Narrative:

I was in cruise confign in my bell 407, at about 127 KTS and 7500 ft MSL bound from stp to sbm on a GPS track between the 2 points. Many aircraft had been heard on 118.5 (osh CTAF), and many aircraft had been seen visually and on my bfg tcasi unit over its 6 NM range. Without any other kinds of indication, the tcasi unit sounded a 'traffic, traffic,' advisory, and I looked down into the cockpit to see the location of the blip on the tcasi screen. There was clearly depicted a target right on top of the center 300 ft above me. I immediately hit the range reduction button to expand to the 2 mi scale, and a target was then very slightly separated below the center of the instrument, and still with an altitude difference of 300 ft directly above and behind my helicopter, with the target blip slightly overlapping the center indicator on the instrument. I then confirmed that the target indicated 300 ft above (+) me and descending, and then quickly reduced collective and nosed over simultaneously with a banking right roll of 90 degrees. The blip then started indicating an up arrow which meant it was climbing away from me, and separated very rapidly in what appeared to be a westerly direction. At the completion of my 180 degree turn, the target was well separated and climbing very rapidly.

Google
 

Original NASA ASRS Text

Title: A COMMERCIAL INST RATED HELI PLT REACTS TO A TCASI TA.

Narrative: I WAS IN CRUISE CONFIGN IN MY BELL 407, AT ABOUT 127 KTS AND 7500 FT MSL BOUND FROM STP TO SBM ON A GPS TRACK BTWN THE 2 POINTS. MANY ACFT HAD BEEN HEARD ON 118.5 (OSH CTAF), AND MANY ACFT HAD BEEN SEEN VISUALLY AND ON MY BFG TCASI UNIT OVER ITS 6 NM RANGE. WITHOUT ANY OTHER KINDS OF INDICATION, THE TCASI UNIT SOUNDED A 'TFC, TFC,' ADVISORY, AND I LOOKED DOWN INTO THE COCKPIT TO SEE THE LOCATION OF THE BLIP ON THE TCASI SCREEN. THERE WAS CLRLY DEPICTED A TARGET RIGHT ON TOP OF THE CTR 300 FT ABOVE ME. I IMMEDIATELY HIT THE RANGE REDUCTION BUTTON TO EXPAND TO THE 2 MI SCALE, AND A TARGET WAS THEN VERY SLIGHTLY SEPARATED BELOW THE CTR OF THE INST, AND STILL WITH AN ALT DIFFERENCE OF 300 FT DIRECTLY ABOVE AND BEHIND MY HELI, WITH THE TARGET BLIP SLIGHTLY OVERLAPPING THE CTR INDICATOR ON THE INST. I THEN CONFIRMED THAT THE TARGET INDICATED 300 FT ABOVE (+) ME AND DSNDING, AND THEN QUICKLY REDUCED COLLECTIVE AND NOSED OVER SIMULTANEOUSLY WITH A BANKING R ROLL OF 90 DEGS. THE BLIP THEN STARTED INDICATING AN UP ARROW WHICH MEANT IT WAS CLBING AWAY FROM ME, AND SEPARATED VERY RAPIDLY IN WHAT APPEARED TO BE A WESTERLY DIRECTION. AT THE COMPLETION OF MY 180 DEG TURN, THE TARGET WAS WELL SEPARATED AND CLBING VERY RAPIDLY.

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.