Air carrier large transport altitude deviation in response to TCASII RA.

Attributes
ACN	176286
Time
Date	199104
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : enl
State Reference	IL
Altitude	msl bound lower : 27500 msl bound upper : 28000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid tracon : psc
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute airway : zid
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 9000 flight time type : 1600
ASRS Report	176286
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Miss Distance	horizontal : 1000 vertical : 1000
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Climbing to cruise of assigned altitude FL390 we were held to FL280 for traffic. While cruising at FL280 TCAS system announced 'traffic' and yellow symbol on TCAS screen observed between 11:30 to 12 O'clock indicating traffic was 1700' above descending. TCAS announce 'descend', symbol was red and red arc on ivsi with green fly to arc at about -1000' down on ivsi. Autoplt was disconnected and descent commenced. After descending 500', TCAS announced clear of traffic. We climbed back to FL280. Due to frequency congestion we were unable to advise ATC immediately of our action. Center advised traffic in question was descending to FL290 from FL310. Traffic was never visly acquired probably because we were flying into the sun. TCAS system is unable to detect other aircraft intent, ie, due to level at assigned altitude.

Original NASA ASRS Text

Title: ACR LGT ALT DEVIATION IN RESPONSE TO TCASII RA.

Narrative: CLBING TO CRUISE OF ASSIGNED ALT FL390 WE WERE HELD TO FL280 FOR TFC. WHILE CRUISING AT FL280 TCAS SYS ANNOUNCED 'TFC' AND YELLOW SYMBOL ON TCAS SCREEN OBSERVED BTWN 11:30 TO 12 O'CLOCK INDICATING TFC WAS 1700' ABOVE DSNDING. TCAS ANNOUNCE 'DSND', SYMBOL WAS RED AND RED ARC ON IVSI WITH GREEN FLY TO ARC AT ABOUT -1000' DOWN ON IVSI. AUTOPLT WAS DISCONNECTED AND DSNT COMMENCED. AFTER DSNDING 500', TCAS ANNOUNCED CLR OF TFC. WE CLBED BACK TO FL280. DUE TO FREQ CONGESTION WE WERE UNABLE TO ADVISE ATC IMMEDIATELY OF OUR ACTION. CTR ADVISED TFC IN QUESTION WAS DSNDING TO FL290 FROM FL310. TFC WAS NEVER VISLY ACQUIRED PROBABLY BECAUSE WE WERE FLYING INTO THE SUN. TCAS SYS IS UNABLE TO DETECT OTHER ACFT INTENT, IE, DUE TO LEVEL AT ASSIGNED ALT.

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.