Narrative:

On nov/xa/08 at XA05; we were receiving radar vectors for ZZZ1 from TRACON close to V437 on the abc VOR level at 3000 ft on an IFR flight plan from ZZZ to ZZZ1 when we noticed a target on the TAS screen; about 3500 ft above us and 1 mi behind us; descending. The target was descending at a high rate; so that about 45 seconds later it was above us and slightly to the right; at 500 ft above us. We received a TA from onboard TAS; and about 5 seconds later the target was only 200 ft above us. Noting the extreme closure rate and having just received the TA; I disconnected the autoplt and violently banked the aircraft left and slightly down while adding power. The pilot in the right seat saw the aircraft pass about 100 ft below us and 50 ft to the right. I only made visual contact with the aircraft as it passed below to the left; about 500 ft below us at that time. The other aircraft was a light piston twin and descended about 30 degrees nose down to about 300-400 ft AGL; apparently with the right engine feathered. I initially thought they were going to crash land; which I noted to the other pilot. The other aircraft then; however; pulled up abruptly and zoom-climbed to about 1500 ft AGL before we lost sight. It appeared that they were engaging in a practice emergency descent with the right engine feathered for some reason. This occurred about 4 NM west of alert area. About 5 seconds after evasive action was taken; the ATC controller called us frantically and advised of traffic at the same altitude and too close to tell direction. We didn't respond the first time since we were still shaking. On his second call we told him we took evasive action and were heading to the left of the assigned vector. There were at least 6 other targets showing on the traffic screen within 6 NM of us; within +/-300 ft. Our flight then proceeded for an uneventful landing at ZZZ about 15 mins later. Without the onboard TAS; I am positive that the twin engine airplane would have collided with our airplane midair. Only radical evasive action on our part prevented a midair collision; as the other airplane likely never saw us and never took any evasive action. I would speculate that a training flight strayed out of the nearby alert area. After the incident; I called TRACON on the phone and advised them.

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Original NASA ASRS Text

Title: A HIGH WING LIGHT AIRCRAFT EXPERIENCED AN NMAC WITH A LIGHT TWIN IN THE VICINITY OF OPF.

Narrative: ON NOV/XA/08 AT XA05; WE WERE RECEIVING RADAR VECTORS FOR ZZZ1 FROM TRACON CLOSE TO V437 ON THE ABC VOR LEVEL AT 3000 FT ON AN IFR FLT PLAN FROM ZZZ TO ZZZ1 WHEN WE NOTICED A TARGET ON THE TAS SCREEN; ABOUT 3500 FT ABOVE US AND 1 MI BEHIND US; DSNDING. THE TARGET WAS DSNDING AT A HIGH RATE; SO THAT ABOUT 45 SECONDS LATER IT WAS ABOVE US AND SLIGHTLY TO THE R; AT 500 FT ABOVE US. WE RECEIVED A TA FROM ONBOARD TAS; AND ABOUT 5 SECONDS LATER THE TARGET WAS ONLY 200 FT ABOVE US. NOTING THE EXTREME CLOSURE RATE AND HAVING JUST RECEIVED THE TA; I DISCONNECTED THE AUTOPLT AND VIOLENTLY BANKED THE ACFT L AND SLIGHTLY DOWN WHILE ADDING PWR. THE PLT IN THE R SEAT SAW THE ACFT PASS ABOUT 100 FT BELOW US AND 50 FT TO THE R. I ONLY MADE VISUAL CONTACT WITH THE ACFT AS IT PASSED BELOW TO THE L; ABOUT 500 FT BELOW US AT THAT TIME. THE OTHER ACFT WAS A LIGHT PISTON TWIN AND DSNDED ABOUT 30 DEGS NOSE DOWN TO ABOUT 300-400 FT AGL; APPARENTLY WITH THE R ENG FEATHERED. I INITIALLY THOUGHT THEY WERE GOING TO CRASH LAND; WHICH I NOTED TO THE OTHER PLT. THE OTHER ACFT THEN; HOWEVER; PULLED UP ABRUPTLY AND ZOOM-CLBED TO ABOUT 1500 FT AGL BEFORE WE LOST SIGHT. IT APPEARED THAT THEY WERE ENGAGING IN A PRACTICE EMER DSCNT WITH THE R ENG FEATHERED FOR SOME REASON. THIS OCCURRED ABOUT 4 NM W OF ALERT AREA. ABOUT 5 SECONDS AFTER EVASIVE ACTION WAS TAKEN; THE ATC CTLR CALLED US FRANTICALLY AND ADVISED OF TFC AT THE SAME ALT AND TOO CLOSE TO TELL DIRECTION. WE DIDN'T RESPOND THE FIRST TIME SINCE WE WERE STILL SHAKING. ON HIS SECOND CALL WE TOLD HIM WE TOOK EVASIVE ACTION AND WERE HEADING TO THE L OF THE ASSIGNED VECTOR. THERE WERE AT LEAST 6 OTHER TARGETS SHOWING ON THE TFC SCREEN WITHIN 6 NM OF US; WITHIN +/-300 FT. OUR FLT THEN PROCEEDED FOR AN UNEVENTFUL LNDG AT ZZZ ABOUT 15 MINS LATER. WITHOUT THE ONBOARD TAS; I AM POSITIVE THAT THE TWIN ENG AIRPLANE WOULD HAVE COLLIDED WITH OUR AIRPLANE MIDAIR. ONLY RADICAL EVASIVE ACTION ON OUR PART PREVENTED A MIDAIR COLLISION; AS THE OTHER AIRPLANE LIKELY NEVER SAW US AND NEVER TOOK ANY EVASIVE ACTION. I WOULD SPECULATE THAT A TRAINING FLT STRAYED OUT OF THE NEARBY ALERT AREA. AFTER THE INCIDENT; I CALLED TRACON ON THE PHONE AND ADVISED THEM.

Data retrieved from NASA's ASRS site as of May 2009 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.