Air carrier increased rate of descent to avoid confliction with non identified aircraft.

Attributes
ACN	112102
Time
Date	198905
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : buf
State Reference	NY
Altitude	msl bound lower : 3700 msl bound upper : 4000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : buf tower : bdl
Operator	common carrier : air carrier
Make Model Name	Medium Transport, High Wing, 2 Turboprop Eng
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Transport, Low Wing, 2 Recip Eng
Flight Phase	cruise other
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
ASRS Report	112102
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	non adherence : far other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 300
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

The following incident occurred on 5/X/89 while working at buf tower, and while working buf approach control, arrival east position. I was controling air carrier X, who I had on a routine vector 12-13 NM east of buf for the ILS runway 23 approach, and issued descent from 6000 to 4000'. I observed VFR traffic pop-up at air carrier X's 1-2 O'clock position, 1-2 mi at 4000'. I pointed out the traffic to air carrier X because he was below 5000' descending to 4000'. Air carrier X did not see the traffic, so I descended him to 2500'--because in my opinion, the angle and rates of closure between the 2 aircraft negated a turn for air carrier X,and a turn would have put him in an unsafe position. Air carrier X advised he then saw the aircraft and had had to descend to 3700' to miss him. Air carrier X said the VFR aircraft was 'scud-running' at the bases of the clouds. Air carrier X then requested to file a near miss report. I gave him the facility phone # and asked him to call when he landed at buf.

Original NASA ASRS Text

Title: ACR INCREASED RATE OF DESCENT TO AVOID CONFLICTION WITH NON IDENTIFIED ACFT.

Narrative: THE FOLLOWING INCIDENT OCCURRED ON 5/X/89 WHILE WORKING AT BUF TWR, AND WHILE WORKING BUF APCH CTL, ARR E POS. I WAS CTLING ACR X, WHO I HAD ON A ROUTINE VECTOR 12-13 NM E OF BUF FOR THE ILS RWY 23 APCH, AND ISSUED DSCNT FROM 6000 TO 4000'. I OBSERVED VFR TFC POP-UP AT ACR X'S 1-2 O'CLOCK POS, 1-2 MI AT 4000'. I POINTED OUT THE TFC TO ACR X BECAUSE HE WAS BELOW 5000' DSNDING TO 4000'. ACR X DID NOT SEE THE TFC, SO I DSNDED HIM TO 2500'--BECAUSE IN MY OPINION, THE ANGLE AND RATES OF CLOSURE BTWN THE 2 ACFT NEGATED A TURN FOR ACR X,AND A TURN WOULD HAVE PUT HIM IN AN UNSAFE POS. ACR X ADVISED HE THEN SAW THE ACFT AND HAD HAD TO DSND TO 3700' TO MISS HIM. ACR X SAID THE VFR ACFT WAS 'SCUD-RUNNING' AT THE BASES OF THE CLOUDS. ACR X THEN REQUESTED TO FILE A NEAR MISS RPT. I GAVE HIM THE FAC PHONE # AND ASKED HIM TO CALL WHEN HE LANDED AT BUF.

Data retrieved from NASA's ASRS site as of August 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.