Narrative:

We were in level cruise flight when we received a TCASII traffic alert. It displayed traffic at approximately 1 O'clock, 3 mi, plus 3200 ft, descending. Watching the display, it became apparent that the 'target' was descending rapidly and closing fast. I began searching for the traffic (thinking fighter aircraft) but we received a RA (descend at greater than 1500 FPM) before obtaining a visual on the traffic. I disengaged the autoplt and began the descent while still looking for traffic. I then called center and told them of our deviation. I then observed the traffic which was either an F15 or F18 that appeared to have leveled off at about 15000 ft according to the TCASII and this appeared correct visually. The alert discontinued and we climbed back to 14000 ft. The descent had taken us to about 13500 ft. Center then said that the aircraft was a 'fighter, VFR, level at 17000 ft.' this aircraft was not at 17000 ft and if center knew of the traffic, he should have told us about it to possibly prevent the necessity to deviate from our altitude.

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Original NASA ASRS Text

Title: A MIL ACFT'S CLOSURE RATE CAUSED TCASII RA AND SUBSEQUENT 500 FT ALTDEV. ACR TURBOPROP FLC RPTED THEIR ALT DEV TO CTR CTLR.

Narrative: WE WERE IN LEVEL CRUISE FLT WHEN WE RECEIVED A TCASII TFC ALERT. IT DISPLAYED TFC AT APPROX 1 O'CLOCK, 3 MI, PLUS 3200 FT, DSNDING. WATCHING THE DISPLAY, IT BECAME APPARENT THAT THE 'TARGET' WAS DSNDING RAPIDLY AND CLOSING FAST. I BEGAN SEARCHING FOR THE TFC (THINKING FIGHTER ACFT) BUT WE RECEIVED A RA (DSND AT GREATER THAN 1500 FPM) BEFORE OBTAINING A VISUAL ON THE TFC. I DISENGAGED THE AUTOPLT AND BEGAN THE DSCNT WHILE STILL LOOKING FOR TFC. I THEN CALLED CTR AND TOLD THEM OF OUR DEV. I THEN OBSERVED THE TFC WHICH WAS EITHER AN F15 OR F18 THAT APPEARED TO HAVE LEVELED OFF AT ABOUT 15000 FT ACCORDING TO THE TCASII AND THIS APPEARED CORRECT VISUALLY. THE ALERT DISCONTINUED AND WE CLBED BACK TO 14000 FT. THE DSCNT HAD TAKEN US TO ABOUT 13500 FT. CTR THEN SAID THAT THE ACFT WAS A 'FIGHTER, VFR, LEVEL AT 17000 FT.' THIS ACFT WAS NOT AT 17000 FT AND IF CTR KNEW OF THE TFC, HE SHOULD HAVE TOLD US ABOUT IT TO POSSIBLY PREVENT THE NECESSITY TO DEVIATE FROM OUR 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.