Narrative:

WX conditions at the airport were scattered clouds. Our departure instructions were runway heading, climb to 5000 ft. At approximately 1500 ft AGL we were cleared a right turn to 300 degrees, climb to 7000 ft. As we turned northwest the cloud density began to increase. Once established on the heading we were in numerous buildups with bases about 4000 ft and estimated tops about 15000 ft. As we neared our level off at 7000 ft, traffic was called to us at 11 O'clock, 3 mi at 7500 ft, a light single engine airplane, nebound. I saw the traffic and shortly thereafter the TCASII began to give a verbal RA to descend. I confirmed this on the vsi/TCASII display and it showed red everywhere except 2000 down where there was a small green area. I also noted that the traffic was displayed in red at 400 ft above our altitude. I looked back outside and crosschecked the TCASII and it now showed 300 ft above our altitude. I informed the captain that TCASII indicated the traffic was descending. TCASII was still issuing a RA to descend but we had remained at 7000 ft. The captain had started a slight left turn at this time to attempt to go behind the traffic. As the other airplane approached our 12 O'clock position he did a rather violent pushover as the captain performed a slight climb and continued his turn to the left. I estimate he passed within a quarter mi or less horizontally and slightly to our right when we were coalt. At about this same time the controller asked if we had the traffic in sight and I replied that I had. The other aircraft reported that he had us in sight and had thought we were at this altitude when he began his descent out of 7500 ft. The controller's response was that he thought we had a problem here. We then requested a change in heading to avoid a buildup and though we called several times we never received a reply. After several mins we were given a frequency change and the rest of the flight was uneventful. I believe the cause of this incident to be a lack of experience and situational awareness on the part of the pilot of the light single engine airplane. He was also operating in marginal VFR conditions at best. The number of buildups in the area completely obscured the horizon and made it necessary to maneuver a great deal to remain clear of clouds, much less VFR clrncs. I theorize that when he saw a large airplane only 500 ft below and with no horizon to use as a reference he mistakenly thought we were at his altitude, even though he had been advised by the controller of our altitude and position only a few moments earlier, and had no clearance to descend. I am also concerned by the lack of response of the controller immediately after this incident. He was unable to give us clearance to deviate around buildups or avoid other traffic and would only instruct us to remain on his frequency. This seemed unnecessary since he had not given us another. There was other traffic in the area and I do not feel confident he would have been able to advise us of another conflict had the need arisen. The entire incident would not have developed if the controller had turned us to a heading of less than 300 degrees, or held us at a lower altitude. Although what he did was completely legal, either of these alternatives would have been more conservative and safer. This incident has once again convinced me there is no substitute for 'see and avoid.' had we followed the initial TCASII instruction we would most likely have collided. This is not to say that the TCASII system did not function correctly or is inadequate. It was a great help in analyzing this situation. However, it cannot, and is not designed to anticipate human behavior.

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Original NASA ASRS Text

Title: VFR ACFT DSNDS INTO FLT PATH OF ACR MAINTAINING 7000.

Narrative: WX CONDITIONS AT THE ARPT WERE SCATTERED CLOUDS. OUR DEP INSTRUCTIONS WERE RWY HDG, CLB TO 5000 FT. AT APPROX 1500 FT AGL WE WERE CLRED A R TURN TO 300 DEGS, CLB TO 7000 FT. AS WE TURNED NW THE CLOUD DENSITY BEGAN TO INCREASE. ONCE ESTABLISHED ON THE HDG WE WERE IN NUMEROUS BUILDUPS WITH BASES ABOUT 4000 FT AND ESTIMATED TOPS ABOUT 15000 FT. AS WE NEARED OUR LEVEL OFF AT 7000 FT, TFC WAS CALLED TO US AT 11 O'CLOCK, 3 MI AT 7500 FT, A LIGHT SINGLE ENG AIRPLANE, NEBOUND. I SAW THE TFC AND SHORTLY THEREAFTER THE TCASII BEGAN TO GIVE A VERBAL RA TO DSND. I CONFIRMED THIS ON THE VSI/TCASII DISPLAY AND IT SHOWED RED EVERYWHERE EXCEPT 2000 DOWN WHERE THERE WAS A SMALL GREEN AREA. I ALSO NOTED THAT THE TFC WAS DISPLAYED IN RED AT 400 FT ABOVE OUR ALT. I LOOKED BACK OUTSIDE AND XCHKED THE TCASII AND IT NOW SHOWED 300 FT ABOVE OUR ALT. I INFORMED THE CAPT THAT TCASII INDICATED THE TFC WAS DSNDING. TCASII WAS STILL ISSUING A RA TO DSND BUT WE HAD REMAINED AT 7000 FT. THE CAPT HAD STARTED A SLIGHT L TURN AT THIS TIME TO ATTEMPT TO GO BEHIND THE TFC. AS THE OTHER AIRPLANE APCHED OUR 12 O'CLOCK POS HE DID A RATHER VIOLENT PUSHOVER AS THE CAPT PERFORMED A SLIGHT CLB AND CONTINUED HIS TURN TO THE L. I ESTIMATE HE PASSED WITHIN A QUARTER MI OR LESS HORIZONTALLY AND SLIGHTLY TO OUR R WHEN WE WERE COALT. AT ABOUT THIS SAME TIME THE CTLR ASKED IF WE HAD THE TFC IN SIGHT AND I REPLIED THAT I HAD. THE OTHER ACFT RPTED THAT HE HAD US IN SIGHT AND HAD THOUGHT WE WERE AT THIS ALT WHEN HE BEGAN HIS DSCNT OUT OF 7500 FT. THE CTLR'S RESPONSE WAS THAT HE THOUGHT WE HAD A PROBLEM HERE. WE THEN REQUESTED A CHANGE IN HDG TO AVOID A BUILDUP AND THOUGH WE CALLED SEVERAL TIMES WE NEVER RECEIVED A REPLY. AFTER SEVERAL MINS WE WERE GIVEN A FREQ CHANGE AND THE REST OF THE FLT WAS UNEVENTFUL. I BELIEVE THE CAUSE OF THIS INCIDENT TO BE A LACK OF EXPERIENCE AND SITUATIONAL AWARENESS ON THE PART OF THE PLT OF THE LIGHT SINGLE ENG AIRPLANE. HE WAS ALSO OPERATING IN MARGINAL VFR CONDITIONS AT BEST. THE NUMBER OF BUILDUPS IN THE AREA COMPLETELY OBSCURED THE HORIZON AND MADE IT NECESSARY TO MANEUVER A GREAT DEAL TO REMAIN CLR OF CLOUDS, MUCH LESS VFR CLRNCS. I THEORIZE THAT WHEN HE SAW A LARGE AIRPLANE ONLY 500 FT BELOW AND WITH NO HORIZON TO USE AS A REF HE MISTAKENLY THOUGHT WE WERE AT HIS ALT, EVEN THOUGH HE HAD BEEN ADVISED BY THE CTLR OF OUR ALT AND POS ONLY A FEW MOMENTS EARLIER, AND HAD NO CLRNC TO DSND. I AM ALSO CONCERNED BY THE LACK OF RESPONSE OF THE CTLR IMMEDIATELY AFTER THIS INCIDENT. HE WAS UNABLE TO GIVE US CLRNC TO DEVIATE AROUND BUILDUPS OR AVOID OTHER TFC AND WOULD ONLY INSTRUCT US TO REMAIN ON HIS FREQ. THIS SEEMED UNNECESSARY SINCE HE HAD NOT GIVEN US ANOTHER. THERE WAS OTHER TFC IN THE AREA AND I DO NOT FEEL CONFIDENT HE WOULD HAVE BEEN ABLE TO ADVISE US OF ANOTHER CONFLICT HAD THE NEED ARISEN. THE ENTIRE INCIDENT WOULD NOT HAVE DEVELOPED IF THE CTLR HAD TURNED US TO A HDG OF LESS THAN 300 DEGS, OR HELD US AT A LOWER ALT. ALTHOUGH WHAT HE DID WAS COMPLETELY LEGAL, EITHER OF THESE ALTERNATIVES WOULD HAVE BEEN MORE CONSERVATIVE AND SAFER. THIS INCIDENT HAS ONCE AGAIN CONVINCED ME THERE IS NO SUBSTITUTE FOR 'SEE AND AVOID.' HAD WE FOLLOWED THE INITIAL TCASII INSTRUCTION WE WOULD MOST LIKELY HAVE COLLIDED. THIS IS NOT TO SAY THAT THE TCASII SYS DID NOT FUNCTION CORRECTLY OR IS INADEQUATE. IT WAS A GREAT HELP IN ANALYZING THIS SITUATION. HOWEVER, IT CANNOT, AND IS NOT DESIGNED TO ANTICIPATE HUMAN BEHAVIOR.

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.