B-727 less than standard wake turbulence separation from B-757. System error.

Attributes
ACN	286718
Time
Date	199410
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ord
State Reference	IL
Altitude	msl bound lower : 2000 msl bound upper : 2000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B727 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
ASRS Report	286718
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence : published procedure
Independent Detector	other controllera
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Miss Distance	horizontal : 15000
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error
Situations
ATC Facility	procedure or policy : unspecified

Narrative:

The ord TRACON uses ARTS IIIA as a radar tracking device for ATC. The data has call sign, altitude, and timeshares speed and type. We have type timeshare disabled between 30 mi and 5 mi because controllers want to see ground speed at all times. Once an aircraft is inside 5 mi on the approach, the type is displayed. I believe we must see ground speed at all times. However, because the B-757 has no additional identifier indicating the need for wake turbulence separation, we are placing aircraft in an unsafe distance behind B-757's. I was vectoring aircraft to ILS runway 22R. I had built a gap between 2 aircraft straight-in, and posed a B-727 in the gap. Spacing was sufficient to provide for 2 1/2 mi at touchdown. While scanning the final, I observed the B-727 2 1/2 mi behind the preceding aircraft was a B-757. Separation required was 4 mi. Because of the volume of traffic we work and the procedure of discarding the flight progress strip, I did not provide adequate spacing for wake turbulence to the B-727. Aircraft involved were air carrier X (B-757) and air carrier Y (B-727).

Original NASA ASRS Text

Title: B-727 LESS THAN STANDARD WAKE TURB SEPARATION FROM B-757. SYS ERROR.

Narrative: THE ORD TRACON USES ARTS IIIA AS A RADAR TRACKING DEVICE FOR ATC. THE DATA HAS CALL SIGN, ALT, AND TIMESHARES SPD AND TYPE. WE HAVE TYPE TIMESHARE DISABLED BTWN 30 MI AND 5 MI BECAUSE CTLRS WANT TO SEE GND SPD AT ALL TIMES. ONCE AN ACFT IS INSIDE 5 MI ON THE APCH, THE TYPE IS DISPLAYED. I BELIEVE WE MUST SEE GND SPD AT ALL TIMES. HOWEVER, BECAUSE THE B-757 HAS NO ADDITIONAL IDENTIFIER INDICATING THE NEED FOR WAKE TURB SEPARATION, WE ARE PLACING ACFT IN AN UNSAFE DISTANCE BEHIND B-757'S. I WAS VECTORING ACFT TO ILS RWY 22R. I HAD BUILT A GAP BTWN 2 ACFT STRAIGHT-IN, AND POSED A B-727 IN THE GAP. SPACING WAS SUFFICIENT TO PROVIDE FOR 2 1/2 MI AT TOUCHDOWN. WHILE SCANNING THE FINAL, I OBSERVED THE B-727 2 1/2 MI BEHIND THE PRECEDING ACFT WAS A B-757. SEPARATION REQUIRED WAS 4 MI. BECAUSE OF THE VOLUME OF TFC WE WORK AND THE PROC OF DISCARDING THE FLT PROGRESS STRIP, I DID NOT PROVIDE ADEQUATE SPACING FOR WAKE TURB TO THE B-727. ACFT INVOLVED WERE ACR X (B-757) AND ACR Y (B-727).

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.