IFR C172 vectored to ILS by grb controller experienced near midair collision with VFR aircraft.

Attributes
ACN	588401
Time
Date	200307
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : grb.tracon
State Reference	WI
Altitude	msl single value : 3000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : grb.tracon
Operator	general aviation : personal
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Navigation In Use	ils localizer & glide slope : 29
Flight Phase	descent : approach
Route In Use	arrival : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tower : atw.tower
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise : level
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : instrument pilot : private
Experience	flight time last 90 days : 20 flight time total : 480 flight time type : 400
ASRS Report	588401
Person 2
Affiliation	other
Function	flight crew : single pilot
Events
Anomaly	conflict : nmac
Independent Detector	other controllera other controllerb
Resolutory Action	controller : issued advisory
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 400
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Inter Facility Coordination Failure

Narrative:

I was on an IFR flight plan in VMC from 57C to atw. I was handed off from ZAU to grb approach. Shortly after the handoff, grb asked me if I had traffic at my 3 O'clock position, in real close. I checked and couldn't see anything. Then grb said the target disappeared and they suspected a 'split beacon.' I was on a 360 degree vector up the east side of lake winnebago, being vectored for the ILS runway 29 at atw. The intercept takes place on the north side or the lake. Grb turned me in on the intercept and cleared me for the approach. I was at 3000 ft. Shortly after making the turn inbound, they told me to call atw tower. At the same time, I spotted the other plane directly above me and slightly ahead. We had 300-500 ft of vertical separation. I reported it to grb approach, and they said it must not have been a split beacon after all. Our 2 targets were merged the entire time. Grb said they were not talking to him. When I switched to atw tower, I reported it. They said they were talking to him and he was sight-seeing around the shore of the lake. Because I was the lower plane in a high wing, and he was higher in a low wing, we never saw each other.

Original NASA ASRS Text

Title: IFR C172 VECTORED TO ILS BY GRB CTLR EXPERIENCED NMAC WITH VFR ACFT.

Narrative: I WAS ON AN IFR FLT PLAN IN VMC FROM 57C TO ATW. I WAS HANDED OFF FROM ZAU TO GRB APCH. SHORTLY AFTER THE HDOF, GRB ASKED ME IF I HAD TFC AT MY 3 O'CLOCK POS, IN REAL CLOSE. I CHKED AND COULDN'T SEE ANYTHING. THEN GRB SAID THE TARGET DISAPPEARED AND THEY SUSPECTED A 'SPLIT BEACON.' I WAS ON A 360 DEG VECTOR UP THE E SIDE OF LAKE WINNEBAGO, BEING VECTORED FOR THE ILS RWY 29 AT ATW. THE INTERCEPT TAKES PLACE ON THE N SIDE OR THE LAKE. GRB TURNED ME IN ON THE INTERCEPT AND CLRED ME FOR THE APCH. I WAS AT 3000 FT. SHORTLY AFTER MAKING THE TURN INBOUND, THEY TOLD ME TO CALL ATW TWR. AT THE SAME TIME, I SPOTTED THE OTHER PLANE DIRECTLY ABOVE ME AND SLIGHTLY AHEAD. WE HAD 300-500 FT OF VERT SEPARATION. I RPTED IT TO GRB APCH, AND THEY SAID IT MUST NOT HAVE BEEN A SPLIT BEACON AFTER ALL. OUR 2 TARGETS WERE MERGED THE ENTIRE TIME. GRB SAID THEY WERE NOT TALKING TO HIM. WHEN I SWITCHED TO ATW TWR, I RPTED IT. THEY SAID THEY WERE TALKING TO HIM AND HE WAS SIGHT-SEEING AROUND THE SHORE OF THE LAKE. BECAUSE I WAS THE LOWER PLANE IN A HIGH WING, AND HE WAS HIGHER IN A LOW WING, WE NEVER SAW EACH OTHER.

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.