T75 approach controller cites 2 call sign events caused by 2 very similar call signs with 4 digits.

Attributes
ACN	579807
Time
Date	200304
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : t75.tracon
State Reference	MO
Environment
Flight Conditions	VMC
Aircraft 1
Controlling Facilities	tracon : t75.tracon tower : cmi.tower
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude descent : approach
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : t75.tracon
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	descent : approach descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller military : 4 controller radar : 25.5 controller time certified in position1 : 11 flight time total : 65
ASRS Report	579807
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	non adherence : clearance non adherence : published procedure other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance controller : separated traffic
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	ATC Human Performance

Narrative:

Air carrier X and air carrier Y call signs confused by pilots. They heard 'air carrier' and end numbers in their callsign. They thought it was for them and responded for the other aircraft. I caught and corrected it. Later that evening, the exact same thing happened with air carrier Z and air carrier west. The 4 digit call signs create confusion in the cockpit and in ATC facilities. With all the required phraseology, there is simply too many numbers flying around the airwaves. Pilots and controllers must really listen up! Controllers are 100% responsible for wrong or missed readbacks. Simply make pilots 50% responsible and controllers 50% responsible and many hearback/readback errors would be eliminated!

Original NASA ASRS Text

Title: T75 APCH CTLR CITES 2 CALL SIGN EVENTS CAUSED BY 2 VERY SIMILAR CALL SIGNS WITH 4 DIGITS.

Narrative: ACR X AND ACR Y CALL SIGNS CONFUSED BY PLTS. THEY HEARD 'ACR' AND END NUMBERS IN THEIR CALLSIGN. THEY THOUGHT IT WAS FOR THEM AND RESPONDED FOR THE OTHER ACFT. I CAUGHT AND CORRECTED IT. LATER THAT EVENING, THE EXACT SAME THING HAPPENED WITH ACR Z AND ACR W. THE 4 DIGIT CALL SIGNS CREATE CONFUSION IN THE COCKPIT AND IN ATC FACILITIES. WITH ALL THE REQUIRED PHRASEOLOGY, THERE IS SIMPLY TOO MANY NUMBERS FLYING AROUND THE AIRWAVES. PLTS AND CTLRS MUST REALLY LISTEN UP! CTLRS ARE 100% RESPONSIBLE FOR WRONG OR MISSED READBACKS. SIMPLY MAKE PLTS 50% RESPONSIBLE AND CTLRS 50% RESPONSIBLE AND MANY HEARBACK/READBACK ERRORS WOULD BE ELIMINATED!

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.