Cmh local controller observed a flashing conflict alert on radar but did not hear the audible alert.

Attributes
ACN	635349
Time
Date	200410
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : cmh.airport
State Reference	OH
Altitude	msl single value : 2500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : cmh.tower
Operator	general aviation : corporate
Make Model Name	Cessna 210 Centurion / Turbo Centurion 210C, 210D
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	cruise : level
Flight Plan	None
Aircraft 2
Controlling Facilities	tower : cmh.tower
Operator	general aviation : personal
Make Model Name	Skylane 182/RG Turbo Skylane/RG
Operating Under FAR Part	Part 91
Flight Phase	descent : intermediate altitude
Route In Use	approach : traffic pattern approach : visual
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : local
Qualification	controller : radar pilot : instrument
Experience	controller radar : 22 controller time certified in position1 : 11 flight time total : 1000
ASRS Report	635349
Person 2
Affiliation	government other
Function	flight crew : single pilot
Events
Anomaly	conflict : airborne less severe non adherence : far other anomaly other
Independent Detector	atc equipment : conflict alert other controllera
Resolutory Action	other
Supplementary
Problem Areas	ATC Human Performance ATC Facility
Primary Problem	ATC Facility
Air Traffic Incident	Intra Facility Coordination Failure
Situations
ATC Facility	radar equipment : cmh.tower
Airspace Structure	class c : cmh.c

Narrative:

I was working local. A C182 was set up for sequence to runway 10R, swbound on angling left base. A C210 was conducting surveillance in northwest quadrant of our tower airspace at 2500 ft MSL. Final radar was presumably working both aircraft. I noticed that these 2 aircraft were going to pass closely to each other. Conflict alert began flashing. I then came to realize that there was no audible alert associated with the flashing. It was like this for the rest of the shift. I reported it, but there were other more pressing matters taking place. That was friday. On sunday I worked tower again. It still wasn't working!

Original NASA ASRS Text

Title: CMH LCL CTLR OBSERVED A FLASHING CONFLICT ALERT ON RADAR BUT DID NOT HEAR THE AUDIBLE ALERT.

Narrative: I WAS WORKING LCL. A C182 WAS SET UP FOR SEQUENCE TO RWY 10R, SWBOUND ON ANGLING L BASE. A C210 WAS CONDUCTING SURVEILLANCE IN NW QUADRANT OF OUR TWR AIRSPACE AT 2500 FT MSL. FINAL RADAR WAS PRESUMABLY WORKING BOTH ACFT. I NOTICED THAT THESE 2 ACFT WERE GOING TO PASS CLOSELY TO EACH OTHER. CONFLICT ALERT BEGAN FLASHING. I THEN CAME TO REALIZE THAT THERE WAS NO AUDIBLE ALERT ASSOCIATED WITH THE FLASHING. IT WAS LIKE THIS FOR THE REST OF THE SHIFT. I RPTED IT, BUT THERE WERE OTHER MORE PRESSING MATTERS TAKING PLACE. THAT WAS FRIDAY. ON SUNDAY I WORKED TWR AGAIN. IT STILL WASN'T WORKING!

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.