TCASII alert caused flight crew to excursion from assigned altitude of FL350.

Attributes
ACN	180358
Time
Date	199106
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : btg
State Reference	WA
Altitude	msl bound lower : 35000 msl bound upper : 35800
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zse
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	climbout : initial cruise other descent other
Route In Use	enroute airway : zte
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 180 flight time total : 11000
ASRS Report	180358
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : atp pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : far other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While in cruise flight overhead btg VOR at FL350 our TCAS generated a rs. During a period of no more than 15 seconds we received a TA, 'traffic, traffic.' followed by a preventive RA, 'monitor vertical speed' (vsi red caution zone from 0-6000 FPM down), followed by the RA, 'climb, climb' (vsi red from 6000 down to 1500 up). At no time did we remember seeing the red RA square and its accompanying data tag on the vsi. Company policy is to comply with TCAS RA unless pilot judges it to be unsafe. So 1500 FPM climb was initiated while copilot visually scanned outside and advised ATC of our intentions. At 35800' TCAS announced, 'clear of conflict,' and descend back to FL350 was initiated. ATC said no traffic was observed that could account for this incident. As we were descending back to FL350 we noticed a yellow TA circle nearly superimposed on the aircraft symbol on the vsi.

Original NASA ASRS Text

Title: TCASII ALERT CAUSED FLT CREW TO EXCURSION FROM ASSIGNED ALT OF FL350.

Narrative: WHILE IN CRUISE FLT OVERHEAD BTG VOR AT FL350 OUR TCAS GENERATED A RS. DURING A PERIOD OF NO MORE THAN 15 SECS WE RECEIVED A TA, 'TFC, TFC.' FOLLOWED BY A PREVENTIVE RA, 'MONITOR VERT SPD' (VSI RED CAUTION ZONE FROM 0-6000 FPM DOWN), FOLLOWED BY THE RA, 'CLB, CLB' (VSI RED FROM 6000 DOWN TO 1500 UP). AT NO TIME DID WE REMEMBER SEEING THE RED RA SQUARE AND ITS ACCOMPANYING DATA TAG ON THE VSI. COMPANY POLICY IS TO COMPLY WITH TCAS RA UNLESS PLT JUDGES IT TO BE UNSAFE. SO 1500 FPM CLB WAS INITIATED WHILE COPLT VISUALLY SCANNED OUTSIDE AND ADVISED ATC OF OUR INTENTIONS. AT 35800' TCAS ANNOUNCED, 'CLR OF CONFLICT,' AND DSND BACK TO FL350 WAS INITIATED. ATC SAID NO TFC WAS OBSERVED THAT COULD ACCOUNT FOR THIS INCIDENT. AS WE WERE DSNDING BACK TO FL350 WE NOTICED A YELLOW TA CIRCLE NEARLY SUPERIMPOSED ON THE ACFT SYMBOL ON THE VSI.

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.