSL we were given a clear of conflict advisory. Prior to this the first officer told ATC of our deviation. ATC apologized for missing the VFR traffic and told us to continue our descent to 8000 ft. We continued descending to 8000 ft and were still at 300 KTS. Once at 8000 ft and established on arrival, we slowed.

Original NASA ASRS Text

Title: TCASII CAUSES MLG TO DSND 1000 FT INTO THE ORD TCA.

Narrative: DURING AN ARR TO ORD ON THE PULLMAN 2 AT 10000 FT MSL AND 300 KTS ASSIGNED ON THE NORTHBROOK 077 DEG RADIAL 020 DME. WE RECEIVED A TCASII TA TARGET ACFT PLUS 300-400 FT, 12 O'CLOCK, 6-7 NM. THE TA WAS FOLLOWED BY AN RA TARGET ACFT 12 O'CLOCK, 5-6 NM PLUS 300-400 FT./ WE IMMEDIATELY INITIATED A DSCNT (RA GIVEN DSND, DSND) OF 2000 FPM. AT 9000 FT MSL WE WERE GIVEN A CLR OF CONFLICT ADVISORY. PRIOR TO THIS THE FO TOLD ATC OF OUR DEV. ATC APOLOGIZED FOR MISSING THE VFR TFC AND TOLD US TO CONTINUE OUR DSCNT TO 8000 FT. WE CONTINUED DSNDING TO 8000 FT AND WERE STILL AT 300 KTS. ONCE AT 8000 FT AND ESTABLISHED ON ARR, WE SLOWED.

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.