TCASII mandates an altitude deviation altitude excursion by aircraft X.

Attributes
ACN	205765
Time
Date	199203
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : hve
State Reference	UT
Altitude	msl bound lower : 27500 msl bound upper : 28000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zlc
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : second officer
Qualification	pilot : flight engineer pilot : cfi pilot : atp
Experience	flight time last 90 days : 150 flight time total : 5000 flight time type : 700
ASRS Report	205765
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	Other
Miss Distance	horizontal : 12000 vertical : 350
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation other

Narrative:

Our flight was cruise confign. TCASII gave 'traffic, traffic.' was not visual but was displayed on TCASII approximately 1 O'clock, 5 mi descending to FL288. Soon thereafter TCASII gave demand (RA) 'descend, descend.' the first officer pwred back and started down. The captain advised ATC that we were descending out of FL280 for a RA. We leveled off at FL275 and visually located a widebody transport at 3 O'clock less than 2 mi and between 200-500 ft above us. Soon thereafter we climbed back to our altitude and TCASII soon showed widebody transport level at FL290. It appears widebody transport Y was maintaining their assigned altitude plus or minus 1000 ft.

Original NASA ASRS Text

Title: TCASII MANDATES AN ALTDEV ALT EXCURSION BY ACFT X.

Narrative: OUR FLT WAS CRUISE CONFIGN. TCASII GAVE 'TFC, TFC.' WAS NOT VISUAL BUT WAS DISPLAYED ON TCASII APPROX 1 O'CLOCK, 5 MI DSNDING TO FL288. SOON THEREAFTER TCASII GAVE DEMAND (RA) 'DSND, DSND.' THE FO PWRED BACK AND STARTED DOWN. THE CAPT ADVISED ATC THAT WE WERE DSNDING OUT OF FL280 FOR A RA. WE LEVELED OFF AT FL275 AND VISUALLY LOCATED A WDB AT 3 O'CLOCK LESS THAN 2 MI AND BTWN 200-500 FT ABOVE US. SOON THEREAFTER WE CLBED BACK TO OUR ALT AND TCASII SOON SHOWED WDB LEVEL AT FL290. IT APPEARS WDB Y WAS MAINTAINING THEIR ASSIGNED ALT PLUS OR MINUS 1000 FT.

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.