False TCASII RA almost causes medium large transport to descend into traffic.

Attributes
ACN	240908
Time
Date	199305
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : fak
State Reference	VA
Altitude	msl bound lower : 26700 msl bound upper : 27000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 210 flight time total : 9800 flight time type : 25
ASRS Report	240908
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other other : unspecified atc
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

At FL270 eastbound between montebello and flat rock VOR, TCASII provided a TA on wbound traffic at FL260 (yellow symbol) at minus 10. Approximately 30 seconds after the alert, an RA given to 'monitor vertical speed.' traffic target that was previously on the vvi display now had a red symbol a plus 800 ft on the altitude readout. TCASII vvi commanded no climb at first. Approximately 10 seconds after the first RA, a second RA was given to 'descend, descend.' traffic could not be found and descent was initiated by first officer who was flying. Vvi commanded descent at 1500 FPM. ZTL was immediately asked about additional traffic above us. We were informed we only had traffic at FL260. Descent was stopped at FL267 and all RA information disappeared from vvi. At no time was the traffic visually acquired. We were very alarmed that TCASII would command descent into oncoming traffic! It is my opinion the FL260 traffic's mode C was sending information causing the false target, but in the areas of high performance military, one can't second guess. I am filing this report for your documentation and ours.

Original NASA ASRS Text

Title: FALSE TCASII RA ALMOST CAUSES MLG TO DSND INTO TFC.

Narrative: AT FL270 EBOUND BTWN MONTEBELLO AND FLAT ROCK VOR, TCASII PROVIDED A TA ON WBOUND TFC AT FL260 (YELLOW SYMBOL) AT MINUS 10. APPROX 30 SECONDS AFTER THE ALERT, AN RA GIVEN TO 'MONITOR VERT SPD.' TFC TARGET THAT WAS PREVIOUSLY ON THE VVI DISPLAY NOW HAD A RED SYMBOL A PLUS 800 FT ON THE ALT READOUT. TCASII VVI COMMANDED NO CLB AT FIRST. APPROX 10 SECONDS AFTER THE FIRST RA, A SECOND RA WAS GIVEN TO 'DSND, DSND.' TFC COULD NOT BE FOUND AND DSCNT WAS INITIATED BY FO WHO WAS FLYING. VVI COMMANDED DSCNT AT 1500 FPM. ZTL WAS IMMEDIATELY ASKED ABOUT ADDITIONAL TFC ABOVE US. WE WERE INFORMED WE ONLY HAD TFC AT FL260. DSCNT WAS STOPPED AT FL267 AND ALL RA INFO DISAPPEARED FROM VVI. AT NO TIME WAS THE TFC VISUALLY ACQUIRED. WE WERE VERY ALARMED THAT TCASII WOULD COMMAND DSCNT INTO ONCOMING TFC! IT IS MY OPINION THE FL260 TFC'S MODE C WAS SENDING INFO CAUSING THE FALSE TARGET, BUT IN THE AREAS OF HIGH PERFORMANCE MIL, ONE CAN'T SECOND GUESS. I AM FILING THIS RPT FOR YOUR DOCUMENTATION AND OURS.

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.