Altitude deviation results from flight crew response to TCASII RA.

Attributes
ACN	230978
Time
Date	199301
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : cgt
State Reference	IL
Altitude	msl bound lower : 8750 msl bound upper : 9000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : psc
Operator	common carrier : air carrier
Make Model Name	Medium Transport, High Wing, 2 Turboprop Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute airway : zau
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
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 14000
ASRS Report	230978
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 500 vertical : 1000
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

While at 9000 ft MSL on IFR clearance, we had an IFR aircraft overtake us at 10000 ft MSL. The traffic caused our TCASII to issue an RA ('descend, descend') in conflict with ATC clearance. We descended to 8750 ft until the conflicting aircraft (an air carrier medium large transport) got us in sight. We then returned to our assigned altitude when we got him in sight. ATC (chicago center) indicated that no additional conflicts with other aircraft occurred. First time I have seen the TCASII issue an RA for 1000 ft vertical separation.

Original NASA ASRS Text

Title: ALTDEV RESULTS FROM FLC RESPONSE TO TCASII RA.

Narrative: WHILE AT 9000 FT MSL ON IFR CLRNC, WE HAD AN IFR ACFT OVERTAKE US AT 10000 FT MSL. THE TFC CAUSED OUR TCASII TO ISSUE AN RA ('DSND, DSND') IN CONFLICT WITH ATC CLRNC. WE DSNDED TO 8750 FT UNTIL THE CONFLICTING ACFT (AN ACR MLG) GOT US IN SIGHT. WE THEN RETURNED TO OUR ASSIGNED ALT WHEN WE GOT HIM IN SIGHT. ATC (CHICAGO CTR) INDICATED THAT NO ADDITIONAL CONFLICTS WITH OTHER ACFT OCCURRED. FIRST TIME I HAVE SEEN THE TCASII ISSUE AN RA FOR 1000 FT VERT SEPARATION.

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.