Ord controller experiences amass alert with no visual conflicting traffic.

Attributes
ACN	575934
Time
Date	200303
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord.airport
State Reference	IL
Altitude	agl single value : 0
Environment
Flight Conditions	IMC
Weather Elements	Snow Fog
Light	Daylight
Aircraft 1
Controlling Facilities	tower : ord.tower tower : mdw.tower
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 9l
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : local
Qualification	controller : radar
Experience	controller limited radar : 10 controller non radar : 2 controller radar : 5
ASRS Report	575934
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	conflict : ground less severe ground encounters : vehicle other anomaly other
Independent Detector	atc equipment other atc equipment : amass other controllera
Resolutory Action	controller : issued new clearance
Supplementary
Problem Areas	Navigational Facility
Primary Problem	Navigational Facility

Narrative:

Aircraft X ILS runway 9L approach to visual conditions. Deicer team (deicer 3) to cross runway 4 and to hold short of runway 9L with acknowledgement. There was an amass alert that the runway was occupied. I scanned the runway, and the deicing team had stopped short of the runway. I then scanned the rest of the runway for other vehicles and aircraft, and the runway was clear. I then decided to allow the aircraft to land.

Original NASA ASRS Text

Title: ORD CTLR EXPERIENCES AMASS ALERT WITH NO VISUAL CONFLICTING TFC.

Narrative: ACFT X ILS RWY 9L APCH TO VISUAL CONDITIONS. DEICER TEAM (DEICER 3) TO CROSS RWY 4 AND TO HOLD SHORT OF RWY 9L WITH ACKNOWLEDGEMENT. THERE WAS AN AMASS ALERT THAT THE RWY WAS OCCUPIED. I SCANNED THE RWY, AND THE DEICING TEAM HAD STOPPED SHORT OF THE RWY. I THEN SCANNED THE REST OF THE RWY FOR OTHER VEHICLES AND ACFT, AND THE RWY WAS CLR. I THEN DECIDED TO ALLOW THE ACFT TO LAND.

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.