An air carrier mdt climbed in response to a TCASII command.

Attributes
ACN	224411
Time
Date	199210
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 7000 msl bound upper : 7300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Medium Transport, Low Wing, 2 Turboprop 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 : first officer
Qualification	pilot : instrument pilot : commercial
Experience	flight time last 90 days : 250 flight time total : 6000
ASRS Report	224411
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 15000
ASRS Report	224310
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : took evasive action
Consequence	Other
Miss Distance	vertical : 3500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation other

Narrative:

Flight from osh to ord with a stop at mke. We were handed off to ord approach at 7000 ft. Shortly thereafter, we received a 'TA' amber target at our 1130 to 12 O'clock position (no altitude information). The target turned into an 'RA' red target within seconds. At this moment, we were commanded to 'climb.' the climb was executed, and out of 7200 ft, the target vanished. The TCASII never tracked the target further and it never said that we were 'clear of conflict.' we deviated from our assigned altitude of 7000 ft up to 7300 ft. At the moment of the 'RA climb' ATC was advised. After returning to 7000 ft, ATC said that they had a VFR aircraft at 3500 in that area. Nothing more was said about the deviation. I wonder, could a sudden climb or aerobatics cause a closure signal with 3500 ft separation? Supplemental information from acn 224310: we can only surmise the VFR target was doing air work and initiated a climb just as we approached him. That's only a guess.

Original NASA ASRS Text

Title: AN ACR MDT CLBED IN RESPONSE TO A TCASII COMMAND.

Narrative: FLT FROM OSH TO ORD WITH A STOP AT MKE. WE WERE HANDED OFF TO ORD APCH AT 7000 FT. SHORTLY THEREAFTER, WE RECEIVED A 'TA' AMBER TARGET AT OUR 1130 TO 12 O'CLOCK POS (NO ALT INFO). THE TARGET TURNED INTO AN 'RA' RED TARGET WITHIN SECONDS. AT THIS MOMENT, WE WERE COMMANDED TO 'CLB.' THE CLB WAS EXECUTED, AND OUT OF 7200 FT, THE TARGET VANISHED. THE TCASII NEVER TRACKED THE TARGET FURTHER AND IT NEVER SAID THAT WE WERE 'CLR OF CONFLICT.' WE DEVIATED FROM OUR ASSIGNED ALT OF 7000 FT UP TO 7300 FT. AT THE MOMENT OF THE 'RA CLB' ATC WAS ADVISED. AFTER RETURNING TO 7000 FT, ATC SAID THAT THEY HAD A VFR ACFT AT 3500 IN THAT AREA. NOTHING MORE WAS SAID ABOUT THE DEV. I WONDER, COULD A SUDDEN CLB OR AEROBATICS CAUSE A CLOSURE SIGNAL WITH 3500 FT SEPARATION? SUPPLEMENTAL INFO FROM ACN 224310: WE CAN ONLY SURMISE THE VFR TARGET WAS DOING AIR WORK AND INITIATED A CLB JUST AS WE APCHED HIM. THAT'S ONLY A GUESS.

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.