Altitude deviation altitude excursion after TCASII RA.

Attributes
ACN	227900
Time
Date	199212
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 5000 msl bound upper : 5800
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 175 flight time total : 2350 flight time type : 590
ASRS Report	227900
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 160 flight time total : 5400 flight time type : 4100
ASRS Report	227897
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course flight crew : took evasive action
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

We were on a downwind leg for an ILS 27L at ord. Our altitude was 5000 ft MSL and flight conditions were IMC due to an overcast cloud layer from 2500 to 6000 MSL. The TCASII display showed us 5 mi in trail of another aircraft and numerous aircraft on parallel approachs to ILS 27R at ord. I was flying and the captain worked the radios with ord approach. The controller gave us a left turn to a heading of 360 degrees. Once we were leveled out on that heading the TCASII issued an RA to climb at 1200-1500 FPM and indicated a target minus 300 ft climbing. Due to the IMC conditions and our companies rules I commenced a climb at 1500 FPM. The captain told ord approach of the RA and our climb. Ord approach told us to ignore the RA and stated other air carrier traffic 2000 ft above us. The RA continued until we reached 5800 ft MSL and at one point indicated the target as minus 100 ft climbing. Once the TCASII issued 'clear of conflict' we descended immediately back down to 5000 ft MLS. The whole event took less than 1 min and we (nor the approach controller) never saw the intruder. We suspect a TCASII system error. A normal approach and landing at ord was completed.

Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION AFTER TCASII RA.

Narrative: WE WERE ON A DOWNWIND LEG FOR AN ILS 27L AT ORD. OUR ALT WAS 5000 FT MSL AND FLT CONDITIONS WERE IMC DUE TO AN OVCST CLOUD LAYER FROM 2500 TO 6000 MSL. THE TCASII DISPLAY SHOWED US 5 MI IN TRAIL OF ANOTHER ACFT AND NUMEROUS ACFT ON PARALLEL APCHS TO ILS 27R AT ORD. I WAS FLYING AND THE CAPT WORKED THE RADIOS WITH ORD APCH. THE CTLR GAVE US A L TURN TO A HDG OF 360 DEGS. ONCE WE WERE LEVELED OUT ON THAT HDG THE TCASII ISSUED AN RA TO CLB AT 1200-1500 FPM AND INDICATED A TARGET MINUS 300 FT CLBING. DUE TO THE IMC CONDITIONS AND OUR COMPANIES RULES I COMMENCED A CLB AT 1500 FPM. THE CAPT TOLD ORD APCH OF THE RA AND OUR CLB. ORD APCH TOLD US TO IGNORE THE RA AND STATED OTHER ACR TFC 2000 FT ABOVE US. THE RA CONTINUED UNTIL WE REACHED 5800 FT MSL AND AT ONE POINT INDICATED THE TARGET AS MINUS 100 FT CLBING. ONCE THE TCASII ISSUED 'CLR OF CONFLICT' WE DSNDED IMMEDIATELY BACK DOWN TO 5000 FT MLS. THE WHOLE EVENT TOOK LESS THAN 1 MIN AND WE (NOR THE APCH CTLR) NEVER SAW THE INTRUDER. WE SUSPECT A TCASII SYS ERROR. A NORMAL APCH AND LNDG AT ORD WAS COMPLETED.

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.