C182 pilot has a TCAS alert while in cruise.

Attributes
ACN	716736
Time
Date	200611
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : zjx.artcc
State Reference	FL
Altitude	msl single value : 6000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zjx.artcc
Operator	general aviation : corporate
Make Model Name	Skylane 182/RG Turbo Skylane/RG
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zjx.artcc
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent : intermediate altitude
Flight Plan	VFR
Person 1
Affiliation	company : corporate
Function	flight crew : single pilot
Qualification	pilot : cfi pilot : instrument pilot : multi engine pilot : commercial
Experience	flight time last 90 days : 50 flight time total : 2731 flight time type : 700
ASRS Report	716736
Person 2
Affiliation	government : faa
Function	controller : traffic management controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance aircraft equipment problem : less severe
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued advisory
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 2500 vertical : 200
Supplementary
Problem Areas	ATC Human Performance Airspace Structure Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

I was given a TA by ATC that a VFR aircraft was at 12 O'clock position; 5 mi and 500 ft above my altitude; opposite direction; 'moving fast across the ground.' shortly after this advisory the controller said the other aircraft had started a descent. I was scanning for the aircraft but could not see it. TCAS then announced traffic. I still could not visually locate the traffic. The controller then issued a traffic alert and recommended a 15 degree left turn. TCAS was showing the aircraft at 200 ft above; less than a mi. I initiated a descending left turn to avoid the traffic. I had turned 20 degrees to the left and descended 500 ft. After leveling off at 5500 ft the controller told me that I must maintain 6000 ft. I started a climb back to 6000 ft and told the controller that I had descended because the traffic was too close. He repeated that I should not have descended and I must maintain 6000 ft. I think I should have been given a turn to avoid the traffic sooner; at 5 mi to avoid this situation.

Original NASA ASRS Text

Title: C182 PLT HAS A TCAS ALERT WHILE IN CRUISE.

Narrative: I WAS GIVEN A TA BY ATC THAT A VFR ACFT WAS AT 12 O'CLOCK POS; 5 MI AND 500 FT ABOVE MY ALT; OPPOSITE DIRECTION; 'MOVING FAST ACROSS THE GND.' SHORTLY AFTER THIS ADVISORY THE CTLR SAID THE OTHER ACFT HAD STARTED A DSCNT. I WAS SCANNING FOR THE ACFT BUT COULD NOT SEE IT. TCAS THEN ANNOUNCED TFC. I STILL COULD NOT VISUALLY LOCATE THE TFC. THE CTLR THEN ISSUED A TFC ALERT AND RECOMMENDED A 15 DEG L TURN. TCAS WAS SHOWING THE ACFT AT 200 FT ABOVE; LESS THAN A MI. I INITIATED A DSNDING L TURN TO AVOID THE TFC. I HAD TURNED 20 DEGS TO THE L AND DSNDED 500 FT. AFTER LEVELING OFF AT 5500 FT THE CTLR TOLD ME THAT I MUST MAINTAIN 6000 FT. I STARTED A CLB BACK TO 6000 FT AND TOLD THE CTLR THAT I HAD DSNDED BECAUSE THE TFC WAS TOO CLOSE. HE REPEATED THAT I SHOULD NOT HAVE DSNDED AND I MUST MAINTAIN 6000 FT. I THINK I SHOULD HAVE BEEN GIVEN A TURN TO AVOID THE TFC SOONER; AT 5 MI TO AVOID THIS SITUATION.

Data retrieved from NASA's ASRS site as of January 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.