Altitude deviation altitude excursion in flight crew response to TCASII RA.

Attributes
ACN	242772
Time
Date	199306
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : obk
State Reference	IL
Altitude	msl bound lower : 9800 msl bound upper : 10000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : on vectors enroute airway : zau
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller non radar : 6 controller radar : 5
ASRS Report	242772
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
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	faa : reviewed incident with flight crew
Miss Distance	vertical : 0
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Air carrier X, a TCASII equipped inbound aircraft to ord, level 10000 ft and assigned 300 KTS, following an air carrier Y large transport at 10000 ft and 300 KTS, inbound to ord. Air carrier X advised he had an RA descent and was leaving his assigned altitude. I told pilot only other aircraft in his immediate vicinity was at 4000 ft. Pilot said traffic was 11:30 at the same altitude. Only aircraft in that direction was the air carrier Y inbound to ord still at 10000 ft and still same direction. Air carrier X descended below 9800 ft before RA was cancelled and pilot returned to assigned altitude. At no time was separation lost on any aircraft, and at no time did there appear an aircraft IFR or VFR in the vicinity of air carrier X except as described. I would also like to state that the crew of air carrier X handled this event in a very professional manner and was a textbook example of how an event like this should be handled.

Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION IN FLC RESPONSE TO TCASII RA.

Narrative: ACR X, A TCASII EQUIPPED INBOUND ACFT TO ORD, LEVEL 10000 FT AND ASSIGNED 300 KTS, FOLLOWING AN ACR Y LGT AT 10000 FT AND 300 KTS, INBOUND TO ORD. ACR X ADVISED HE HAD AN RA DSCNT AND WAS LEAVING HIS ASSIGNED ALT. I TOLD PLT ONLY OTHER ACFT IN HIS IMMEDIATE VICINITY WAS AT 4000 FT. PLT SAID TFC WAS 11:30 AT THE SAME ALT. ONLY ACFT IN THAT DIRECTION WAS THE ACR Y INBOUND TO ORD STILL AT 10000 FT AND STILL SAME DIRECTION. ACR X DSNDED BELOW 9800 FT BEFORE RA WAS CANCELLED AND PLT RETURNED TO ASSIGNED ALT. AT NO TIME WAS SEPARATION LOST ON ANY ACFT, AND AT NO TIME DID THERE APPEAR AN ACFT IFR OR VFR IN THE VICINITY OF ACR X EXCEPT AS DESCRIBED. I WOULD ALSO LIKE TO STATE THAT THE CREW OF ACR X HANDLED THIS EVENT IN A VERY PROFESSIONAL MANNER AND WAS A TEXTBOOK EXAMPLE OF HOW AN EVENT LIKE THIS SHOULD BE HANDLED.

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.