An E120 crew was alerted by a TCASII TA, then acquired the aircraft visually.

Attributes
ACN	511048
Time
Date	200103
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : lyn.airport
State Reference	VA
Altitude	msl single value : 4000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : roa.tracon
Operator	common carrier : air carrier
Make Model Name	Brasilia EMB-120 All Series
Operating Under FAR Part	Part 121
Navigation In Use	other vortac
Flight Phase	climbout : initial
Route In Use	departure : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : roa.tracon
Operator	general aviation : personal
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	descent : vacating altitude
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi pilot : flight engineer
Experience	flight time last 90 days : 260 flight time total : 3000 flight time type : 1500
ASRS Report	511048
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude
Independent Detector	aircraft equipment : tcas other flight crewa other flight crewb
Resolutory Action	controller : issued advisory flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 500
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

We were cleared after takeoff to fly runway heading 220 degrees, climb to 4000 ft MSL. After departure we were told to contact roa departure on frequency 135.00. We were told to watch for traffic 12 O'clock position heading sbound. Immediately after contacting roa approach, we were told to go direct bzm. We then received a TA (tcasi). We had a threat at 5 mi 800 ft above us descending. At about 3-5 mi we acquired the cessna visually. We were on a direct collision course. The first officer was PF. I ordered him to push the nose over and descend immediately. The cessna passed directly over the top of us. We cleared by 500 ft. There is no doubt in my mind that had we not initiated our descent when we did we would have hit the other aircraft. The cessna took no action at all, and I do not believe he was aware of our aircraft at all. When I informed roa departure, they told me there was nothing he could do about that. I realize they are not always in contact with VFR aircraft. I don't think controllers realize that a cessna is very hard to spot visually. It is pretty much impossible to acquire one further out than 5 mi. I think lyh needs better radar coverage so they can better separate IFR and VFR traffic. Roa telling me they can't do anything about that would not mean much if airplanes collide.

Original NASA ASRS Text

Title: AN E120 CREW WAS ALERTED BY A TCASII TA, THEN ACQUIRED THE ACFT VISUALLY.

Narrative: WE WERE CLRED AFTER TKOF TO FLY RWY HDG 220 DEGS, CLB TO 4000 FT MSL. AFTER DEP WE WERE TOLD TO CONTACT ROA DEP ON FREQ 135.00. WE WERE TOLD TO WATCH FOR TFC 12 O'CLOCK POS HDG SBOUND. IMMEDIATELY AFTER CONTACTING ROA APCH, WE WERE TOLD TO GO DIRECT BZM. WE THEN RECEIVED A TA (TCASI). WE HAD A THREAT AT 5 MI 800 FT ABOVE US DSNDING. AT ABOUT 3-5 MI WE ACQUIRED THE CESSNA VISUALLY. WE WERE ON A DIRECT COLLISION COURSE. THE FO WAS PF. I ORDERED HIM TO PUSH THE NOSE OVER AND DSND IMMEDIATELY. THE CESSNA PASSED DIRECTLY OVER THE TOP OF US. WE CLRED BY 500 FT. THERE IS NO DOUBT IN MY MIND THAT HAD WE NOT INITIATED OUR DSCNT WHEN WE DID WE WOULD HAVE HIT THE OTHER ACFT. THE CESSNA TOOK NO ACTION AT ALL, AND I DO NOT BELIEVE HE WAS AWARE OF OUR ACFT AT ALL. WHEN I INFORMED ROA DEP, THEY TOLD ME THERE WAS NOTHING HE COULD DO ABOUT THAT. I REALIZE THEY ARE NOT ALWAYS IN CONTACT WITH VFR ACFT. I DON'T THINK CTLRS REALIZE THAT A CESSNA IS VERY HARD TO SPOT VISUALLY. IT IS PRETTY MUCH IMPOSSIBLE TO ACQUIRE ONE FURTHER OUT THAN 5 MI. I THINK LYH NEEDS BETTER RADAR COVERAGE SO THEY CAN BETTER SEPARATE IFR AND VFR TFC. ROA TELLING ME THEY CAN'T DO ANYTHING ABOUT THAT WOULD NOT MEAN MUCH IF AIRPLANES COLLIDE.

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.