Light transport Y had less than standard separation from air carrier X. System error.

Attributes
ACN	167185
Time
Date	199101
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : bos
State Reference	MA
Altitude	agl bound lower : 300 agl bound upper : 1100
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tower : bos
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent : approach
Route In Use	approach : straight in
Flight Plan	IFR
Aircraft 2
Operator	other
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Flight Phase	descent : approach landing : go around
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : local
Qualification	controller : radar
Experience	controller non radar : 3 controller radar : 1
ASRS Report	167185
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation other anomaly other
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance flight crew : exited adverse environment other
Consequence	Other
Miss Distance	horizontal : 15000
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X was on final (ILS/DME) to runway 33L at bos. Air carrier X slowed to 120 KTS on a 3 mi final. Light transport Y was on approach 3-4 mi in trail 170 KTS. (All speeds are ARTS generated in the data blocks.) light transport Y was told he was indicating 50 KTS faster than air carrier X. Air carrier X was told that traffic was spaced on him. With air carrier X less than a 1 mi final and light transport Y 2 1/2 mi in trail, light transport Y informed me he was unable to follow air carrier X and was aborting the approach. When I asked to say again, the pilot stated he was in a right turn. I asked the pilot if he was able runway 27, and he stated affirmative. The pilot was issued landing clearance for runway 27. During the sequence of events, the pilot of light transport Y never reduced his airspeed and never informed air carrier X (he informed the ground controller of the wake turbulence problem). Bos tower is allowed reduced sep inside the OM (per FAA handbook 7110.65, paragraph 5-72f) to 2.5 mi. Heavy aircraft can participate as trailing aircraft only. Since light transport Y reported air carrier X in sight, I assumed he was providing his own visibility sep (I had both aircraft in sight). Had I known that the wake turbulence from the air carrier created such a problem for the light transport, I would have taken more positive action (i.e., instructed light transport Y to reduce to his final approach speed, if practical) to maintain as much sep as possible.

Original NASA ASRS Text

Title: LTT Y HAD LESS THAN STANDARD SEPARATION FROM ACR X. SYSTEM ERROR.

Narrative: ACR X WAS ON FINAL (ILS/DME) TO RWY 33L AT BOS. ACR X SLOWED TO 120 KTS ON A 3 MI FINAL. LTT Y WAS ON APCH 3-4 MI IN TRAIL 170 KTS. (ALL SPDS ARE ARTS GENERATED IN THE DATA BLOCKS.) LTT Y WAS TOLD HE WAS INDICATING 50 KTS FASTER THAN ACR X. ACR X WAS TOLD THAT TFC WAS SPACED ON HIM. WITH ACR X LESS THAN A 1 MI FINAL AND LTT Y 2 1/2 MI IN TRAIL, LTT Y INFORMED ME HE WAS UNABLE TO FOLLOW ACR X AND WAS ABORTING THE APCH. WHEN I ASKED TO SAY AGAIN, THE PLT STATED HE WAS IN A RIGHT TURN. I ASKED THE PLT IF HE WAS ABLE RWY 27, AND HE STATED AFFIRMATIVE. THE PLT WAS ISSUED LNDG CLRNC FOR RWY 27. DURING THE SEQUENCE OF EVENTS, THE PLT OF LTT Y NEVER REDUCED HIS AIRSPD AND NEVER INFORMED ACR X (HE INFORMED THE GND CTLR OF THE WAKE TURB PROB). BOS TWR IS ALLOWED REDUCED SEP INSIDE THE OM (PER FAA HANDBOOK 7110.65, PARAGRAPH 5-72F) TO 2.5 MI. HVY ACFT CAN PARTICIPATE AS TRAILING ACFT ONLY. SINCE LTT Y RPTED ACR X IN SIGHT, I ASSUMED HE WAS PROVIDING HIS OWN VIS SEP (I HAD BOTH ACFT IN SIGHT). HAD I KNOWN THAT THE WAKE TURB FROM THE ACR CREATED SUCH A PROB FOR THE LTT, I WOULD HAVE TAKEN MORE POSITIVE ACTION (I.E., INSTRUCTED LTT Y TO REDUCE TO HIS FINAL APCH SPD, IF PRACTICAL) TO MAINTAIN AS MUCH SEP AS POSSIBLE.

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.