Altitude deviation descent in response to TCASII.

Attributes
ACN	319212
Time
Date	199510
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 10300 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau tower : sjo
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival other arrival star : star enroute airway : zau
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : instrument pilot : commercial
Experience	flight time last 90 days : 240 flight time total : 5500 flight time type : 800
ASRS Report	319212
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 11000 flight time type : 475
ASRS Report	318966
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa
Resolutory Action	flight crew : took evasive action flight crew : returned to intended course or assigned course other
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

Our clearance was direct bearz intersection, 5 mi southeast of bearz at 11000 ft, and an assigned speed of 300 KTS. We were in an idle power descent. As we approached 12000 ft, we got a TA for traffic approximately 3 O'clock position, 3 mi, and about 500 ft below. Almost at that same instant, center called us to tell us that traffic just appeared on his scope. As center was talking, the TA changed to a 'descend, descend' RA. I disconnected the autoplt and responded to the RA. The captain informed ATC of our actions. The RA changed to 'monitor vertical speed,' then 'clear of conflict.' at this time we had descended through our assigned altitude of 11000 ft. I stopped the descent at 10300 ft, and began a climb back to our assigned altitude. We never got a visual sighting of the other aircraft, but center informed us it was 'fast moving, probably a jet.' supplemental information from acn 318966: there is not much that can be done in a 'see and avoid' environment to preclude this type of event. Perhaps the steep high speed dscnts that ATC mandates should be rethought.

Original NASA ASRS Text

Title: ALTDEV DSCNT IN RESPONSE TO TCASII.

Narrative: OUR CLRNC WAS DIRECT BEARZ INTXN, 5 MI SE OF BEARZ AT 11000 FT, AND AN ASSIGNED SPD OF 300 KTS. WE WERE IN AN IDLE PWR DSCNT. AS WE APCHED 12000 FT, WE GOT A TA FOR TFC APPROX 3 O'CLOCK POS, 3 MI, AND ABOUT 500 FT BELOW. ALMOST AT THAT SAME INSTANT, CTR CALLED US TO TELL US THAT TFC JUST APPEARED ON HIS SCOPE. AS CTR WAS TALKING, THE TA CHANGED TO A 'DSND, DSND' RA. I DISCONNECTED THE AUTOPLT AND RESPONDED TO THE RA. THE CAPT INFORMED ATC OF OUR ACTIONS. THE RA CHANGED TO 'MONITOR VERT SPD,' THEN 'CLR OF CONFLICT.' AT THIS TIME WE HAD DSNDED THROUGH OUR ASSIGNED ALT OF 11000 FT. I STOPPED THE DSCNT AT 10300 FT, AND BEGAN A CLB BACK TO OUR ASSIGNED ALT. WE NEVER GOT A VISUAL SIGHTING OF THE OTHER ACFT, BUT CTR INFORMED US IT WAS 'FAST MOVING, PROBABLY A JET.' SUPPLEMENTAL INFO FROM ACN 318966: THERE IS NOT MUCH THAT CAN BE DONE IN A 'SEE AND AVOID' ENVIRONMENT TO PRECLUDE THIS TYPE OF EVENT. PERHAPS THE STEEP HIGH SPD DSCNTS THAT ATC MANDATES SHOULD BE RETHOUGHT.

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.